EPA 903-R-00-001
                                    CBP/TRS 232/00
                                    April 2000
    Chesapeake Bay
        NTRODUCTION
                                       to an
                      o-
         3- 3 c o
         = ~ ^ 2.
w
n
O
                    ILS.EPAKegicnill
                       pl Center lor Environmental
                    1G50 Arcli Street (o?M32i
                                        CA>
Callinectes sapidus
Fossil
Shark
Tooth
                                      Chesapeake Bay Program
                           Oxyrhina desori
                                    EPA Report Collection
                                    Regional Center for Environmental Information
                                    U.S. EPA Region III
                                    Philadelphia, PA 19103

-------
Regional Center for Fm ironmenlal Information
        US EPA Region III
          1650 Arch St.
       Philadelphia, PA 19103
Note: This edition of Chesapeake Bay: Introduction to an Ecosystem is an update of the 1994 edition
                        and includes information through December 1999.
                                        1994 Version

                                            Editor
                                      Kathryn Reshetiloff

                                   Illustrations and Layout
                                        Sandra Janniche

                                          Reviewers
                                        Richard Batiuk
                                        Peter Bergstrom
                                         Carin Bisland
                                        Walter Boynton
                                         Sherri Cooper
                                        Eugene Cronin
                                        Richard Everett
                                        Douglas Forsell
                                    Eileen Setzler-Hamilton
                                      Michael Hirshfield
                                         Carl Hershner
                                       Frederick Howard
                                         Steven Jordan
                                        Robert Lippson
                                         Lori Mackey
                                      Tamara McCandless
                                        Kent Mountford
                                        Kate Naughten
                                          Robert Orth
                                         Nita Sylvester
                                      Christopher Victoria
                       Chesapeake Bay Program
      ) Recycled/Recyclable—Printed with Vegetable Oil Based Inks on Recycled Paper (30% Postconsumer)

           Printed by the U.S. Environmental Protection Agency for the Chesapeake Bay Program

-------
Contents,
                                                     al Center for Environmental
                                                 Information
                                               1650 kroh Street (3PM52)
                                               Philadelphia, PA 19103
              THE CHESAPEAKE BAY ECOSYSTEM  	  1
                   The Watershed  	  1
                   The Chesapeake Bay—An Important Resource  	  2
                   A Threatened Resource 	  3

              GEOLOGY OF THE CHESAPEAKE	  5
                   Geologic History  	  5
                   The Chesapeake Bay  	  5
                   Erosion and Sedimentation  	  6

              WATER & SEDIMENTS  	  8
                   Water: Salinity, Temperature and Circulation  	  8
                   Suspended Sediments: Composition and Effects 	 10
                   Chemical Make-up 	 10

              HABITATS  	 14
                   Islands and Inlands 	 14
                   Freshwater Tributaries  	 14
                   Shallow Water  	 15
                   Open Water	 15

              LIVING RESOURCES & BIOLOGICAL COMMUNITIES	 16
                   Wetlands 	 17
                   Underwater Bay Grasses 	 18
                   Plankton 	20
                   The Swimmers  	21
                   Life at the Bottom  	22

              FOOD PRODUCTION & CONSUMPTION                             24
                   The Food Web  	25
                   Direct and Detrital Pathways  	26

              PRESERVING THE CHESAPEAKE BAY: THE BIG PICTURE              28
                   Be Part of the Solution, Not Part of the Problem 	29
                   For More Information 	30

-------
The Chesapeake Bay
Watershed
                            L_
                             j Chesapeake Bay Watershed

-------
            The   Chesapeake  Bay  Ecosystem
    The physical processes that drive the Chesapeake Bay
    ecosystem sustain the  many habitats  and organisms
found there. Complex relationships exist among the  living
resources of the Bay watershed. Even the smallest of crea-
tures plays a vital role in the overall health and production of
the Bay. Forests and wetlands around the Bay and the entire
watershed filter sediments and pollutants while supporting
birds, mammals and fish. Small fish and crabs find shelter
and food among lush beds of underwater Bay grasses. Unno-
ticed by the naked eye, phytoplankton and microzooplankton
drift with the currents, becoming food for copepods and
small fish. Clams and oysters pump Bay water through their
gills, filtering out both plankton and sediment. During the
fall and winter, waterfowl by the thousands descend upon the
Bay, feeding in wetlands and shallow waters. Bald  eagles
and osprey, perched high above the water, feed perch, men-
haden and other small fish to their young. The spectrum of
aquatic environments, from freshwater to seawater, creates a
unique ecosystem abundant with life.
   The relentless encroachment of people threatens the eco-
logical balance of the Bay. More than 15 million people live,
work and play in the  watershed. Each individual directly
affects the  Bay by adding waste,  consuming resources and
changing the character of the land, water and air that sur-
round it. However, through the choices we  make everyday,
we can lessen our impact  on the Bay's health. We must nur-
ture what scientist Aldo Leopold  once termed as our "wild
rootage"—a recognition of the fundamental connection and
dependency between society and the environment. As advo-
cates for the Bay and its many living resources, we can
preserve the Chesapeake for years to come.

The Watershed
   The Chesapeake Bay receives about half its water volume
from the Atlantic Ocean. The rest drains into the Bay from an
enormous 64,000 square-mile drainage basin or watershed.
The watershed includes parts  of New York, Pennsylvania,
West Virginia, Delaware, Maryland and Virginia and the entire
District of Columbia. Freshwater from springs, streams, small
creeks and rivers flows downhill, mixing with ocean water to
form the estuarine system. Soil, air,
water, plants and animals, including
humans, form a complex web of
interdependencies that make up the
ecosystem. The people living in the
Chesapeake  watershed  play  an
important role in this ecosystem.
The activities and problems occur-
ring throughout the entire watershed
significantly impact the  functions
and relationships  of the Bay.  We
must choose whether our role will
be destructive or productive.
            BAY FACT
           Everyone in the
           watershed lives
          just a few minutes
           from one or more
            than 100,000
          streams and rivers
           draining into the
           Chesapeake Bay.
                                POPULATION: Chesapeake  Bay Watershed
                  2020
             (projected)
                  2000
             (projected)
                  1980
                                           6      8     10    12
                                              Millions of People
14
16
                              18
                                                                                   Chesapeake Bay Ecosystem   1

-------
Waterman handtonging
for oysters.
The Chesapeake Bay—
An Important Resource
  BAY FACT
   Through the years, residents and visitors alike
have found the Chesapeake Bay imposing, yet hos-
pitable. The Algonquin Indians called it "Chssepi-
ooc," meaning great  shellfish  bay.  Spanish
explorers described the Bay as ". . . the best and
largest port in the world." Captain John Smith, an
English  explorer, extolled, "The country  s not
mountainous  nor yet low but such pleasant plain
hills and fertile valleys . . .  rivers and brooks, all running most
pleasantly into a fair Bay." All were impressed with its size,
navigability and abundance of wildlife and food.
   Today, the Bay is  still one of this country's most valuable
natural treasures. Even after centuries of intensive use, the Bay
remains a highly productive natural resource. It supplies mil-
lions of pounds of seafood, functions as a major hub for ship-
ping and commerce,  provides natural habitat for wildlife and
offers a variety of recreational opportunities for residents and
visitors.
   Oysters and blue crabs are famous Bay delicacies. From the
1950s to the 1970s, the average annual oyster catch was about
25 million pounds per year. Since the early 1980s, however, the
catch has declined dramatically due to overharvesting, disease
and  loss or degradation of habitat. As for Etay blue crab har-
vesting, it averaged 80 million pounds annually from  1993 to
1998, contributing more than  a third of the  nation's catch.
Although this figure  is consistent with past harvests, fishing
pressure, both commercial and recreational, continues to grow.
The states of Maryland  and Virginia have  pledged to jointly
manage the Bay's blue crab harvests through pot limits, gear
 Prior to the late
 1800s, oysters
were $o abundant
 that some oyster
   reefs posed
  navigational
 hazards to Boats,
           restrictions and license restrictions. Harvesting of
           soft-shelled clams and an extensive finfish indus-
           try, primarily based on menhaden and striped bass,
           round out the  Chesapeake's commercial seafood
           production. In  1997, the dockside value of  com-
           mercial shellfish and finfish harvests was close to
           $196 million.
              The hospitable  climate,  lush vegetation and
           natural beauty  of the Chesapeake have made it an
           increasingly popular recreational area. Boating,
           crabbing,  swimming, hunting and camping are
major attractions. Both power and sail  boating have grown
dramatically.  In Maryland  and  Virginia, more than 428,000
pleasure boats and other personal craft were registered in  1998.
   Sportfishing is another major recreational activity in the
Chesapeake region. The National Marine Fisheries  Service
estimates that close to 1.4 million anglers took fishing trips in
Maryland and Virginia in 1998.
   The Chesapeake is also a key commercial waterway, with
two major  North Atlantic  ports located here. The Hampton
Roads Complex, which includes Portsmouth, Norfolk, Hamp-
ton and  Newport News, dominates  the mouth of the Bay.
Hampton Roads ranks second in the nation for metric tons of
exports. At the northern end, the Port of Baltimore is ranked
eleventh in  volume of exports in foreign trade. In all, these two
ports handled more than 70 million metric tons of both imports
and exports in 1997.  Both  Baltimore and Hampton Roads are
near the coal-producing regions of Appalachia, making them
essential to exporting coal.
   Shipbuilding and other related industries also depend on the
Bay. Industries and power companies use large volumes of
water from the Bay for industrial processes and cooling.
 Chesapeake Bay: Introduction to an Ecosystem

-------
   Perhaps the Chesapeake's most valuable function, yet
most difficult to put a price tag on, is its role as habitat
for living resources. The Bay and its surrounding
watershed provide homes for a multitude
of plants and animals.
   Waterfowl and other birds migrating along the
Atlantic Flyway stop here, finding food and shelter
in coves and marshes. The Chesapeake is the winter
home for tundra swans, Canada geese and a variety
of ducks, including canvasbacks, pintails, scoters,
eiders and ruddy ducks. On average, nearly a million
waterfowl winter each year on the Bay. It is also a
major nesting area for the threatened bald eagle.
The nation's largest population of another raptor,
the osprey, is in the  Bay region.
   The Chesapeake's tidal freshwater tributaries
provide spawning and nursery sites for several
important species offish, such as white and yellow
perch, striped bass, herring and shad. During the
warmer months, numerous marine  species,
including bluefish, weakfish,  croaker, menhaden,
flounder and spot, enter the Bay to feed on
its rich food supply.


