Increase in nuisance blooms and geographic
expansion of the freshwater diatom
Didymosphenia geminata:

Recommendations for response

White Paper, January 2007

Sarah Spaulding
Ecologist

Interagency Agreement with
EPA Region 8
Denver, Colorado

Leah Elwell

Conservation Coordinator
Federation of Fly Fishers
Livingston, Montana


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Foreword

In May 2006, EPA Region 8 and the Federation of FlyFishers co-sponsored an international
symposium on an emerging issue, the phenomenon of Didymosphenia geminata. A concerned
group of international scientists, resource managers, aquatic professionals, conservation groups,
consulting firms, and state, federal and tribal agencies gathered to bring together the current
knowledge of this microscopic diatom. The meeting was exceptional for the diversity of interests
of participants, all joined by a common concern about a rather small organism, and its behavior
and potential impacts. This white paper is an outcome of that meeting and the expressed need by
participants to document the issues and make recommendations in responding to the change in
behavior of D. geminata. We hope this document provides a basis to address research and
management needs and to stimulate understanding of an amazing biological phenomenon.

Endorsement

This document has been endorsed by:

Dave Beeson

ENVIRON International Corp.
Denver CO

Black Hills FlyFishers

Rapid City, SD

Dr. Max Bothwell

Environment Canada
British Columbia, Canada

Dr. Michael Gretz

Michigan Technological University
Houghton, MI

Dr. Ingi Runar Jonsson

Institute of Freshwater Fisheries
Iceland

Tim Kacerek

Central Arizona Project
Phoenix, AZ

Dr. Martyn Kelly

Bowburn Consultancy
Bowburn, United Kingdom

Dr. Andrea Kirkwood

University of Calgary
Alberta, Canada

Aaron Larson

Environmental Program Specialist
South Dakota Dept. of Environment
and Natural Resources
Rapid City, SD

Dr. Kris McNyset
Ecologist
Corvallis, OR

Gary Lester

President
EcoAnalysts, Inc.

Moscow, ID

Matt Miller

Institute of Arctic and Alpine
Research

University of Colorado
Boulder, CO

Jenifer Parsons

Aquatic Plant Specialist
Washington Dept. of Ecology
Yakima, WA

Peter Pryfogle

Algologist

Rithron Associates

Missoula, MT

Travis Schmit

USDA National Needs Fellow in
Natural Resources
Colorado State University
Fort Collins, CO

Matt Schroeder

Arkansas Fish and Game
Commission

Jeff Shearer

Coldwater Fisheries Biologist
South Dakota Game, Fish & Parks
Rapid City, SD

Kevin Sloan

Fishery Research Biologist
US Fish and Wildlife Service

Dr. Christina Vieglais

Senior Advisor
Biosecurity New Zealand
Wellington, New Zealand

Harlan Wright

Fisheries Technician
BC Conservation Foundation
British Columbia, Canada

Disclaimer

The views expressed in this paper do not necessarily represent those of the US Environmental
Protection Agency. In addition, although the research described in this paper may have been
funded in part by the US Environmental Protection Agency, it has not been submitted to the
Agency's required peer and policy review. No official Agency endorsement should be inferred.


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Research and management response to D. geminata Page 3

Executive Summary

The diatom Didymosphenia geminata (Lyngbye) Schmidt is emerging as an organism with an
extraordinary capacity to impact stream ecosystems on a global scale. In recent years, streams in
New Zealand, North America, Europe, and Asia have been colonized by unprecedented masses of
"didymo" and its extracellular stalks. This diatom is able to dominate stream surfaces by covering
up to 100% of substrate with thicknesses of greater than 20 cm, greatly altering physical and
biological conditions within streams. This species is expanding its geographic range in North
America and the rate that nuisance blooms are reported by the public and local media are
increasing, yet little scientific investigation of the phenomenon in North America has been
initiated.

Figure 1. A. Image ofD. geminata cell under the light microscope. Scale bar is equal to 10 microns. B. Cobble from
stream showing typical growth habit. Scale bar is approximately 10 cm. C. Map showing the continued distribution
records ofD. geminata in North America.