A Threatened Resource
   The Chesapeake  Bay, the  largest
estuary in the United States,  is part
of an extremely productive and
complex ecosystem. This ecosystem
consists of the Bay,  its tributaries and the
living resources it supports. Humans, too, are a part of this
ecosystem. We  are beginning to understand how our activi-
ties affect the Bay's ecology. Growing commercial, indus-
trial, recreational and urban activities continue to threaten
the Bay and its  living resources.
   Overharvesting and loss of habitat threaten fish and shell-
fish species. These two factors, plus disease, have decimated
the oyster population. Excess sediment and nutrients endan-
ger the Bay's water  quality. Hypoxia (low dissolved oxygen)
and anoxia (absence of dissolved oxygen) are particularly
harmful to bottom-dwelling (benthic) species. Chemical con-
taminants,  particularly high in industrialized  urban areas,
accumulate in the tissues of birds, fish and shellfish. Three
areas, known as Regions of Concern, where living resources
likely are  being affected by  chemical contaminants are  the
Baltimore Harbor/Patapsco River in Maryland, the Anacostia
            Canada goose
          (Branta canadensis)
                                  BAY FACT
The Chesapeake is
 fairly shallow. A
person six feet tall
 could wade over
  700,000 acres
    of the Bay
without Becoming
    completely
                                 Canvasback
                               (Aythya valisineria)
      Osprey
1 (Pandion haliaetus)
                     Great blue heron
                     (Ardea herodias)
             Tundra swan
         (Cygnus columbianus)
                                                                                           Chesapeake Bay Ecosystem

-------
River in the District of Columbia and the Elizabeth
River in Virginia.
   To find the causes of and potential remedies for
these problems, it is necessary to see the Bay from
an ecological perspective. All  too often we think of
ourselves as external to our environment and ignore
the many relationships that link people, other living
creatures and the surrounding habitat. If we ignore
these connections when seeking solutions to prob-
lems, more and greater problems may result
   For example, agricultural activities and res idential develop-
ment increase the amount of sediment and nutrient-rich fertil-
izers entering the Bay through  runoff. Water clarity is reduced
and rivers are silted in. Excess nutrients cause algal blooms that
block sunlight from  reaching critical underwater Bay grasses
known as submerged aquatic vegetation or SAV. As Bay grass
acreage declines, so does the food, shelter and nursery grounds
for many aquatic species.  Solutions to  these environmental
problems can only be effective  if complex relationships among
all components of the ecosystem also are considered.
   When environmental problems  are approached  from an
ecosystem perspective, both living and non-living components
  BAY FACT
  More than a
   third of the
nation's catch of
blue crabs comes
 from the Bay,
             are considered when recommending solutions.
             A truly effective solution not only corrects the
             problem, but avoids damaging other relation-
             ships within the ecosystem. This approach
             makes problem-solving  a great deal more
             challenging, but leads to more effective envi-
             ronmental management.
                The Chesapeake Bay as we know it today
             is the result of thousands of years of continu-
ous change. The Chesapeake, less than  10,000 years old,
continues to change. Nature, like a dissatisfied artist, is con-
stantly reworking the details. Some modifications enhance
the Bay; others harm it. All affect the ecosystem and its inter-
dependent parts. Some changes are abrupt, while others take
place over such a long time that we can only recognize them
by looking back into geologic history.
   Humans  are becoming more  involved in the reshaping
process, often inadvertently initiating chains of events that
reverberate  through the  Bay's   ecosystem.  Because  our
actions can have devastating effects on the entire system, it
is essential that we develop an adequate understanding of the
Bay's geological make-up and fundamental characteristics.
Chesapeake Bay: Introduction to an Ecosystem

-------
                   Geology  of  the  Chesapeake
Geologic History
     During the latter part of the Pleistocene
     epoch, which began  one  million
years ago,  the region  that  is now  the
Chesapeake was alternately exposed and
submerged  as massive glaciers advanced
and retreated up and down the North Amer-
ican continent. Sea levels rose and fell in con-
cert  with glacial contraction and expansion.
The  region  still experiences changes in sea
levels, easily observed over the duration of
a century.
   The most recent retreat of the glaciers,
which began about 18,000 years ago, marked
the end of the Pleistocene epoch and brought
about the birth of the Chesapeake Bay. The rising
waters from melting glaciers covered the conti-
nental shelf and reached the  mouth of the Bay
about 10,000 years ago.  Sea level  continued to
rise,  eventually submerging the area now
known as the Susquehanna River Valley. The
Bay assumed  its present dimensions about
3,000  years  ago.  This complex array of
drowned streambeds forms the Chesapeake basin
we know today.
The Chesapeake Bay
   The Bay proper is approximately 200
 miles long, stretching from Havre de
 Grace, Maryland, to Norfolk, Virginia. It
 varies in width from about 3.4 miles
 near Aberdeen, Maryland, to 35 miles at
 its widest point, near the mouth of the
 Potomac River. Including its tidal tributaries,
 the Bay has approximately 11,684 miles of
 shoreline.
   Fifty major tributaries pour water into the
 Chesapeake every day. Eighty to 90% of the
 freshwater entering the Bay comes from the
 northern and western sides. The remaining
 10 to 20% is contributed by the eastern
 shore. Nearly an equal volume of saltwater
 enters the Bay from the ocean.
            D3
A
Broad Ribbed scallop
(Lyropecten santamaria)
Turret snail (Turritella plebia)
Ark (Anadora stammea)
Shark teeth
1 (Otoc/as obliquus)
2 (/-/em/pr/st/i serra)
3 (Oxyrhina desori)
 On average, the Chesapeake holds more
 than 15 trillion gallons of water. Although
   the Bay's length and width are dramatic,
    the average depth is only about 21  feet.
     The Bay is shaped like a shallow  tray,
     except for a few deep troughs believed
     to be  remnants  of the  ancient  Susque-
   hanna River. The troughs form  a  deep
channel along much of the length of the Bay.
 This channel allows passage of large com-
    mercial vessels. Because it is so shallow,
    the Chesapeake is far more sensitive to
     temperature fluctuations and wind than
     the open ocean
       To  adequately define the Chesapeake
   ecosystem, we must go far beyond the
 shores of  the Bay itself. Although the Bay
 lies totally within the Atlantic Coastal Plain,
 the watershed includes  parts of the Pied-
 mont  Province  and  the  Appalachian
 Province  The tributaries provide a mixture
of waters with a broad geochemical range to
    the Bay. These three different geological
    provinces influence the Bay. Each  con-
    tributes its mixture of minerals, nutrients
    and sediments.
      The  Atlantic  Coastal Plain is a flat,
     low land area with  a maximum eleva-
     tion of about 300 feet above sea level.
     It is  supported by a bed of crystalline
     rock,  covered  with  southeasterly-
    dipping  wedge-shaped  layers  of  rela-
 tively unconsolidated sand, clay and gravel.
   Water passing through this loosely com-
    pacted  mixture  dissolves many  of the
    minerals. The most soluble elements are
    iron, calcium and magnesium.
      The  Atlantic  Coastal Plain  extends
   from the edge of the continental shelf, to
   the east, to a fall line that ranges  from 15
   to 90 miles west of the Bay. This fall line
   forms the boundary between the Piedmont
   Plateau and the Coastal  Plain. Waterfalls
   and rapids clearly mark this line, which is
   close to Interstate 95.  Here, the elevation
                                                                                     Geology of the Chesapeake

-------
                           THE CHESAPEAKE BAY_
                                WATERSHED/'"'
                              '^~->
      I Appalachian Province
      | Piedmont Plateau
  ^;4 Atlantic Coastal Plain
rises to  1,100 feet. Cities such as Fredericksburg and Rich-
mond in Virginia, Baltimore in Maryland, and the District of
                       Columbia developed along the fall
                       line taking advantage of the poten-
                       tial  water power generated by the
                       falls. Since colonial  ships could not
                       sail past the fall line,  cargo would
                       be transferred to canals or overland
                       shipping. Cities along the fall line
                       became   important   areas   for
                       commerce.
                         The  Piedmont  Plateau  ranges
from the fall line m the east to the Appalachian Mountains in
the west. This area is divided into two geologically distinct
 BAY FACT
  More than
600 species are
fossilized in the
 sediments of
 Culvert Cliffs
 in Maryland,
  regions by Parrs Ridge, which traverses Carroll, Howard
  and Montgomery counties in Maryland and adjacent coun-
  ties in Pennsylvania.  Several types of dense crystalline
  rock,  including slates, schists, marble and granite, com-
  pose the eastern side. This results in a very diverse topog-
  raphy. Rocks of the Piedmont tend to be impermeable, and
  water from the eastern side is low in the calcium  and mag-
 nesium salts. This makes the water soft and easy to lather.
    The western side of the Piedmont consists of sandstones,
 shales  and siltstones, underlain by limestone. This lime-
stone bedrock contributes calcium and magnesium  to its
 water, making it hard. Waters from the western side of Parrs
 Ridge flow into the Potomac River, one of the Bay's largest
 tributaries.
    The Appalachian Province lies  in the western and north-
 ern parts of the watershed. Sandstone, siltstone,  shale and
 limestone form the bedrock. These areas, characterized by
 mountains  and  valleys, are  rich  in coal and natural gas
  deposits.  Water from this  province  flows  to  the  Bay
  mainly via the Susquehanna River.
     The waters that flow into the Bay have different chem-
  ical identities,  depending on  the  geology of  the place
  where the waters originate. In turn, the nature of the  Bay
  itself depends on the characteristics and relative volumes
  of these contributing waters.


 Erosion  and Sedimentation
   Since its formation, the Bay's shore has undergone con-
stant modification by erosion, transport and deposition of
sediments.  In this process, areas of strong relief, like penin-
sulas and headlands, are eroded  and smoothed by currents
and tides, and the materials are deposited in other parts of the
Bay. Sediments may be  deposited in channels. Sediments,
carried by the river currents, also are left at the margins of
the  Bay and major  tributaries,   resulting  in  broad,  flat
deposits of mud  and silt. Colonization of  these areas by
hydrophytic (water-loving) vegetation may stabilize the sed-
iments and wetlands can develop.  Recently, however, wet-
lands along shorelines  have  been  retreating inland as sea
level has risen. The speed at which these actions progress
depends on numerous factors, including  weather, currents,
composition  of the affected  land, tides, wind and human
activities.
   Many of the islands that existed in the Bay during colonial
times are now submerged. Poplar  Island, in Talbot County,
Maryland,  illustrates the erosive forces continuing today. In
the early 1600s,  the  island encompassed  several hundred
Chesapeake Bay: Introduction to an Ecosystem

-------
acres. Over the centuries, rising sea level eroded the perimeter
of Poplar Island. Though still populated by the  1940s, only
200 acres remained and the island had been cut in two. Today,
a chain of small islands  is all that remains of  the original
Poplar Island. Efforts are under way to stabilize  the remnant
acres. In addition, the island's original landmass will be rebuilt
by creating marshes that  will protect the island from further
erosion and provide a haven for birds and other wildlife.
       In contrast, sedimentation also has altered the landscape.
    By the mid 1700s, some navigable rivers were filled in by
    sediment as more land was cleared for agriculture.  Joppa-
    town, Maryland, once a seaport, is now more than two miles
    from water. The  forces of erosion  and sedimentation con-
    tinue to reshape the details of the Bay.
                                                                          Mid-19th Century
                                                                              725 acres
                                                                              Late 1940s
                                                                              200 acres
                                                                                  COACHES
                                                                                   ISLAND
         POPLAR ISLAND: ISLAND EROSION
  —^^



POPLAR
ISLAND
                                                                JEFFERSON
                                                                 ISLAND
                                                                           1993 Remnants
                                                                            100-125 acres
                                                                                   COACHES
                                                                                    ISLAND
                                                                                              Geology of the Chesapeake

-------
          Water  &  Sediments
    Water .  . . approximately 70% of Earth's surface is cov-
    ered by it.  It makes up about 80% of our total body
weight. Without it, we cannot live. Perhaps, because its pres-
ence is so pervasive in our lives, we tend to think of water as
uniform rather than a substance with extremely diverse char-
acteristics and properties.
   In the natural environment, water is never pure. It tends to
hold other substances in solution and easily enters into vari-
ous chemical reactions. As the universal solvent, water is an
important environmental medium. Water normally contains
dissolved gases,  such as oxygen, and a variety of organic
(containing carbon) and inorganic materials. The concentra-
tion and distribution  of these substances car vary within a
single body of water. Add differences in temperature and cir-
culation, which can enhance or retard certain chemical reac-
tions,  and the variety of possible water environments  vastly
increases.
  Of all bodies of water, estuanne systems offer the great-
est physical variability in water composition. An estuary,
according to the late oceanographer Donald W. Pritchard, is
a "... semi-enclosed body of water which has free connec-
tion with the open sea and within which seawater is measur-
ably  diluted by freshwater from land drainage." Within an
estuary, freshwater mixes with saltwater, with each  con-
tributing its own chemical and physical  characteristics. This
creates a range of environments that support a wide variety
of plants and animals.