Problem

A global community of scientists, land managers, and anglers have reached consensus views on
realized and potential threats o/ Didymosphenia geminata We recognize a growing body of
evidence that D. geminata is:

•	the only freshwater diatom to exhibit large scale invasive behavior, and a persistent
phenomenon on a global scale

•	a species with the biological capacity to produce inordinate amounts of stalk
material (extracellular mucopolysaccarides) with unique properties

•	a significant biological impact to stream ecosystem function, with the ability to alter
foodweb structure and hydraulics of streams and rivers

•	an organism that has expanded its ecological range and tolerance

•	exhibiting a pattern of growth with potential impact to fisheries

•	a significant strain on regional and national economies through impacts to tourism,
fisheries, and hydropower

•	an organism for which we lack basic biological and ecological knowledge


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Summary of Recommendations

•	Develop an aggressive education and outreach program to change user behavior in
order to minimize spread of D. geminata on a global scale.

•	Determine if there has been a genetically based physiological change in D. geminata
that is linked to a nuisance strain.

•	Trace the relationships of nuisance outbreaks and those records can be compared
with models of predicted global distribution using molecular markers.

•	Determine the degree to which the spread of D. geminata is aided by specific human
vectors on waders or other gear.

•	Track the geographic distribution of D. geminata on a global scale using effective
and proper documentation of sites and voucher material.

•	Determine the ecological conditions under which excessive biomass is produced in
low nutrient streams and rivers, over short periods of time.

•	Develop strategies to mitigate existing blooms.

•	Determine the unique composition, structure, and cellular processes that produce the
D. geminata stalk, which is responsible for its negative ecosystem impacts.

•	Determine it perturbations in signal, regulatory, and/or synthetic pathways of stalk
production by cymbelloid diatoms has resulted in increased production in D.
geminata.

•	Evaluate the apparent resistance of the stalk to degradation by bacteria and fungi,
and determine ecosystem effects of stalk material.

•	Verify the direct and indirect impacts ofD. geminata and its stalks to aquatic
macroinvertebrates and fish.

•	Resolve the impacts of D. geminata at both high and low densities and whether there
are threshold levels of nuisance growths.


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Table of Contents

Foreword		2

Introduction		6

Biology		6

Geographic Distribution		8

North America
Europe
New Zealand

Global view of suitable stream habitats

Ecological Relationships	 11

Stalks responsible for high biomass
Nuisance blooms
Stalk legacy

Interactions with invertebrates
Interactions with fish
Water chemistry
Hydraulic range
A biological paradox
Molecular markers

Range Expansion		19

Economic Impact		20

Control techniques		20

Reduce the Spread		20

Summary		21

Recommendations		22

References		24

Acknowledgements		28

Appendices		29

Appendix A: Additional Resources
Appendix B: Scientific Meetings
Appendix C: Glossary
Appendix D: Media coverage


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Research and management response to D. geminata Page 6

Introduction

Didymosphenia geminata (Lyngbye) Schmidt was originally described from the Faroe Islands,
north of Scotland. This diatom was very common in Scotland, Sweden and Finland (Cleve 1894-
1896) and in the Kanchou region of China, D. geminata formed massive accumulations
(Skvortzow 1935). While historic growth patterns include episodic formation of large masses,
grow th patterns now differ by having greater spatial coverage and temporal persistence. Until
recently, this diatom was restricted to low nutrient waters, but now it occurs in more nutrient-rich
streams and rivers. In many regions of North America, D. geminata now forms nuisance benthic
growths that extend for greater than 1 km and persist for several months of the year. Furthermore,
D. geminata has appeared to expand its geographic range within North America and Europe and
recently invaded New Zealand. Under nuisance bloom conditions, D. geminata cells produce
copious amounts of extracellular stalk material that form thick benthic mats. To the observer,
these mats appear as fiberglass insulation, tissue paper, "rock snot", brown shag carpet, or sheep
skins covering the streambed (Fig.2).

FIGURE 2. A. Stream cobble covered withZ). geminata and stalks 5 cm thick. Scale bar equal to approximately 10 cm. B. Streambed
covered withZ). geminata. Note that rocks and cobbles are hardly visible. Scale bar equal to approx. 10 cm. C. Dried stalks on docks.
(Images by Erica Shelby, Arkansas Department of Environmental Quality).