Water: Salinity, Temperature and Circulation
  The distribution and stability of an estuarine ecosystem,
such as  the Chesapeake Bay,  depend  on three important
physical characteristics of the  water: salinity, temperature
and circulation. Each affects and is affected by the others.
        SPRING
       SALINITY
     in parts per
       thousand
                                      AUTUMN
                                      SALINITY
                                      in parts per
                                      thousand
                 Isohalines mark the salt content of surface water. The salinity gradient varies during the year
                 due to freshwater input: fresher during spring rains, saltier during the drier months of autumn.
Chesapeake Bay: Introduction to an Ecosystem

-------
                               ZONE OF MAXIMUM
                                    TURBIDITY
               '•'•""'"'"  '  "  °
   Salinity is a key factor influencing the physical make-up
of the Bay. Salinity is the number of grams of dissolved salts
in 1,000 grams of water. Salinity is usually expressed in parts
per thousand (ppt). Freshwater contains few salts (less than
0.5  ppt) and is less dense than full ocean strength seawater,
which averages 25 to 30 ppt. Salinity increases with depth.
Therefore, freshwater tends to remain at the surface.
   Seawater from the Atlantic Ocean enters the mouth of the
Bay. Salinity is highest at that point and gradually decreases
as one moves north. Salinity levels within  the Chesapeake
vary widely, both seasonally and from year to year, depend-
ing on the volume  of freshwater flowing into the Bay. On a
map, isohalines or  salinity contours mark the salt content of
surface waters. Because the greatest volume  of freshwater
enters the Bay from northern and western tributaries, isoha-
lines tend to show  a southwest to northeast tilt. The rotation
of Earth also drives this salinity gradient. Known as the Cori-
olis Force, it deflects flowing water to the right in the North-
ern Hemisphere  so that saltier water moving up the Bay is
deflected toward the eastern shore.
   Temperature dramatically changes the rate of chemical
and biological reactions within the water. Because the Bay is
so shallow, its capacity to store heat over time is relatively
small. As a result, water temperature fluctuates throughout
the  year, ranging from 34 to 84 degrees Fahrenheit. These
changes in water temperature influence when plants and ani-
mals feed, reproduce, move locally or migrate. The tempera-
ture profile of the Bay is fairly predictable. During spring and
summer, surface  and shallow waters are wanner than deeper
waters with the coldest  water found at the bottom. Often tur-
bulence of the water helps to break down this layering.
 BAY QUOTE
 ".,. the tide is
also governed fry
the wind. South"
 east makes the
highest flood and
  wrtftwest the
   lowest ef>f>"
Rev, Hugh Jones, 1697
                           Just  as   circulation  moves
                        much-needed blood  throughout
                        the human  body, circulation of
                        water transports plankton,  fish
                        eggs,  shellfish larvae,  sediments,
                        dissolved  oxygen, minerals  and
                        nutrients throughout the Bay.  Cir-
                        culation is driven primarily by the
                        movements of freshwater from the
                        north  and  saltwater  from  the
                        south. Circulation causes nutrients
                        and sediments to be mixed  and
resuspended. This mixing creates a zone of maximum tur-
bidity that, due to the amount of available nutrients, is often
used as a nursery area for fish and other organisms.
   Weather can disrupt or reinforce  this two-layered flow.
Wind plays a role in the mixing of the Bay's waters. Wind
also can raise or lower the level of surface  waters and occa-
sionally reverse the direction  of flow. Strong northwest
winds, associated with high pressure areas, push water away
from the Atlantic  Coast, creating exceptionally low tides.
Strong northeast winds, associated with low pressure areas,
produce exceptionally high tides.
   Together, salinity, temperature  and circulation dictate the
physical characteristics of water. The warmer, lighter fresh-
water flows seaward over a layer of saltier  and denser water
flowing upstream. The opposing movement  of these  two
flows forms saltwater fronts or  gradients that move up and
down the Bay in response to the input of freshwater. These
fronts are  characterized by intensive mixing. A layer sepa-
rating water of different densities,  known as a pycnocline, is
                                                                                                   Water & Sediments

-------
       The change in temperature and salinity divides the Bay into saltier bottom
       water and lighter, fresher surface water. A blurry mixing layer, known as the
       pycnocline, divides the two. Strong winds can pile surface water against one
       shore of the Bay. To reestablish equilibrium, the bottom layer flows up into
       shallower water.
           ^
                                                       ;• PYCNOCUNE
                                                          |  SALT CONTENT
                                                          i (parU/lhou&and)
I
                                                             TEMPERATURE
                                                           (degrees Celsius)
      formed. This stratification varies within any season depend-
      ing on rainfall. Stratification is usually highest in the spring
      as the amount of freshwater in the Bay increases due to melt-
      ing  snow  and  frequent rain. Stratification  is maintained
      throughout summer due to the warming of surface waters.
        In autumn, fresher surface waters cool faster than deeper
      waters and sink Vertical mixing of the two water layers
      occurs rapidly, usually overnight. This mixing moves  nutri-
      ents up from  the bottom, making them available to phyto-
      plankton and other organisms  inhabiting upper water levels.
      This turnover also distributes much-needed dissolved oxygen
      to deeper waters. During the winter, water temperature and
      salinity are relatively constant from surface to bottom.

      Suspended  Sediments:
      Composition and Effects
        The waters of the Chesapeake and its tributaries transport
      huge quantities  of sediments. Although sediments are  a nat-
      ural part of the Bay ecosystem, accumulation  of excessive
      amounts  of sediments  is  undesirable. Accumulation  of
                                                                         sediments can fill in ports and waterways.
                                                                         This  sedimentation process  already  has
                                                                         caused  several  colonial seaports, like Port
                                                                         Tobacco, Maryland, to become landlocked.
                                                                         As they settle to the bottom of the Bay, sed-
                                                                         iments can smother bottom-dwelling plants
                                                                         and  animals, such as oysters  and clams.
                                                                         Sediments suspended in the water column
                                                                         cause the water to become cloudy, or turbid,
                                                                         decreasing the light available for underwa-
                                                                         ter Bay grasses.
                                                                            Sediments also can carry high concen-
                                                                         trations of certain toxic materials. Individ-
                                                                         ual sediment particles have a large surface
                                                                         area, and  many  molecules easily adsorb or
                                                                         attach to them.  As a  result, sediments can
                                                                         act as chemical  sinks by adsorbing metals,
                                                                         nutrients,  oil, pesticides and  other poten-
                                                                         tially toxic  materials.  Thus, areas of high
                                                                         sediment  deposition sometimes have high
                                                                         concentrations  of nutrients,  persistent
                                                                         (long-lasting) chemicals and contaminants,
                                                                         which may later be released.
                                                                            In the  upper Bay  and tributaries,  sedi-
                                                                         ments are fine-grained silts and  clays that
                                                                         are light and can be carried long distances.
                                                                         These sediments are  carried by  the fresh,
                                                                         upper layer of water. As they move into the
                                                                         Bay, the particles slowly descend into the
                                                          denser saline layer. Here, the particles  may reverse direction
                                                          and flow back up toward tidal tributaries with the lower layer
                                                          of water. As the upstream flow decreases, the sediments set-
                                                          tle to the bottom.
                                                             Sediments in the middle Bay are mostly made of silts and
                                                          clays. These sediments mainly  are derived from shoreline
                                                          erosion.  In  the lower Bay,  by  contrast,  the sediments are
                                                          sandier and heavier. These particles result from shore erosion
                                                          and  inputs from the ocean. Sediments drop to the bottom
                                                          fairly rapidly, remain near their original source and are less
                                                          likely to be resuspended than finer silts.

                                                          Chemical Make-up

                                                             Like temperature  and salinity, the chemical composition
                                                          of the water also helps determine the distribution and abun-
                                                          dance of plant and animal  life within the Bay. The waters of
                                                          the  Chesapeake contain organic  and inorganic  materials,
                                                          including dissolved  gases, nutrients,  inorganic  salts, trace
                                                          elements, heavy metals and potentially toxic chemicals.
10
Chesapeake Bay: Introduction to an Ecosystem

-------
   DISSOLVED INORGANIC
      COMPOUNDS tN
         SEAWATSR
       im parts ppr million)
          TfSACf HIMfNIS
              ,95 ppm
                                    Q PURE WATER
                                    H CHEMICAL MAKE-UP
                                M1NOK COMPONENTS
                                    1 MA ppm
380 ppm  WO ppm
  *       I
                    MAJOR COMPONCNTS
                           1350 ppm
                     *       4
   The more saline waters are chemically similar to seawater.
Major  constituents include chlorides,  sodium, magnesium,
calcium and potassium. Dissolved salts are important to the
life cycles of many organisms. Some fish spawn in fresh or
slightly brackish water and must move to more saline waters
as they mature.  These species have internal mechanisms that
enable them to cope with the changes in salinity.
   Seawater also contains hundreds of trace elements that are
important in many biological reactions. For example, living
organisms require minute quantities of cobalt to make  vita-
min B-12. Metals  such as mercury, lead, chromium and cad-
mium also occur in low concentrations.
   The composition of seawater is relatively constant from
place to place. Freshwater, however, varies depending upon
the soil and rocks  with which the water has come in contact.
Both fresh and saltwater contain  a myriad of natural dis-
solved  materials. These  come   from  several  sources.
Microorganisms, such as bacteria,  decompose dead organ-
isms and release compounds into the water. Live organisms
also release compounds directly into the water. In addition,
dissolved material enters the Bay via its tributaries and the
ocean.
                                                                                                  BAY FACT
 Due to a lack of
  oxygen in the
 water, hundreds
  of blue crabs
meat run out onto
 land. TMs rare
  phenomena 1$
   known as A
  *cra6 fuAttee."
        Dissolved oxygen is essential for most animals
     inhabiting the Bay. The  amount of available oxygen is
     affected by salinity and temperature. Cold water can
     hold more dissolved oxygen than warmer water, and
     freshwater holds more  than saline water. Thus, con-
     centrations of dissolved  oxygen vary,  in part, with both
     location and time. Oxygen  is transferred  from the
     atmosphere   into   surface
     waters  by  diffusion and the
     aerating action of the wind. It
     also is  added as  a byproduct
     of  photosynthesis. Floating
     and rooted aquatic plants and
     phytoplankton  release  oxy-
     gen when photosynthesizing.
     Since photosynthesis requires
     light, production of oxygen
     by aquatic plants is limited to
     shallow water areas, usually
     less than six feet deep. Sur-
     face water is nearly saturated with oxygen most of the
     year, while deep bottom waters range  from saturated to
     anoxic (no oxygen present).
        During the winter, respiration  levels of organisms
     are relatively low. Vertical mixing is good, and there is
     little salinity or temperature stratification. As a result,
     dissolved oxygen is plentiful throughout the water col-
     umn.  During the spring and summer, increased levels
of animal and microbial respiration and greater stratification
may reduce vertical mixing, resulting in low levels of dis-
solved oxygen in deep water. In fact, deep parts  of some trib-
utaries like the Patuxent, Potomac and Rappahannock rivers
and deep waters of the Bay's mamstem can become anoxic
in summer. In the autumn when surface  waters cool, vertical
mixing occurs and deep waters are re-oxygenated.
  Carbon dioxide, another dissolved gas, is important to the
well-being of the Bay's aquatic environment. It provides the
carbon that plants  use  to produce new  tissue during photo-
synthesis and is a byproduct of respiration. Carbon dioxide
is more soluble in water than  oxygen. Its availability also is
affected by temperature and salinity in much the same fash-
ion as oxygen.
  Nitrogen is essential to the production of plant and animal
tissue. It is used primarily by plants and animals  to synthesize
protein. Nitrogen enters the ecosystem  in  several  chemical
forms and also occurs in other dissolved or particulate forms,
such as in the tissues of living and dead  organisms.
  Some  bacteria and  blue-green algae  can extract  nitrogen
gas from the atmosphere and transform  it into organic nitro-
                                                                                                  Water & Sediments