Biology

Didymosphenia geminata is a diatom, which is a type of
single-celled algae. Diatoms are remarkable organisms, unique
for their silica (Si02) cell walls, which are often well-
preserved in sediments making diatoms useful as
environmental indicators (Smol & Stoermer 1998). Diatoms
are found in nearly every freshwater and marine aquatic habitat
and contribute a large percentage of the global carbon budget
through photosynthesis. In both oceans and freshwaters,
diatoms are one of the major groups of organisms within the
plankton (including other algae, bacteria, and protozoa) and
also grow attached to surfaces. Diatoms store chrysolaminarin
(B1.3 linked glucan) as well as accumulate lipid within the cell.
Lipids are an oil-rich source of energy, which make diatoms a
valuable food for other organisms. The life history of diatoms
includes both vegetative and sexual reproduction (reviewed in
Edlund & Stoermer 1997), although the sexual stage has not
been documented in D. geminata (but see Skabichevsky 1983).

FIGURE 3. Scanning electron micrograph of the silica cell wall of D. geminata. The raphe is composed of the two slits that run along
the apical axis of the cell. The cell secretes mucopolysaccarides through the raphe in order to move on surfaces. At the base of the cell
is the porefield, through which the stalk is secreted. Scale bar equal to 50 pm (Image by Sarah Spaulding, US Geological Survey).


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Research and management response to D. geminata Page 7

FIGURE 4. Scanning electron micrograph of D. geminata cells and their mucopolysaccaride stalks. The stalks produced within the cell
are many times the length of the cell itself. Note the smaller diatoms growing attached onto the stalks. Scale bar equal to 100 jim
(Image by Sarah Kiemle, Michigan Technological University).

Valve morphology of the genus Dldymosphenia has been well documented (Dawson 1973a,
1973b. Antoine & Benson-Evans 1983, Stoermer et al. 1986, Metzeltin & Lange-Bertalot 1995).
Dldymosphenia is considered within the cymbelloid, rather than gomphonemoid, lineage of
diatoms (Kociolek & Stoermer 1993). Cells possess a raphe, a structure that allows the cells to
move on surfaces. The cells also possess an apical porefield, through which a mucopolysaccaride
stalk is secreted (Fig. 3). The stalk may attach to rocks, plants, or any other submerged substrate.
When the diatom cell divides (i.e. vegetative reproduction), the stalk also divides, eventually
forming a dense mass of branching stalks. It is not the diatom cell itself that is responsible for the
negative impacts of D. geminata, but the massive production of extracellular stalk (Fig. 4).

50
45
40
35
30

I

i 25
sS

20
15
10
5
0

FIGURE 5. Biochemical composition of three fractions of the D. geminata stalk (hot water soluble, EDTA soluble, EDTA insoluble).
The three fractions differ in their percentage composition of urionic acid, sulfate compounds, carbohydrate, and protein (Data from
Michael Gretz, Michigan Technological University).

¦

¦

J



H Proten

Carbohydrate
¦ Sulfate
m UromcAcd

HW soluble EDTA sol EDTA insoluble


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Extracellular polymeric substances (EPS) that comprise the stalk are predominantly composed of
polysaccarides and protein (Fig. 5). They are complex, multi-layered structures that are resistant
to degradation. The degree to which internal (genetic) and external (environmental) change
initiates the high level of stalk production is unknown, yet resolving the mechanisms of stalk
production is crucial for determining ecological impacts, physiological regulation, and control of
D. geminatct. We have little understanding of the biology and ecological roles of D. gemincita,
and we need basic information to determine the causes and conditions that lead to nuisance
blooms and the geographic expansion of this diatom. Hie first step is to determine the signal and
regulatory genes in D. gemincita that may be activated in response to environmental cues to result
in excessive stalk production. Other cymbelloid diatoms produce stalks that are close in chemical
composition to D. gemincita. These species (notably varieties of Cymbellct mexicanct) may also
produce excessive amounts of stalks, leading to nuisance growths.

Geographic distribution

North America

In North America, historical reports of D. gemincita are sparse and voucher specimens are
uncommon. Although it is not possible to state the historical range of this diatom with
confidence, historical distributions were considered to be northern circumboreal in cold,
oligotrophic waters. The earliest published records of D. gemincita from North America on
Vancouver Island, British Columbia (Cleve 1894-1896); however there are no notes on its
abundance. Nearly one hundred years later, D. gemincita formed nuisance blooms m the Heber
River and over a period of five years had spread to twelve other watersheds on Vancouver Island
(Sherbot & Bothwell 1993, Bothwell et al, 2005).