-------
                        Sunlight
                                         Minimal
                                       Phosphorus &
                                       Nitrogen Inputs
          Excessive
        Phosphorus &
        Nitrogen Inputs
                         Sunlight
     •  •   Healthy
      ' • Oyster Reef v-'
   ;:;     -,Bent"                                                                   ^ofBenthlccommunrty  :'
                                                                                                          • ff
gen  compounds. This  process,  called  nitrogen  fixation,
cycles nitrogen between organic and inorganic; components.
Other bacteria release nitrogen gas back into the atmosphere
as part of their normal metabolism in a process called deni-
trification. Denitrification removes about 25% of the nitro-
gen entering the Bay each year.
   Phosphorus is another key nutrient in the Bay's ecosys-
tem. In the water, phosphorus  occurs in dissolved organic
and inorganic forms, often attached to particles of sediment.
This nutrient is essential to cellular growth and reproduction.
Phytoplankton and bacteria assimilate and use phosphorus in
their growth cycles. Phosphates (the organic "orm) are pre-
ferred, but organisms will use other forms of phosphorus
when phosphates are unavailable.
   In the presence of oxygen, high  concentrations of phos-
phates in the water will combine with suspended particles.
These particles eventually settle to the Bay bottom and are
temporarily removed  from the  cycling procesis. Phosphates
often become long-term constituents of the bottom sedi-
ments. Phosphorus compounds in the Bay generally occur in
greater concentrations in less saline  areas, such as the upper
part of the Bay and tributaries. Overall, phosphorus concen-
trations vary more in the summer than winter.
   Nutrients,  like nitrogen and phosphorus, occur naturally
in water, soil  and air. Just as the nitrogen and phosphorus in
fertilizer aids the growth of agricultural crops, both nutrients
are vital to the growth of plants within the Bay. Excess nutri-
ents,  however, are  pollutants.  Sewage treatment  plants,
industries, vehicle exhaust, acid  rain, and runoff from agri-
cultural, residential and urban areas are additional sources of
nutrients entering the Bay. Nutrient pollution is the number
one problem in the Bay system.
   Excess amounts of nitrogen and phosphorus cause rapid
growth  of phytoplankton, creating dense populations  or
blooms. These blooms become so dense that they reduce the
amount of sunlight  available to underwater Bay grasses.
Without  sufficient light, plants cannot photosynthesize and
produce the food they need to  survive. Algae also may grow
directly  on the  surface of  Bay  grasses,  blocking  light.
Another hazard of nutrient-enriched algal  blooms  comes
after the algae die. As the blooms decay, oxygen is used up
in decomposition. This can lead to dangerously low oxygen
levels that can harm and even kill aquatic organisms.
Chesapeake Bay: Introduction to an Ecosystem

-------
   Besides nutrients,  people  add other substances  to  the
Bay's water, creating  serious pollution problems.  Heavy
metals,  insecticides, herbicides and a variety  of synthetic
products and byproducts can be toxic to living  resources.
These contaminants reach the Bay through municipal and
industrial wastewater, runoff from agricultural, residential
and urban areas and atmospheric deposition.
   This  situation is improving. In some cases,  industrial
wastewater can be treated to remove contaminants. The use
of especially damaging synthetic substances, like DDT and
Kepone, has been banned.
   In an effort to control nutrient pollution, Maryland, Penn-
sylvania, Virginia and the District of Columbia  agreed  to
reduce the total amount of controllable nutrients entering the
Bay by  40% by 2000. Controllable sources include runoff
from agricultural, suburban and  urban areas, wastewater
treatment plants and industry. A ban  on laundry  detergents
containing phosphates has reduced phosphorus levels. New
technologies at many sewage treatment plants remove some
phosphorus and  nitrogen before the effluent is discharged
into  rivers. Other  efforts  include maintaining forested  or
other vegetated buffer strips along water sources, reducing
fertilizer use on farms and lawns  and managing animal
waste.
                    BAY FACT
                     During the
                   1600s, wolves,
                  cougars, elk and
                    Buffalo still
                   inhabited the
                  Ray watershed.
                                                                                                  Water & Sediments
                                                           13

-------
                      Habitats
         The Bay provides food, water, cover and nesting or nurs-
         ery areas, collectively known as habitat, to more than
      3,000 migratory and resident wildlife species All plants and
      animals have specific habitat requirements that must be sat-
      isfied in order to live  and thrive. Food, temperature, water,
      salinity, nutrients, substrate, light, oxygen and  shelter
      requirements vary with each species. These physical and
      chemical variables largely determine which species can be
      supported by a particular habitat.
        As a highly productive estuary, the Chesapeake Bay pro-
      vides an array  of habitats. Habitat types range from  hard-
      wood forests of the Appalachian mountains to saltwater
      marshes in the Bay. These habitats are influenced by climate,
      soils, water, plant and animal interactions and human activi-
      ties. Four major habitat areas are critical to the survival of the
      living resources of the Bay.

      Islands and  Inlands
        Lands near water sources support a multitude of species,
      from insects, amphibians and reptiles to birds and mammals.
      Streambanks, floodplains  and wetlands  form the
      transition from  water to land. These areas  act as
      buffers by removing sediments, nutrients, organic
      matter and pollutants from runoff before these sub-
      stances can enter the water. Forests and foiested
      wetlands are particularly important to wateifowl,
      other migratory birds and colonial waterbirds.
        Forested uplands and wetlands are nesting and
      resting habitat  for neotropical  migratory  Dirds.
      These birds breed in the United States but winter in
      Central  and South America.  Some neotropical
      birds breed in the forests found in the Bay  water-
      shed. The  Bay lies within the Atlantic Flyway, a
      major migration route for neotropical migrants and
      migrating waterfowl,  and is  a  significant  resting
      area for birds.
        Surrounded by water and cut off from most
      large predators, Bay islands are a haven for colo-
      nial  waterbirds (terns and  herons),  waterfowl
      (ducks)  and raptors  (osprey and bald eagles).
      Islands also can protect underwater Bay grasses
      and shallow water areas  from erosion  and sedi-
      mentation. However, islands themselves are erod-
      ing at alarming rates, mostly due to sea level rise
      and the erosive force of wind and waves.
Freshwater Tributaries
   Within the  Chesapeake  Bay watershed,  five major
rivers—the Susquehanna,  Potomac,  Rappahannock, York
and James—provide  almost 90% of the freshwater to the
Bay. These rivers and other smaller rivers, along with the
hundreds of thousands of creeks and streams that feed them,
provide habitat necessary for the production of many  fish
species. Anadromous  fish spend their adult lives in the ocean
but must spawn in freshwater. Anadromous fish species in
the Bay include striped bass  (rockfish), blueback herring,
alewife, American and hickory shad, shortnose sturgeon and
Atlantic sturgeon. Semi-anadromous fish, such as white and
yellow perch, inhabit tidal tributaries but also require fresh-
water to spawn.
   While all of these species have different habitat require-
ments, all must have access to freshwater spawning grounds.
However, due 1o dams and other  obstacles, many historical
spawning  grounds are no longer  available to fish. Fish not
only need access to spawning grounds but require good
stream and water quality conditions for the development and
14
      Chesapeake Bay: Introduction to an Ecosystem

-------
survival of eggs and juvenile fish. Nutrients,
chemical contaminants, excessive sediment
and low dissolved oxygen degrade spawn-
ing and nursery habitat.

Shallow Water
 BAY QUOTE
                      Open Water
  "In sommer no
  place affordetfi
  more plentie of
 sturgeon, nor in
winter more abun-
dance of foule. .."
 John Smith, 1607-08
   Shallow water provides habitats for many
life stages of invertebrates, fish and water-
fowl  Shrimp,  killifish  and juveniles  of
larger fish species use Bay grass beds, tidal
marshes and shallow shoreline margins as nursery areas and
for refuge. Vulnerable, shedding blue crabs find protection in
grass beds. Predators, including blue crabs, spot, striped bass,
waterfowl,  colonial  waterbirds and raptors, forage for food
there. Along shorelines, fallen trees and limbs also give cover
to small aquatic animals. Even unvegetated areas, exposed at
low  tide, are productive  feeding areas. Microscopic plants
cycle nutrients and are fed upon by crabs and fish.
         Striped bass, bluefish, weakfish, American shad,
       blueback herring, alewife, bay anchovy and Atlantic
       menhaden live in the open,  or pelagic, waters of the
       Bay. Although unseen by the naked eye, microscopic
       plants and animal life  (plankton) float in the open
       waters. These tiny organisms form the food base for
       many other animals. Hundreds of thousands of win-
       tering ducks, particularly sea ducks like scoters,  old-
       squaw and mergansers,  depend on open water for the
shellfish, invertebrates  and fish they eat during  the winter
months. Open water also supports oysters and other bottom-
dwellers. Oysters and other filter feeders help maintain water
quality by  filtering suspended organic  particles  out of the
water. The oyster reef itself is a solid structure that supports
other shellfish, finfish and crabs
                                                                                                           Habitats
                                                                                                                      15

-------
                      Living Resources  &
                      Biological  Communities
          Within every habitat, communities of organisms
          exist in close relationship to each other. Commu-
     nities may be as small as an oyster bar or as large as the
     entire Bay. The relationships among species form a com-
     plex web.  Some organisms produce  food ard others
     serve as prey. Some communities, such as underwater
     Bay grasses, provide both  food and cover.  Many
     organisms fit into more than one of these categories.
     The functions within a given community are almost
     endless, and the Chesapeake Bay supports countless
     communities both large and small.
        Change is characteristic
     of  ecological  systems,
     including the Bay.  Germi-
     nation of plant seeds, birth
     of animals,  growth,  local
     movement and migration
     affect the species composi-
     tion of each community, as
     do changes in water quality, loss of habitat
     or overharvesting.
        Some  variations,   such  as  seasonal
     changes,  follow a predictable pattern.
     Every year, waterfowl migrate to the Bay
     to spend the winter feeding in uplands, wet-
     lands and shallow water areas. Then,  each spring,
     they return to northern parts of the continent
     to breed. After mating each summer, female
     blue crabs migrate to the mouth of the  Bay to
     spawn, while the males remain in the
     upper and middle Bay. Anadro-
     mous fish, like shad and her-
     ring, spend most of their lives
     in the ocean, but each spring
     enter the Bay and migrate into
     freshwater to spawn.  These  are
     just a few of the seasonal vari-
     ations that occur.
        Some  Bay  communities
     are prone  to rapid  population
     fluctuations  of one or more
     species. This is particularly  true  of
     plankton. Rapid changes in  plankton diversity
                                                      Sea Nettle
                                                 (Chrysaora quinquecirrha)
                                        Striped bass
                                      (Morone saxatilis)
                                        American oyster
                                         (Crassosfrea
                                          virgmica)
                                                Blue crab
                                            (Callmectes sapidus)
   and abundance may occur hourly or
   daily due to the interaction of biolog-
       ical, physical  and  chemical
         factors.
            Many   species  exhibit
         long-term patterns in popula-
         tion abundance  and distribu-
        tion. For  example,  croakers
         suffer high mortalities during
         exceptionally cold  weather.
          This fish was  abundant in
           the  Bay during  the  late
           1930s and early 1940s. It is
           believed that relatively mild
          winters in the late 1930s and
            early 1940s promoted the
              high numbers of croak-
               ers.  Human-induced
               pressures  can  affect
               long-term  patterns.
           Striped bass  declined  rap-
            idly in the late  1970s and
            through the  1980s due to
            overharvesting and subse-
            quent reproductive failure.
            However, successful man-
           agement measures led  to a
         restored stock in 1995.
            Individual  species  may
         belong to a variety of commu-
       nities and use different habitats
        throughout their life cycles.
         Habitats  are  connected  and
          communities often overlap.
         Changes in a particular habi-
        tat  not only may affect the
      communities it supports but other
       habitats and communities as
       well.
          In the Chesapeake, wetlands,
      grass beds, plankton, fish and bot-
   tom-dwellers  are biological commu-
nities  supported by the  Bay's diverse
16
Chesapeake Bay: Introduction to an Ecosystem

-------
habitats. Wetlands are transitional areas between water and
land. Bay grass beds range from mean low tide to a depth of
about six  feet  or where light  becomes  limiting to plant
growth, although some freshwater species thrive in water up
to nine feet deep. Open water supports the plankton commu-
nity, composed mostly of minute creatures that float and drift
with the movement of the water, and the nekton community,
the  fish and other  swimmers that move freely throughout the
Bay and its tributaries. The bottom sediments support ben-
thic organisms.