-120	-110	-100	-90	-80	-70

FIGURE 6. Confirmed presence and absence records of D. geminata in the United States. A total of 4569 samples were included and
D. geminata is present in 283 sites. Records are based on data from USGS National Water Quality Assessment (NAWQA), EPA
Environmental Monitoring and Assessment (EMAP), and samples from other studies. (Map by Sarah Spaulding, US Geological
Survey).


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Research and management response to D. geminata Page 9

Since that time, nuisance blooms have waned, but the diatom is present in more streams. In The
Diatoms of the United States, Patrick & Reimer (1975) reported only one state, Virginia, as the
distribution for D. geminata in the United States. More recent works consider D. geminata as
present in rivers in the western United States (Bahls 2004). A pattern of expanding range and
nuisance populations has developed in North America over the past several years (Fig. 6)
(Pryfogle et al. 1997, Holderman & Hardy 2004, Shelby 2006), as well as in Europe and New
Zealand (Fig. 7).

Europe

In European countries, reports are variable concerning the extent of D. geminata in streams and
rivers. Northern and western rivers of the United Kingdom are subject to large masses of A
geminata, but the growths are considered to be a natural phenomenon and have been recorded for
over 150 years. There are no reports of geographic expansion or increase in biomass of D.
geminata (Whitton & Crisp 1984). Likewise, although masses of D. geminata increased with
regulation of streamflow (Skulberg 1982), the formation of blooms is considered a normal event.

In Icelandic rivers, D. geminata fonned large blooms beginning in the early 1990 "s (Jonsson et
al. 2000). Blooms had no relation to bedrock geology or specific conductance, that is, the
distribution and biomass of extensive mats appeared to be unrelated to water chemistry. Since the
1990 "s. populations of D. geminata have decreased, or remained stable. Icelandic rivers are vital
to the salmon fishery and there was concern that the masses of D. geminata would negatively
impact spawning, yet there is no clear evidence of a negative influence of D. geminata on fish
stock.

FIGURE 7. Confirmed presence and published records of D. geminata from around the world. Dots do not represent number of
reports, but show rough geographic area of populations. (Map by Sarah Spaulding, US Geological Survey).

Pligh abundances of D. geminata were documented in several rivers of the Carpathian, Gorce, and
Tatra mountains of Poland (Kawecka & Sanecki 2003, Noga 2003). Observations of extensive
growths and their expansion to new watersheds was contrasted to observations from the 1960"s
when D. geminata was present, but occurred in low abundance. The rivers where D. geminata
formed large masses in recent years are impacted by anthropogenic nutrient input, with river


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Research and management response to D. geminata Page 10

concentrations of nitrate (N03) ranging from 1.7 to 3.8 mg/1 and phosphate (P04) ranging from
13 to 100 Lig/1 (Kawecka & Sanecki 2003). The discovery of nuisance D. geminata populations in
high nutrient waters was the first recognition that the species was appearing outside its recognized
ecological range.

Similar to rivers in Poland, the eutrophic Tisa River in Serbia was reported to contain D.
geminata throughout most of the year (March through November) (Subakov-Simic & Cvijan
2004). The Tisa River had temperatures above 20 °C for three months of the year, as well as high
concentrations of ammonia (NH3) (0.67 mg/1) and metals. This report also presents evidence that
D. geminata is able to grow well at high temperatures and in polluted sites. Such a finding is
repeated in the Degirmendere River in Turkey, where irrigation return flows, municipal wastes,
and other inputs heavily influence water chemistry (Kara & Sahin 2001). At this site, D. geminata
was found in high abundance for several months of the year.

New Zealand

The first confirmed record of D. geminata in the southern hemisphere was in October of 2004, in
the lower Waiau River of the South Island of New Zealand (Kilroy 2004). Despite a proactive
response of containment by the New Zealand government, within 18 months D. geminata spread
to 12 rivers on the South Island (Fig. 8) and formed excessive blooms in several sites. The
blooms in New Zealand demonstrate that D. geminata is an aggressive invasive species with
dramatic ecological, economic, social, hydropower, recreational, and aesthetic impacts (Kilroy et
al. 2005a, 2005b, 2005c, 2006, Campbell 2005, Branson 2006).

FIGURE 8. Confirmed presence of D. geminata in New Zealand as of July 2006.

Biosecurity New Zealand, the branch of government responsible for invasive species, identified
D. geminata as harmful and of great concern. There is widespread agreement that D. geminata


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Research and management response to D. geminata Page 11

was introduced through human activity, in fact, penalties of up to five years imprisonment and a
fine of $100,000 NZ are in place for intentionally spreading D. geminata. As ofNovember 2006,
D. geminata has not been confirmed in any locations on the North Island of New Zealand.