Wetlands
   Wetlands are environments subjected to periodic flooding
or prolonged saturation,  producing specific plant communi-
ties and soil types. The presence of water affects
the  type of soil that develops and the types of
plants and animals  that  live there. Wetlands are
characterized by  hydrophytic vegetation  (water-
loving plants adapted to wet soils)  and hydric
soils  (saturated or periodically  flooded soils).
There are two broad categories of wetlands in the
Bay watershed. Wetlands within the reach  of tides
are  considered  tidal.  Salinity in  tidal  wetlands
ranges from fresh to saltwater. Nontidal or palus-
tnne wetlands are freshwater areas unaffected by
the  tides. Wetlands receive water by rain, ground-
                    BAY FACT
                             are
                    among &e
                  most productive
                 ecosystems in the
                 world, producing
                 more food (In the
                 form of detritus)
                    than many
                 agricultural fields.
water seepage, adjacent streams and, in the case of tidal wet-
lands, tides. Salinity, substrate and frequency of flooding
determine the  specific plant and animal life a wetland can
support.
   Tidal  wetlands  are dominated by nonwoody or herba-
ceous vegetation and are subjected to tidal  flooding. These
wetlands have a low marsh zone (flooded by every high tide)
and a high marsh  zone  (flooded by extremely high tides).
Plants such as  smooth cordgrass are found in the  low marsh
zone  of  brackish and saltwater  marshes. The high marsh
zone  may be  dominated by saltmeadow cordgrass,  black
needlerush,  saltgrass or marsh elder. Freshwater marshes
also have low and  high zones. Along the water's edge, you
may find wild rice, arrow arum, pickerel weed and pond lily.
In the high zone, cattail and big cordgrass may be prevalent.
               Nontidal wetlands frequently contain bul-
            rush,  broad-leaved  cattail, jewel weed,  spike
            rushes and sedges.  Forested  wetlands,  often
            referred to as swamps, may have  permanent
            standing water or may be seasonally flooded.
            Trees commonly found in forested wetlands
            include red maple,  black  gum, river birch,
            black willow,  Atlantic white  cedar and  bald
            cypress. Willows, alders and button  bushes are
            types  of shrubs present in forested wetlands.
               Approximately 1.5  million acres of  wet-
            lands  remain in the  Bay watershed, less than
 A  Button bush
    (Cephalanthus occidentalis)
 B  Big cordgrass
    (Spartina cynosuroides)
C  Narrow-leaved cattail
   (Typha angustifolia)
D  Black needlerush
   (luncus roemerianus)
E  Saltmeadow cordgrass
   (Spartina patens)
  F Wild rice
    (Zizania aquatica)
  C Widgeon grass
    (Ruppia maritima)
                                                                              Living Resources & Biological Communities

-------
                                                                                                  A Black willow
                                                                                                    (Salix nigra)
                                                                                                  B Red maple
                                                                                                    (Acer rubrum)
                                                                                                  C River birch
                                                                                                    (Betula nigra)
                                                                                                  D Jewelweed
                                                                                                    (Impatiens capensis)
                                                                                                  E River bulrush
                                                                                                    (Sdrpus fluviatilis)
                                                                                                  F Broad-leaved cattail
                                                                                                    (Typha latifolia)
      half of the wetlands that were here during colonial times. Of
      the remaining wetlands, 13% are tidal and 87% are nontidal.
        Often  viewed as  wastelands, wetlands were  drained or
      filled for farms, residential developments, commercial build-
      ings, highways and roads. Over the past several decades, our
      understanding and appreciation of wetlands has increased.
        Plant diversity, biochemical reactions and hydrology of
      these  habitats make them  extremely productive. Wetlands
      support large quantities of plant biomass. The  huge amount
      of visible plant  material in wetlands makes  up only the
      above-ground biomass. The below-ground  biomass,  com-
      posed of root and rhizome material, is often  more than dou-
      ble the above-ground  biomass. This creates a tremendous
      reservoir  of nutrients and chemicals bound up in plant tissue
      and sediments.
        Many  of the Bay's living resources depend on these wet-
      land habitats for their  survival. Tidal wetlands are the win-
      tering homes for great flocks of migratory \vaterfowl.  Other
      wildlife,  including muskrats, beavers, otters, songbirds and
      wading birds, rely on wetlands for food and cover. Fish and
      shellfish,  many of which  are  commercially valuable, use
      wetlands  as spawning or nursery areas. Thousands of aquatic
                             animals,    including    reptiles,
                             amphibians, worms, insects, snails,
                             mussels  and  tiny  crustaceans,
                             thrive in wetlands and are food for
                             other organisms.
                                The abundance  of  food and
                             shelter provided by wetland vege-
                             tation is essential to other members
                             of this community.  A  host of inver-
                             tebrates  feed  on  decomposing
                             plants and  animals. This nutrient-
   BAY FACT
  Two-thirds of
   the nation's
 commercial fish
   and shellfish
    depend on
   wetlands as
    nursery or
spawning grounds.
rich detritus is also available to juvenile stages of fish and
crabs. A dense layer of microscopic plants  and animals,
including  bacteria and algae,  coats  the  land surface and
serves as food. Stems of larger plants provide another good
source of food. Decomposing plants and animals are  the
major food source for other wetland inhabitants.
   Wetlands are also important  for  controlling flood and
storm waters. Fast-moving water is slowed by vegetation and
temporarily stored in wetlands. The gradual release of water
reduces erosion and possible property damage. Coastal wet-
lands absorb  the erosive energy of waves, further reducing
erosion.
   Poised between land and water, wetlands act as buffers,
regulating the flow of sediments and nutrients into rivers and
the Bay. As water runs off the land and passes through wet-
lands, it is filtered.  Suspended solids, including sediment
pollutants, settle and are trapped by vegetation. Nutrients,
carried  to wetlands  by tides,  precipitation,  runoff and
groundwater, are trapped and used by wetland vegetation. As
plant material decomposes, nutrients  are released back into
the Bay and its tributaries, facilitated by floodwaters or tides.
   Economically,  wetlands provide opportunities for fishing,
crabbing and hunting. Other popular activities include hik-
ing,  birdwatching, photography and  wildlife  study. People
are lured by the beauty of wetlands to enjoy the sights  and
sounds that these  areas can  offer.

Underwater Bay Grasses
   In the shallow waters of the Bay, underwater grasses sway
in the aquatic breeze of the current.  Known  as submerged
aquatic  vegetation or SAV, these amazing plant communities
provide food and shelter for waterfowl, fish,  shellfish  and
18
      Chesapeake Bay: Introduction to an Ecosystem

-------
invertebrates. Like other green plants,  Bay grasses produce
oxygen, a precious and sometimes lacking commodity in the
Bay. These underwater plants also trap sediment that can
cloud the water and bury bottom-dwelling organisms like
oysters. As waves roll into grass  beds,  the movement is
slowed and energy is dispelled, protecting shorelines from
erosion. During the growing season, Bay grasses take up and
retain nitrogen  and phosphorus, removing excess nutrients
that could fuel unwanted growth of algae in the surrounding
waters.
   Like a forest, field or wetland, a grass bed serves as habi-
tat for many aquatic animals. Microscopic zooplankton feed
on decaying Bay grasses and, in turn, are food for larger Bay
organisms. Minnows dart between  the plants and graze on
tiny organisms that grow on the stems and leaves.  Small fish
seek refuge from larger and hungrier mouths. Shedding blue
crabs conceal themselves in the  vegetation until  their new
shells have hardened. Thus, grasses are a key contributor to
the energy cycling in the Bay. Bay grasses are a valuable
source of food, especially for waterfowl. In the fall and win-
ter, migrating waterfowl search the sediment for nutritious
seeds, roots and tubers. Resident waterfowl may feed on
grasses year-round.
                           There are 14 common species of grasses commonly found
                        in the Bay or nearby rivers. Salinity, water depth and bottom
                        sediment determine where each species can grow. Survival
                        of Bay grasses is affected most by the  amount of light that
                        reaches the plants. Poor water quality resulting in less light
                        penetration is the primary cause for declining grasses.
                           Factors that affect water clarity, therefore, also affect the
                        growth of Bay grasses. Suspended sediment and other solids
                        cloud the water, blocking precious sunlight from the grasses.
                        Excessive amounts of suspended sediment may cover the
                        plants completely. Sources of suspended sediments include
                        runoff from farmland, building sites and highway construc-
                        tion. Shoreline erosion also adds sediment to the Bay. Land
                        development,  boat traffic  and loss of  shoreline  vegetation
                        can accelerate natural erosion.
                           Nutrients,  although vital  to all ecosystems, can create
                        problems when present in excessive amounts. Major sources
                        of nutrients include sewage treatment plants, acid rain, agri-
                        cultural fields  and fertilized lawns. High levels of nutrients
                        stimulate rapid growth of algae,  known  as blooms. Algal
                        blooms cloud  the water and reduce the amount of sunlight
                        reaching Bay grasses. Certain types of algae grow directly on
                        the plants, further reducing available sunlight.
                                 Common  Underwater Bay Grasses
           Widgeon grass
          (Ruppia maritima)
   Eelgrass
(Zostera marina)
    Wild celery
(Vallisneria americana)
     Redhead grass
(Potamogeton perfoliatus)
                                                                              Living Resources & Biological Communities
                                                                                   19

-------
                               Historically, more than 200,000
                            acres of grasses grew along the
                            shoreline of the Bay.  By 1984, a
                            survey of Bay grasses documented
                            only 37,000 acres in the Bay and its
                            tidal  tributaries.  Declining water
                            quality, disturbance of grass beds
                            and  alteration of  shallow water
                            habitat all  contributed  to the Bay-
                            wide  decline.  The  absence  of
                            grasses translates into a loss of food
                            and  habitat for  many  Chesapeake
                            Bay species. However,  Bay grasses
                            have  rebounded steadily since the
                            low point in 1984. In 1998, 63,495
                            acres of grasses were documented.
                               Water quality is the key to restor-
                            ing grasses. Scientists  have identi-
                            fied the  water  quality conditions
                            and requirements necessary for the
                            survival of five grass species: wild
                            celery found  in freshwater,  sago
                            pondweed, redhead grass and wid-
                            geon grass found in nore estuarine
                            water  and  eelgrass  found in the
                            lower  Bay  in  saltier water.  Each
                            species is  an  important  source of
                            food for waterfowl. EJay grasses are
                            making  a  comeback,  however.
                            Water quality  is  beginning to
                            improve  due to the ban of phos-
                            phates in detergents,  reduction of
                            fertilizer use by farrrers and home-
                            owners, protection of shallow water
                            habitat and the reduction of nutri-
                            ents in sewage effluent.

                            Plankton

                               Mainly unseen by the naked eye,
                            a community made up  of predomi-
                            nantly microscopic organisms also
                            fuels the Bay ecosystem. These tiny
                            plants and animals, called plankton,
                            drift  at the mercy  of  the currents
                            and tides.  Some of the  tiny crea-
                            tures move up and down  in the
                            water column  to take advantage of
                            light. Others will drop below the
   BAY FACT
 Owe drop of Bay
water may contain
   thousands of
  phytoplankton.
pycnochne,  an intermediate  layer where the increase  in
salinity is more pronounced,  to avoid being washed out to
the ocean.
   Phytoplankton are tiny single-celled plants. Like higher
plants, phytoplankton require light to live and reproduce.
Therefore, the largest concentrations occur near the surface.
Salinity affects phytoplankton dis-
tribution with the largest number of
species preferring the saltier waters
near the mouth of the  Bay. The
amount of nutrients in the water is a
major determinant to the abundance
of these plants. The largest concen-
trations of  phytoplankton in the
Bay occur during the spring  when
nutrients are  replenished by freshwater  runoff from the
watershed. These high concentrations produce the character-
istic brown-green color of estuarine and near-shore waters.
Although there are many species of phytoplankton, the major
types in the Bay  are  diatoms and  dinoflagellates. When
dinoflagellates dominate  the water,  a red-tinted bloom,
called a mahogany tide, may  be produced. Mahogany  tides
typically occur on warm, calm days, often following  ram.
Diatoms, which are present throughout much of the  year,
may account for 50% of total  algal production.
   Changes  in chemical conditions, such as the addition of
nutrients, can  cause rapid increases in the amount of algae.
These  algal blooms can have serious consequences. They
block light  from reaching SAV beds. Even after they die,
they can cause problems. Deposition and subsequent decom-
position of large masses of plankton in the mainstem of the
Bay can deplete dissolved oxygen, suffocating other estuar-
ine animals.
   Phytoplankton are the major food source for microscopic
animals called zooplankton. Dominating the zooplankton are
the copepods  (tiny crustaceans about one millimeter long)
and fish larvae. Zooplankton are distributed according to
salinity levels. Distribution patterns also are related to those
of their main food source—the phytoplankton. Zooplankton
also feed on other paniculate  plant matter and bacteria.
   Tiny larvae of invertebrates and fish also are considered
zooplankton. Although this planktonic stage is only tempo-
rary, the larvae are a significant part of the community. These
larvae  are consumed by larger animals, and may, as they
grow, consume copepods.
   Another  group of zooplankton found in the Bay are the
protozoa. These single-celled animals feed on detritus and
bacteria. They, in turn, become food for larvae, copepods and
larger protozoa.
20    Chesapeake Bay: Introduction to an Ecosystem

-------
   Bacteria play an important function in the Bay. They are
essentially the decomposers. Their primary function  is to
break down dead matter,  particularly plants. Through this
process,  nutrients  in  dead plant and animal matter again
become available for  growing plants. Bacteria are eaten by
zooplankton and other filter-feeding animals in the Bay.
   Bacteria can be residents of the Bay or can be introduced
through  various pathways,  including human sewage and
runoff from the land.  Coliform bacteria are normal resident
bacteria found in the intestines of mammals. The presence of
coliform in a  body of water indicates that human  or other
animal wastes are present.  Coliform bacteria are an indicator
that  disease-producing pathogens  may  be present in the
water.
   Clearly visible to the unaided eye, jellyfishes and comb
jellies are the largest zooplankton. Some of these gelatinous
creatures  swim, though they are still at the  mercy of the
water currents. Jellyfishes  have tentacles with stinging cells
used to stun prey. The most famous jellyfish in the Chesa-
peake is the sea nettle. Sea nettles feed voraciously  on other
zooplankton, including fish larvae, comb jellies and  even
small fish. Because of the large volume of water in their bod-
ies, few animals except sea turtles prey on sea nettles. Comb
jellies, lacking the stinging cells of nettles, capture prey with
adhesive cells. They, too,  consume vast quantities of small
copepods and zooplankton, especially oyster larvae.

The Swimmers
   Swimmers comprise the nekton community. These organ-
isms can control and direct their movements.  This group
includes fish and some crustaceans and other invertebrates.
Approximately 350  species of  fish  can be  found in the
Chesapeake Bay.  They can be divided into  permanent resi-
dents and migratory fish. The residents tend to be smaller in
size  and do not  travel  the  long distances that migratory
species do.
   Smaller resident species, such as killifish, normally occur
in shallow  water  where they feed on a variety of inverte-
brates. The bay anchovy, the most abundant fish in the Bay,
is a key player in the Chesapeake food web. Bay anchovies
feed primarily upon zooplankton. Adult anchovies also may
consume larval fish, crab larvae and some benthic species. In
turn, the bay anchovy is a major food source for predatory
                    Bay anchovy
                 (Anchoa mitchllli)
                                               Weakfish
                                           (Cynoscion regalis)
      Striped killifish
     (Fundulus majalis)
                                  Bluefish
                            (Pomatomus saltatrix)
                                                                        Striped bass
                                                                      (Morone saxatilis)
                                                                              Living Resources & Biological Communities

-------
fish like striped bass, bluefish  and weakfish, as
well as some birds and mammals.
   Migratory  fish  fall  into  two  categories:
anadromous, which spawn in the Bay or its trib-
utaries, and catadromous fish, which  spawn in
the ocean. Anadromous fish migrate varying dis-
tances to spawn in freshwater. Some can even be
considered Bay residents. For instance, during
the spawning  season, yellow  and white perch
travel short distances from the brackish water of
the middle Bay to freshwater areas of the upper
Bay or tributaries. Striped bass also spawn in the tidal fresh-
water areas of the  Bay and major tributaries.  Some remain in
the Chesapeake to feed while others migrate to ocean waters.
Shad  and  herring  are truly anadromous, traveling from the
ocean to freshwater to spawn and returning to the ocean to
feed.  Eels are the only  catadromous species  in  the  Bay.
Although  they live in the Bay for long periods, eels eventu-
ally migrate to the Sargasso Sea in the central North Atlantic
to spawn.
   Other fish utilize the  Bay strictly for feeding. Croaker,
drum, menhaden, weakfish and spot journey into the Bay
while still in their larval stage to take advantage of the rich
supply of food. The abundance of menhaden  supports a com-
mercial fishing industry and provides food for predatory fish
and birds. Bluefish  enter the Bay only as young  adults or
mature fish.
   Besides fish, crustaceans and invertebrates may be part of
the nekton community.  Larger animals like sharks, rays, sea
turtles, and occasionally marine dolphins and whales enter
the Bay.
   The blue crab is difficult to place in any one community,
needing a  variety  of aquatic habitats, from the mouth of the
  BAY FACT
   Oysters are
    alternate
 hermaphrodites,
meaning they can
  sense gender
 imbalances and
 change their sex.
           Bay to  fresher rivers and  creeks, in order to
           complete  its life cycle. Throughout the year,
           crabs may burrow into the Bay bottom, shed and
           mate in shallow waters and beds of Bay grasses
           or swim freely in open water. The first life stage
           of a blue  crab, called the  zoea, is microscopic
           and lives  a planktonic free-floating  existence.
           After several molts, the zoea reaches  its second
           larval stage: the megalops. Another molt and a
           tiny crab  form is apparent. Both juvenile  and
           adult blue crabs forage on the bottom  and hiber-
nate there through the winter. In spring, the crab quickly
begins migrating from the southern part of the Chesapeake to
tidal rivers and northern portions of the Bay. During the rest
of the year, adult blue crabs are dispersed throughout the
Bay, swimming considerable distances using their powerful
paddle-like back fins.

Life at the Bottom

   The organisms that live on and in the bottom sediments of
the Bay  form complex communities. Known as benthos, these
bottom-dwellers include animals, plants and bacteria. Benthic
organisms often are differentiated by their habitat. Epifauna,
like oysters,  barnacles and  sponges, live upon  a  surface
Worms and clams, considered infauna,  form their  own com-
munity structure beneath the bottom sediments, connected to
the water by tubes and tunnels. The roots and lower portions
of Bay grasses supply the physical support for a variety of epi-
phytic organisms. An oyster bar,  and the many species it sup-
ports, is another example of a benthic  community. Benthic
communities that exist on or in bare, unvegetated substrate are
made up of mollusks, worms and crustaceans.
                                             LIFE STAGES OF A BLUE CRAB
          Zoea
                                               Immature
                                                 Crab
Chesapeake Bay: Introduction to an Ecosystem

-------
                                             BENTHIC COMMUNITY
A  A Hard clam (Mercenana mercenana)
B  Atlantic oyster drill (Urosalpmx cinerea)
C  Common clam worm (Nereis succinea)
D  Red ribbon worm (Micrura leidyi)
E  Soft-shelled clam (Mya arenaria)
F  Glassy tubeworm (Spiochaetopterus oculatus)  J  Oyster spat
G  Black-fingered mud crab (Panopeus herbstii)
H  Whip mudworms (Polydora ligni)
I   Sea squirts (Molgula manhattensis)
K  Ivory barnacle (Balanus eburneus)
L  Skilletfish (Gobiesox strumosus)
M  American oyster (Crassosfrea virgimca)
                   ','.".•••••.•'.•".
                  .<•<:•.    *   :-°-*-°
   As with all aquatic life in the Bay, salinity affects the dis-
tribution of bottom-dwellers, but sediment type also plays a
role. Neither coarse sand nor soft mud support rich benthic
populations. The best sediment for diverse benthic commu-
nities consists of a  mixture of sand, silt and clay.  Some
organisms  require specialized substrates. Oysters need a
clean hard surface, preferably another oyster shell, on which
the larval spat can attach or set. Oysters form a reef commu-
nity that is important habitat for other benthic species.
   The benthic community affects the physical and chemical
condition of the water and sediments. Some build tubes or
burrows  through which they pump water. Infaunal deposit
feeders,  such as worms, plow through  the sediments in
search of  food. Many benthic  animals bind  sediments
together as fecal pellets that remain at the bottom. Predators,
such as adult blue crabs, scurry across bottom searching for
food. These activities stir the sediments, increasing the rate
of exchange of materials into the water column. This mixing
also increases diffusion of oxygen  into the sediments.
                        Filter feeders, like oysters and clams, pump large volumes
                     of water through their bodies and extract food from it. As
                     they filter water for food, they also remove sediments and
                     organic matter, cleaning the  water. Since  many chemical
                     contaminants often are present in sediments, benthic fauna
                     often are exposed to and can be harmed by these pollutants.
                        Some benthic  organisms are widely  distributed. Others
                     are limited more  by salinity. For example,  hard clams and
                     oysters require higher saline waters. Mid-salinity waters sup-
                     port soft-shelled clams. Brackish water clams also are found
                     in lower salinities,  along with freshwater mussels. Salinity
                     also determines the distribution of certain benthic predators,
                     parasites and diseases. MSX, a lethal parasite, and Dermo, a
                     disease caused by another parasite, have decimated  oyster
                     populations of the mid and lower Bay, respectively. Oyster
                     drills and starfish, which feed  on oysters, are less of a prob-
                     lem in  upper Bay waters because of their intolerance  to low
                     salinities.
                                                                                Living Resources & Biological Communities