Prior to the incursion in New Zealand, knowledge of ecosystem roles and impacts of D. geminata
was primarily anecdotal (Kilroy 2004). At the present time, several scientific and technical
studies have been completed, or are in progress to address identification, detection, distribution,
containment, impact, and control or eradication of D. geminata in New Zealand (see Appendix A
for Biosecurity NZ website). As a result of work in New Zealand, the ability of D. geminata to
survive outside water and requirements to decontaminate aquatic gear from live cells has been
experimentally established. The range of D. geminata in terms of hydraulic habitat, temporal
changes in biomass, and relation to density of benthic invertebrates has been investigated (Kilroy
et al. 2005d). The interaction of flows and the likelihood of D. geminata transport to vital
hydropower sites in Lake Manapouri were established (Biggs et al. 2005, Sutherland et al. 2005).
Studies to determine the effects of D. geminata on native fish and invertebrates (benthic and drift)
and water quality (dissolved oxygen and pH) are in progress. Other studies will address impacts
of D. geminata on productivity of trout, develop molecular detection methods, and establish
efficient monitoring efforts.

Global view of suitable stream habitats

A global distribution map based on ecological niche models shows suitable stream habitats for D.
geminata on every continent except Antarctica (Fig. 9) (McNvset & Julius, 2006). While
historical records in North America are poor, this map presents very different picture from the
distribution of D. geminata (given in the United States as Virginia) (Patrick & Reimer, 1975). We
now know that D. geminata can thrive in a wide range of physical and chemical conditions within
rivers and spread by humans is of concern. Rivers in the southern hemisphere are particularly at
risk to new introduction and invasion. Appropriate agency personnel in Australia, Argentina,
Chile and Peru should be notified and made aware of the potential ecological damage and
urgency of implementing decontamination procedures.

FIGURE 9. Map of the world showing regions where suitable stream habitats for D. geminata are located. Results for Australia are
preliminary (Map by Kris McNyset, US Environmental Protection Agency).

Ecological relationships

The physical, chemical, and biological properties of streams and their organisms are intimately
tied (Hynes 1975). Didymosphenia geminata both influences the stream environment and is
controlled by environmental features. This diatom is capable of producing such great amounts of


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Research and management response to I). geminata Page 12

stalk that the mats covering the stream bed result in changes in ecological properties of the stream
(e.g., species diversity, population sizes, nutrient pools) (Larned et al. 2006). Algal, invertebrate,
and fish species diversity and population sizes may be altered. In addition, high growth rates and
extensive mats of D. geminata may impact ecological processes such as ecosystem metabolism
and nutrient cycling. Stalk and algal biomass, formation of nuisance blooms, legacy of stalks,
interactions with invertebrates, interactions with fish, control by water chemistry and hydrology,
impact on dissolved oxygen, and seasonal cycles are all part of how this organism exerts its
influence on its stream and how it is also controlled by environmental features.

Stalks responsible for high biomass

A comparison of D. geminata biomass as ash free dry mass (AFDM) and chlorophyll a confirms
that the mats are accumulations of stalks with a thin surface layer of cells (Larned et al. 2006).
The AFDM biomass of D. geminata was measured to be 250 times greater than the chlorophyll a
biomass. The comparison also indicates that the ecological interactions related to D. geminata are
primarily due to the impact of the extracellular stalks, not the cells themselves. Blooms of D.
geminata generate biomass and chlorophyll values many times those found in non-bloom
conditions. Furthermore, AFDM biomass is produced at a level considered indicative of a
biologically impaired river. In New Zealand rivers, an analysis of AFDM and chlorophyll a
exceeded national guidelines for pcriphyton biomass (Table 1) (Kilroy et al. 2005a). The
guidelines are intended to maintain high quality angling and fish habitat, and values are much
higher than in non-D. geminata streams in New Zealand and elsewhere.

Table 1. Minimum and maximum ash free dry mass (AFDM) and chlorophyll a (Chi. a) for periphyton cover from
studies in New Zealand rivers. Sites with large masses of D. geminata are shown in bold text. (Data from Kilroy et al.
2005a).

River

AFDM(g/m2)

AFDM(g/m2)

Chi. a (mg/

Chi. a (mg/

Reference



min.

max.

m2) min.

m2) max.



Mararoa

18

1171

145

1029

Kilroy et al. 2005a

Lower Waiau

34

210

157

1155

Kilroy et al. 2005a

Ohau

10

63

~2

-55

Biggs & Hickey 1994

Quebec streams

2.4

22.6

5.1

54.6

Bourassa & Cattaneo 1998

Mataura

-2.5

45

-

-

Biggs et al. 1998

Waiau

-

-

-0.3

-200

Biggs et al. 1998

Nuisance blooms

Although D. geminata occurs in both lakes and flowing waters, nuisance blooms are only known
in streams and rivers. In contrast to historical, episodic growths of D. geminata, nuisance blooms
are masses of cells and stalks that extend for greater than 1 km and persist for several months of
the year. During a nuisance bloom, D. geminata cells produce copious amounts of extracellular
stalk material.

For the purposes of this document, the phrase "nuisance bloom" refers to growths in sites where
D. geminata was considered within its native range (northern boreal and high elevation sites), but
where benthic mats are extensive spatially and temporally (Table 2). For example, nuisance
blooms in Rapid Creek, South Dakota are present over a 5 to 10 km reach, at 30 to 100%
coverage, for over 4 months of the year and are recurring. "Invasive blooms" refer to appearance
of D. geminata in locations with no previous record (e.g., New Zealand) and denotes the behavior
of an introduced non-indigenous species.


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Table 2. Some of the rivers in North America with documented nuisance blooms. The list is likely to be much more
extensive. Documenting the occurrence and extent of blooms is problematic based on existing monitoring efforts
because measurements may not be made at the appropriate spatial scale.

Province/State River	Years	Reference

Alberta

Red Deer

Late 1990's

A. Kirkwood, U. Calgary



Bow





Arkansas

Red

2005

Shelby 2006



White





British Columbia

Heber

1985

British Columbia, Ministry of



Englishman

1993

Environment



Nahmint

1995-1997





Stamp/Somass

1993,95,96,01,02





Puntledge

1997,02,03



California

American Fork

Mid 1990's

S. Spaulding, US Geological Survey







S. Lehr, California Dept. Fish &







Game

Montana

Kootenai

2001-?

Holderman & Hardy 2004

Tennessee

Clinch

2005

T. Baker, Tennessee Valley



South Holston



Authority

South Dakota

Rapid Creek

2002

J. Shearer, South Dakota Dept of







Game Fish & Parks

Virginia

Jackson

2006

S. Smith, Virginia Dept. of Game



Smith

2006

and Inland Fisheries

In a broad sense, nuisance algal blooms are typically directly related to anthropogenic increases
in nutrient input to surface waters (Schindler 1977, Anderson et al. 2002). Increased
concentrations of nitrogen and phosphorus result in adverse effects due to excessive primary
production of algae. Cyanobacterial (blue-green algae) blooms are a well-known phenomenon in
freshwater with high quantities of phosphorus (Jacoby et al. 2000, Bowling 1994, Hecky &
Kilham 1988). In contrast, blooms of D. geminata are unlike other algal blooms, because they are
associated with nutrient-poor waters. Notably, many D. geminata blooms have occurred in stream
habitats generally considered pristine or with limited ecological disturbance (Jonsson et al. 2000,
Sherbotand Bothwell 1993).

In North America, documenting the occurrence and extent of D. geminata is problematic.
Standard counting techniques for diatom analysis underestimate the presence of D. geminata in
the western United States by at least 50% (S. Spaulding, U.S. Geological Survey unpublished
data). Compared to other diatom species, D. geminata has much larger cells (80-150 |im in
length); yet smaller cells dominate the diatom community (Fig. 10). Counting procedures
intended to evaluate diatom species in the periphyton are often based on a fixed count (e.g., 300
cells counted), which favor small, numerous species. An alternative technique is to note the
presence of D. geminata cells, even if they do not appear in standard analysis. Interestingly, D.
geminata never comprises greater than 3% of the diatom community in western streams (EPA
Environmental Monitoring and Assessment Program data), even within samples collected from
nuisance blooms. Reports of data using biovolume avoid part of the problem (Jonsson et al.
2000), by reporting abundance in terms of biomass, rather than number of cells.