-------
                      Food  Production   &  Consumption
         The most important relationship among Chesapeake Bay
         species is their dependence upon each olher as food. We
     are all carbon-based creatures.  Carbon is the basic element
     of  organic compounds, such  as proteins,  carbohydrates,
     lipids and nucleic acids. These compounds are the building
     blocks of life that make up the bodies of living organisms.
     Feeding is the process by which organisms cycle energy-rich
     carbon through the  ecosystem. Each organism supplies the
     fuel needed to sustain other life forms.
        Plants and some bacteria can produce  their  own  food
     through a process known as photosynthesis. Using energy
     from the sun, carbon dioxide and water are combined to form
     high-energy organic compounds. These organic compounds
     and other necessary chemicals form a plant's cellular struc-
     ture, allowing it to grow. Because of this ability to use car-
     bon dioxide and sunlight to produce their own food, plants
     are called autotrophs  or self-feeders. They are the primary
     food producers. All other organisms must feed, directly or
     indirectly, on organic material produced by plants.
        Animals  cannot process  carbon  via  photosynthesis.
     Instead, they acquire  carbon by eating the organic matter
     contained in plant and animal tissue or dissolved in water.
     The animal breaks this organic material down  into com-
     ponents  it can  use for energy and growth. Animals are
     heterotrophs or other-feeders.
                     CARBON-OXYGEN CYCLE

                             Sunlight
                                                                                            BAY FACT
                                                                                             Each year,
                                                                                           cra&fars catch
                                                                                           approximately
                                                                                            two-thirds of
                                                                                           the adult blue
                                                                                          crab population
                                                                                            in the Bay.
   Every biological activity, such as reproduction, growth,
movement and bodily functions, requires energy. Whether
organisms produce food themselves or ingest it from other
sources, they all must break down organic molecules to use
the carbon and energy contained  within.  This process  is
called respiration.
   Aerobic respiration uses oxygen
and releases  carbon in the form of
carbon dioxide.  It compliments
photosynthesis, which uses carbon
dioxide and  produces  oxygen.
Together, aerobic  respiration  and
photosynthesis    compose    the
carbon-oxygen cycle.
   All  living things respire,  but
autotrophs carry out photosynthesis
as well. Plants usually release more oxygen than they con-
sume, and animals  use that excess oxygen for respiration.  In
turn, animals release carbon dioxide, which plants require
for photosynthesis.
   While carbon and oxygen are two of the most prevalent
elements in our physical make-up,  many others are needed.
Nitrogen and phosphorus  are two  such elements. They are
crucial to the operation of the Bay's life support system.
   Nitrogen is a major component  of all organisms, prima-
rily as  a key  ingredient in protein.  When an organism dies,
bacteria breaks down proteins into amino  acids. Bacteria
then remove  the carbon, converting the acids into ammonia.
Plants are able to use ammonia as a  source of nitrogen. In the
presence of oxygen, bacteria can convert ammonia to nitrite
and nitrate, also good sources of nitrogen. Under low oxygen
conditions, some bacteria convert nitrate to gaseous nitrogen
that is  unavailable  to most aquatic organisms. However,  in
tidal freshwater, some blue-green algae are able  to use
gaseous nitrogen directly.
   Phosphorus is another element essential to plant growth.
During decomposition and in the presence of oxygen, bacte-
ria convert organic phosphorus to phosphate. Phosphates are
readily used  by plants. However, phosphate also attaches to
sediment particles and settles out of water very quickly. The
resulting decrease  in available phosphorus can limit plant
growth.
   Temperature, sunlight, carbon dioxide and usable nitro-
gen and phosphorus control the rate of photosynthesis. Since
plants are the only organisms able to produce new food from
inorganic matter, the rate of photosynthesis determines the
24
Chesapeake Bay: Introduction to an Ecosystem

-------
                            FOOD CHAIN
   Producers
                       Decomposers &
                       Detritus Feeders
production of organic carbon compounds and, ultimately, the
availability of food in the Bay ecosystem.
   To illustrate how these factors affect the productivity of
the Bay, let's look at the Chesapeake's  most abundant food
producer—the phytoplankton. Like all plants, phytoplankton
require sunlight, nutrients and water. In the Bay, water is
never a limiting factor. However, the amount of sunlight and
nutrients can  limit phytoplankton growth. The amount of
sunlight available  to an aquatic plant depends on the sun's
altitude, cloud cover, water depth and turbidity (cloudiness
of water). Temperature also controls the rate of photosynthe-
sis.
   Nutrients in the form of carbon dioxide and usable nitro-
gen and phosphorus are rarely available in the exact propor-
tions required by plants. Normally, one nutrient is in short
supply compared to the others and is considered the limiting
nutrient. If a limiting nutrient is added, a growth spurt may
occur. Conversely, reducing the amount of a limiting nutrient
causes plant production to decline.
   Phosphorus controls the growth of some phytoplankton
species in the spring, especially in the tidal  freshwater and
brackish areas. Nitrogen is the prime limiting factor at higher
salinities, particularly during  warm months. Carbon dioxide
limitations may control  the  rate  of photosynthesis  during
algal blooms in tidal freshwater.
   The Bay's life support system depends on maintaining the
delicate balance between the living and non-living compo-
nents. Although  the  Chesapeake's  potential  production
capacity is massive, it is also finite. Problems affecting the
simplest producers dramatically affect the survival of con-
sumers.

The  Food Web
   As one organisms eats another, a food chain is formed.
Each step along a food chain is known as a trophic level, and
every organism can be categorized by its feeding or trophic
level. The most basic trophic  level is made up of producers:
plants and algae that make their own food. Organisms that
eat plants or  other  animals  are  consumers. Decomposers
digest the bodies of dead plants and animals and  the waste
products of both. An example of a simple food chain starts
with  phytoplankton  converting sunlight and nutrients into
living tissue. They, in turn, are eaten by copepods—members
of the zooplankton community. The copepods then are con-
sumed by bay anchovies, which are eaten by bluefish and
striped bass. These fish can be harvested and eaten by peo-
ple.  This  illustrates how organic  carbon compounds origi-
nally produced by a plant pass through successively  higher
trophic  levels.
   Food production and consumption in the Bay are rarely
this simple or direct. Seldom  does one organism feed exclu-
sively on another. Usually, several food  chains  are inter-
woven together  to form a  food web.  Decomposers appear
throughout the food web, breaking organic matter down into
nutrients.  These nutrients are again available to producers.
                                                                                       Food Production & Consumption

-------
      This complex network of  feeding  continuously  cycles
      organic matter back into the ecosystem.
        The transfer of energy from one organism to the next is,
      however, inefficient. Only about 10% of the available energy
      is transferred from one  trophic level to the next. For exam-
      ple, only a portion of the total amount of phytoplankton car-
      bon  ingested by zooplankton is  assimilated  by  the
      zooplankton's digestive  system. Some of that is used for res-
      piration, bodily functions and  locomotion. A small fraction is
      used for growth and reproduction. Since these are the only
      functions that produce additional tissue, only this fraction of
      energy is available to the consumer at the next trophic level.
        Economically important  foods like  fish  and shellfish
      depend upon lower trophic level organisms. For every pound
      of commercial fish taken from the Chesapeake, almost 8,000
      pounds of plankton had to be produced. An ecosystem must
      be enormously productive to support substantial populations
      of organisms at the highest trophic levels. Massive quantities
      of plants are required to support relatively few carnivores,
      such as the striped bass or bluefish. Because producers are
      the basis of all food, they influence the production of other
      organisms.  However, an overabundance of producers like
      algae also can be detrimental, causing a loss of Bay grasses
      and reducing the amount  of  dissolved oxygen  available to
      other organisms.
        Toxic substances in contaminated prey also can be passed
      on to the consumer. Heavy metals and organic chemicals are
      stored in the fatty tissues of animals and con-
      centrate there. As a result, an animal's body
      may contain a much higher concentration
      of the contaminant than did its food. This
      phenomenon is known as bioaccumula-
      tion. The  severe decline  of the bald
      eagle during the 1950s,  1960s and
      1970s was attributed  to  bioaccumula-
      tion. During World War II, a  chemical
      pesticide, DDT, was used to control
      insects and agricultural  pests. Fish and
      small mammals that fed on  these pests
      were in turn contaminated  with higher
      concentrations. Eagles  eating contami-
      nated prey  concentrated  even  higher   /
      levels of DDT and its by-product DDE.
      The  DDE caused the birds to lay extremely thin shells, so
      thin that most eggs broke in the nest and many eagle pairs
      failed to produce young. As a result of the DDT ban in
      1972 and  protection provided by endangered species
      status, bald eagles have been  able to recover to the pop-
      ulation we have today.
Direct and Detrital Pathways
   Two basic pathways dominate the estuarine food web.
The  direct pathway leads  from plants to lower animals to
higher animals. The detrital  pathway leads from  dead
organic matter to lower animals then to higher animals. The
detrital pathway is dominant in wetlands and Bay grass beds.
   The direct and detrital pathways coexist and are not eas-
ily separated. Higher plants, such as eelgrass, widgeon grass,
saltmarsh grass and cordgrass,  contribute most of their car-
bon  as detritus. However, epiphytic algae growing on these
grasses is usually eaten by consumers, putting them in the
direct food web.
   In deeper waters, detritus from dead phytoplankton, zoo-
plankton and larger animals, as well as detritus from upland
drainage, wetlands and Bay grasses, continually rains  down
on the benthos. Bottom-dwelling animals, such as oysters,
clams, crustaceans, tube worms, shrimp and blue crabs, feed
on it.
                               A Harpacticoid
                                 (Scottolana canadensis)
                               B Calanoid
                                 (Acart/a c/aus/j
                               C Cyclopoid
                                 (Oithona colcarva)
                                BAY FACT
                           Most larval fish consume
                               huge amounts of
                            zooplankton to survive.
                            A gallon of Bay water
                            can contain mare than
                            500,000 zooplankton.
26
      Chesapeake Bay: Introduction to an Ecosystem

-------
   The direct pathway dominates the plankton
community. The smallest  of phytoplankton,
known as nannoplankton, are fed upon by larger
microzooplankton. Larger phytoplankton,  like
most diatoms and dinoflagellates, provide food
for larger zooplankton and some fish. Bacteria,
fungi, phytoplankton and possibly protozoa pro-
vide food for oysters and clams.
   Copepods, a dominant form of zooplankton,
play a key role in the food web between phyto-
plankton and animals. Copepods feed on most
phytoplankton species and occasionally on the
juvenile stages of smaller copepods. In marine waters, most
animal protein production from plant material is carried out
by copepods. Copepods and a related organism, krill, are the
world's largest stock of living animal protein. Larger carni-
vores feed voraciously on them. Herring, for example, may
consume thousands of the tiny creatures in a single day.
   Most of the Bay's fish are part of the direct food web, but
their feeding habits are complex. Some experts contend that
   BAY FACT
Oysters were once
 so plentiful they
  could filter the
 entire volume of
  Bay water in a
  few days. This
process now takes
   aver a year.
          menhaden are the dominant  fish in the Bay's
          intricate food web. The extremely fine gill rakers
          of menhaden act  as a filtering net. Adult men-
          haden swim with  their mouths open, consuming
          any plankton in their paths. In turn, menhaden are
          a major food of striped bass, bluefish and osprey.
          They also support a large commercial fishery that
          utilizes the fish for animal feed and for products
          containing fish meal and oil.
             Like menhaden, anchovies and all fish larvae
          are primarily zooplankton feeders. Adult striped
          bass, bluefish and weakfish feed mainly on other
fish. Striped bass and other  predators also may feed upon
young of their own species. Many fish are omnivorous, eat-
ing both plants and animals. Omnivores, like eels and croak-
ers, feed on planktonic copepods, amphipods, crabs, shrimp,
small bivalves and small forage fish. Small forage fish, like
killifish and silversides, often feed upon the epifauna and
epiphytes along wetlands and in shallow water communities.
                                                                                      Food Production & Consumption
                                                                                                                    27

-------
                    Preserving  the   Chesapeake  Bay:
                    the   Big Picture
       If we want to preserve the Chesapeake Bay and its many
       delights for future generations, we must change our per-
     spectives. We must view not only what occurs in the Bay
     itself, but what happens on the land surrounding
     it. It is not enough to protect shorelines, regulate
     fisheries and  prevent direct  disposal of pollu-
     tants. We must take into account all of the activi-
     ties that occur throughout the watershed from
     Cooperstown, New York, to Virginia Beach, Vir-
     ginia, and from Pendleton County, West Virginia,
     to Seaford, Delaware. Released into this water-
     shed, fertilizers, sediment and chemical contam-
     inants from agricultural, residential and urban
     areas travel downstream to the Bay.
       However, even a watershed perspective is not
     adequate without personal responsibility. Even
     though we acknowledge that activities in  ihe  watershed
     affect the  Bay ecosystem, we must also realize that indi-
     vidual actions impact the Bay everyday:  Fertilizers and
                                            THE BAY'S
                                             FUTURE
                                            "Vihen we see
                                            the land as a
                                            community to
                                          which we belong,
                                          we may begin to
                                           use it with love
                                            and respect."
                                          Aldo Leopold,  1945
pesticides from yards and gardens affect the Bay as much as
those from large farms. Excessive use of cars produces more
exhaust with nitrogen oxides, which contribute to elevated
          nitrogen levels in the Bay. Indiscriminate use of
          water results in more water that must be treated
          and then discharged into the Bay system.
            If we want a clean, healthy Bay that can sus-
          tain biological diversity and be economically
          stable, we must identify, alter and, if possible,
          eliminate our own individual actions that impact
          the Bay. People alter ecosystems. The solutions
          to  problems threatening  the Bay are  in  the
          lifestyles we choose. The Bay ecosystem is one
          unit where forests  are linked to  oyster reefs,
          housing developments to Bay  grasses and
          choices to responsibility. Education also  is
required. Informed people choose actions that are beneficial
for  themselves, their  culture,  their  community and  the
Chesapeake Bay.
28
Chesapeake Bay: Introduction to an Ecosystem

-------
 BE  PART  OF THE SOLUTION,  NOT  PART  OF THE PROBLEM
   Reduce your nutrient input to the Bay.
   Limit the amount of fertilizers spread
   on gardens and lawns. Plant native
   vegetation that requires less fertilizer
   and water. Leave grass clippings on
   lawns and gardens. Maintain your
   septic system. Start a compost pile,
   instead of using a garbage disposal.
2
  Reduce the use of toxic materials
  around your house and yard, including
  pesticides.
  Use safer, non-toxic alternatives for
  cleaning and for controlling pests.
3
  Reduce erosion.
Plant strips of native vegetation along
streams and shorelines. Divert runoff from
paved surfaces to vegetated areas.
     ave water.
   Use water-saving devices in toilets and
   sinks. Turn off water when not in use.
   Wash cars in grassy areas to soak up
   soapy water.
                                            Drive less.
                                            Join a carpool or use public transporta-
                                            tion.
                                         6
 Obey all fishing, hunting and harvesting
 regulations.
 Be a responsible boater.
 Avoid disturbing shallow water areas and
 Bay grass beds. Pump boat waste to an
 onshore facility.
* Get involved.
 Talk to your elected officials about your
 concerns. Join or start a watershed asso-
 ciation to monitor growth and develop-
 ment locally. Participate in clean-up
 activities.
                               FOR MORE INFORMATION
                                      ABOUT THE
                                   CHESAPEAKE BAY
                                   ECOSYSTEM, VISIT
                                www.chesapeakebay. net
                                                              Preserving the Chesapeake Bay
                                                                                   29

-------
               For more information about the Chesapeake Bay and  its rivers contact:
      Chesapeake Bay Program
      (800) YOUR-BAY/(410) 267-5700
      www.chesapeakebay.net


      D.C. & STATE AGENCIES

      Chesapeake Bay Commission
      (410)263-3420
      www.chesbay.state.va.us

      District of Columbia Department
      of Health
      (202)645-6617
      www.environ.state.dc.us

      District of Columbia Public Schools
      (202)442-4016
      www.k!2 dc us

      Maryland Department of Education
      (888)246-0016
      www.msde.state.md.us

      Maryland Department of the
      Environment
      (800)633-6101
      www.mde.state.md.us

      Maryland Department of Natural
      Resources
      (410)260-8710
      www dnr.state.md.us

      Pennsylvania's Chesapeake Bay
      Education Office
      (717)545-8878
      www.pacd org

      Pennsylvania Department of
      Conservation and Natural Resources
      (717)787-9306
      www.dcnr.state.pa.us

      Pennsylvania Department of Education
      (717)783-6788
      www pde.psu.edu

      Pennsylvania Department of
      Environmental Protection
      (717)787-2300
      www dep.state.pa.us

      Virginia Department of Conservation
      and Recreation
      (804)786-1712
      www.state.va.us/-dcr/
                                       Virginia Department of Education
                                       (800)292-3820
                                       www.pen.kl2.va.us

                                       Virginia Department of Environmental
                                       Quality
                                       (800) 592-5482/(804) 698-4000
                                       www.deq.state va.us


                                       FEDERAL AGENCIES
                                       National Oceanic and Atmospheric
                                       Administration
                                       Chesapeake Bay Office
                                       (4: 0)267-5660
                                       www.noaa.gov

                                       National Park Service
                                       (4 0) 267-5747
                                       www.nps.gov

                                       Natural Resources Conservation Service
                                       (202) 205-0026
                                       www.nrcs.usda.gov

                                       U.S. Army Corps of Engineers
                                       District office in Baltimore
                                       (410)962-7608
                                       www nab usace.army mil

                                       U.S. Army Environmental Center
                                       (410)436-7113
                                       www. hqda.army.mil

                                       U.S.D.A. Forest Service
                                       (410)267-5706
                                       www.fs.fed.us

                                       U.S.  Department of Education
                                       (800) USA-LEARN
                                       www ed.gov

                                       U.S.  Environmental Protection Agency
                                       Chesapeake Bay Program Office
                                       (800) YOUR-BAY
                                       www.epa gov/r3chespk

                                       U.S.  Fish and Wildlife Service
                                       Chesapeake Bay Field Office
                                       (410)573-4500
                                       www.fws.gov/r5cbfo

                                       U.S.  Geological Survey
                                       (703)648-4000
                                       www.usgs.gov
ACADEMIC ORGANIZATIONS

Maryland Sea Grant
(301)405-6371
www.mdsg.umd.edu

Pennsylvania State University
(814)865-4700
www.psu edu

University of the District of Columbia
(202) 274-5000
www.wrlc.org/udc.htm

University of Maryland Cooperative
Extension Service
(301)405-2072
www.agnr.umd.edu

University of Maryland Center for
Environmental Science
(410)228-9250
www umces.edu

Virginia Cooperative Extension
(540)231-6704
www.ext.vt.edu

Virginia Institute of Marine Science
(804) 684-7000
www.vims.edu

Virginia Tech
(540)231-6000
www vt.edu
NONPROFIT ORGANIZATIONS

Alliance for the Chesapeake Bay
Chesapeake Regional Information Service
Hotline
(800) 662-CRIS
www acb-onhne  org

Chesapeake Bay Foundation
(410)268-8816
www.cbf org

Chesapeake Bay Trust
(410)974-2941
www.baytrust.org
30
Chesapeake Bay: introduction to an Ecosystem

-------
 Chesapeake Bay Program
THE CHESAPEAKE BAY PROGRAM
A Watershed  Partnership
   The Chesapeake Bay Program, formed in 1983 by
the first  Chesapeake  Bay Agreement,  is  a unique
regional partnership that's  leading and  directing the
restoration of the Chesapeake Bay—the largest estuary
in the United States. The Bay Program partners include
Maryland; Pennsylvania; Virginia; the District  of
Columbia; the Chesapeake Bay Commission, a tri-state
legislative body; the U.S.  Environmental Protection
Agency (EPA), which represents the federal govern-
ment; and participating citizen advisory groups. The
Bay Program's highest priority is the restoration of the
Bay's living resources—its finfish, shellfish, Bay grass-
es and other aquatic life and wildlife.
   The second Chesapeake Bay Agreement, adopted in
1987 and amended in 1992, established an overall vision
for the restoration and protection of the Bay. One of its
main goals is to reduce the nutrients nitrogen and phos-
phorus entering the Bay by 40% by the year 2000. In the
1970's, scientific and estuarine research on the Bay had
pinpointed nutrient over-enrichment as an area requiring
attention.  In the Amendments, partners agreed to main-
tain the 40% goal beyond the  year 2000  and to attack
nutrients at their source—upstream in the tributaries.
   The Chesapeake Executive Council, made up of the
governors of Maryland, Pennsylvania and Virginia; the
mayor of the District of Columbia; the EPA adminis-
trator; and the chair of the Bay Commission, guided the
restoration effort in 1993 with five directives address-
ing key areas of the restoration, including the tributar-
ies, toxic  chemicals, underwater Bay grasses, fish pas-
sages and agricultural nonpoint  source  pollution.  In
1994, partners outlined initiatives for habitat restora-
tion  of aquatic, riparian and  upland environments;
nutrient reduction in the  Bay's tributaries; and toxics
reductions, with an emphasis on pollution prevention.
                               The 1995 Local Government Partnership Initiative
                             engaged the watershed's  1,650 local governments in
                             the Bay restoration effort. The Executive Council fol-
                             lowed this in 1996 by adopting the Local Government
                             Participation Action Plan and the Priorities for Action
                            for Land, Growth and Stewardship in the Chesapeake
                             Bay Region, which  address land use management,
                             growth and development, stream  corridor protection,
                             and infrastructure improvements. A 1996 riparian for-
                             est buffers initiative furthers the Bay Program's com-
                             mitment to improving water  quality  and enhancing
                             habitat with the goal of increasing riparian buffers on
                             2,010 miles of stream and shoreline in the watershed by
                             the year 2010.  In 1997, the Bay Program renewed its
                             commitment to meet the 40% nutrient reduction goal
                             by 2000 and adopted initiatives  that addressed the
                             acceleration of current  nutrient reduction  efforts,
                             expanded wetlands protection and  support for commu-
                             nity-based watershed restoration efforts.
                               Now, the Bay Program, advisory committees, all
                             levels of government and other Bay stakeholders have
                             set their sights on Chesapeake 2000, a renewal of the
                             Chesapeake Bay Agreement and one of the four direc-
                             tives signed at the 1998 Executive Council meeting. As
                             always, the  Bay Program's highest  priority  is the
                             restoration of the Bay's living resources. Chesapeake
                             2000 will  assess the progress made since  1987 and,
                             among other objectives, will identify new science and
                             emerging  challenges related to  the Bay's health.
                             Another  directive—the  Bay Program's Education
                             Initiative—will bring information, data and the goals of
                             the Bay region's restoration into classrooms. The other
                             two 1998 directives address innovative technologies in
                             Bay restoration and regional management of the use
                             and transport of animal waste.
                                           S A 1' I  A K 1-
                                   2000
                                   The Renewed Agreement
                                CHESAPEAKE BAY PROGRAM
                           410 Severn Avenue, #109, Annapolis, MD 21403
                            1-800-YOUR BAY • www.chesapeakebay.net

-------
Striped Bass
                                                Potamogeton perfoliatus

-------