A measure such as the visual biovolume index (Kilroy et al. 2005d) is a preferred method to
estimate the abundance and impact of D. geminata. The visual biovolume index is a measure of


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Research and management response to D. geminata Page 14

the percent coverage of D. geminata on a cross section of stream channel, multiplied by the
thickness of the mat. The index takes the amount of extracellular stalk into account and is more
appropriate for documenting the extent of nuisance blooms. In order to track the geographic
distribution of D. geminata on a global scale, it is important to use effective and proper
documentation of sites and archive voucher samples.

V V

FIGURE 10. Microscope image of diatoms showing relative size of cells. Didymosphenia geminata is underestimated in terms of
presence because standard counting techniques are directed at small species. (Image by S. Spaulding, U.S. Geological Survey).

Legacy of stalks

The extracellular stalk of I), geminata is a complex, multi-layered structure, resistant to
degradation in streams. Observations in Colorado streams show that stalks persist up to 2 months
following a peak in growth of D. geminata (S. Spaulding, U.S. Geological Survey unpublished
data). In effect, the stalks persist in the stream longer than the cells that produced them (Fig. 11).
Furthermore, the stalks trap fine sediment within their dense matrix and change the nature of the
stream substrate. This coating of the stream benthos may then act to control the algae and
invertebrate species able to feed and move on those surfaces. The legacy of the D. geminata
stalks is a potentially strong influence on stream community composition. It is important to
evaluate the apparent resistance of the stalk to degradation by bacteria and fungi, and determine
ecosystem effects of stalk material.

FIGURE 11. Image of a rock coated withZ). geminata stalks and fine sediment. The cells of the diatom are no longer present, but the
stalks continue to determine the nature of the stream substrate. (Image by S. Spaulding, U.S. Geological Survey).

Interactions with invertebrates

Abundance and diversity of benthic macroinvertebrates are likely to be affected by D. geminata
in two ways: direct trophic interactions and habitat interactions (Lamed et al. 2006). Direct
trophic interaction refers to utilization of D. geminata as a food source. Macroinvertebrate species
that consume D. geminata are expected to be favored over those species that don't eat D.
geminata. Habitat interaction refers to utilization of stream surfaces by macroinvertebrates.


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Species that require exposed sediment are expected to be negatively impacted by extensive
coverage of D. geminata. Recent work in New Zealand, Colorado, and Montana indicates that
there are complex interactions between D. geminata and benthic macroinvertebrates.

Results from New Zealand rivers indicate that both number of species and density of
invertebrates was greater with higher D. geminata coverage (Larned et al 2006). However, few of
the species present were characteristic of high river health. With lower amounts of D. geminata
coverage, invertebrate abundance and diversity increased, forming a more even distribution of
species within the community. In contrast, results from Colorado rivers indicate that high
densities of D. geminata were related to a decline in total macroinvertebrate richness (T. Schmidt,
personal communication). In these rivers, the macroinvertebrate community was dominated by
chironomids (midge fly larvae). Analysis of macroinvertebrate gut contents showed that mayfly,
stonefly, caddisfly, and chironomid larvae consumed D. geminata, but that the presence of D.
geminata in guts was related to body size. That is, the results suggest that small
macroinvertebrates were not able to consume D. geminata. Results from surveys in Montana (D.
Beeson, personal communication) showed dramatic increases in D. geminata cover (up to 100%
over monitoring period of 1998-2003). This study also indicated an increase in diptera taxa
(including midge fly larvae) and loss of mayflies, stoneflies, and caddisflies.

These initial results suggest that the impact of D. geminata on aquatic macroinvertebrates is
directly related to temporal and spatial extent of nuisance blooms. If D. geminata masses are
capable of altering the taxonomic composition and size of benthic macroinvertebrates present in
the drift, that relationship represents a trophic level impact. Further work should resolve the
differences in impacts of D. geminata at both high and low densities and whether there are
threshold levels of nuisance growths. In addition, it would be beneficial to determine the extent to
which macroinvertebrate grazing reduces D. geminata abundance. An open question is the degree
to which macroinvertebrates are physically able to move through the masses of stalks to gain
access to the nutritious cells.

Interactions with fish

Studies on the effects of D. geminata on native New Zealand fish are in progress (Larned et al.
2006). Given large amounts of non-nutritious stalk material present on stream substrates in
affected areas, D. geminata is predicted to have deleterious effects on native fish. Fish that inhabit
benthic habitats, consume benthic prey, and nest beneath or between cobbles are expected to be
the most impacted because they utilize the same habitat as D. geminata (Larned et al. 2006).
Nuisance growths of D. geminata have the potential to impact fisheries through food web
interactions with aquatic macroinvertebrates. That is, if the favored food sources for fish are
impacted in a negative way, fish will also be impacted negatively.

Water chemistry

Water chemistry is typically considered a controlling factor for diatom distribution and
abundance, particularly nutrient concentrations and pH. Historically, D. geminata was considered
to be restricted to oligotrophic (low nutrient) and low temperature waters, and a broad range of
conductance in the European Alps (Krammer & Lange-Bertalot 1986). Although historical values
of chemical and physical parameters in relation to D. geminata biomass were not recorded, there
is a widespread understanding among diatomists and aquatic ecologists that D. geminata had
narrow environmental tolerances. Therefore, one of the commonly noted observations about this
diatom is the expansion of its ecological tolerance to a broader physical and chemical range
(Kawecka & Sanecki 2003, Kilroy 2004).


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Research and management response to D. geminata Page 16

Preliminary data from a random survey of streams in the western United States (Stoddard et al.
2005) show that D. geminata is present in a wide range of freshwater conditions (Fig. 12). These
data are presented based on presence/absence of D. geminata in the western Environmental
Monitoring and Assessment Program (EMAP) pilot. Rather than being restricted to cold
temperatures, D. geminata is present m waters from 4 to 27 °C, and shows a temperature range
greater than what was previously observed. The relation of D. geminata presence to pH is narrow,
with D. geminata found in waters at, or above, a pH of 7.

0	5	10	15	20	25	30	6.0	6.5	7.0	7.5	8.0	8.5	9.0

degrees C	pH

Figure 12. A) Water temperature versus frequency of sites withD. geminata present in western streams of the United
States. B) pH versus frequency of sites with D. geminata present. (Data from EPA EMAP Western Pilot for 2000-
2003.)

The range of specific conductance and acid neutralizing capacity (ANC) at sites with D. geminata
present are both broad (Fig. 13). These data demonstrate a wide range of tolerance from
electrolyte poor to concentrated waters, although D. geminata occurs more often at lower values
of conductance and ANC.

0 100 200 300 400 500 600 700	0	1000 2000 3000 4000 5000 6000

condictance (umho/cm)	ANC

Figure 13. A) Conductance ((.unlio/cm) versus frequency of sites with D. geminata present in western streams of the
United States. B) Acid neutralizing capacity (ANC) versus frequency of sites withD. geminata present. (Data from
EPA EMAP Western Pilot for 2000-2003.)

Although D. geminata occurs most frequently in waters with low total phosphorus (< 2 ug/1) and
low nitrate (< 1 mg/1) (Fig. 14), it can also be found where both of these nutrients are present at
very high concentrations. These values show where D. geminata is present, but give no indication


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Research and management response to D. geminata Page 17

of the biomass or growth rate in association with nutrient concentration. Furthermore, it is
unknown if D. geminata is limited by either of these important nutrients in any streams in North
America. In New Zealand, nutrient enrichment experiments indicate that growth of D. geminata
is limited by nitrogen, phosphorus, or both nutrients within most of its current range (Larned et al.
2006). In other words, with greater concentrations of either nutrient growth would be stimulated.
Increased loading of nutrients to affected rivers by watershed sources is expected to result in
increased growth of D. geminata.

Figure 14. A) Total phosphorus (jj.g/1) versus frequency of sites withD. geminata present in western streams of the
United States. B) Nitrate (mg/1) versus frequency of sites withD. geminata present. (Data from EPA EMAP Western
Pilot for 2000-2003.)

Hydraulic range

Didymosphenia geminata thrives in a wide range of hydraulic conditions (Fig. 15) (Kilroy et al.
2005c). The hydraulic range is striking, because dense mats of the alga are able to grow in slow
moving, shallow waters as well as waters with greater depth and velocity than could be safely
measured by technicians. In the Mararoa and Waiau rivers, masses of D. geminata were greatest
at water velocities of approximately 0.5 m/s. With stable flow, biomass of D. geminata tends to

500 r- •

400

300

200

100

0

_L

• *

J	I	

_L

0.0 0.3 0.6 0.9 1.2
Water velocity at 0.6 depth (m/s)

1.5

Figure 15. Water velocity versus visual biovolume index in the Mararoa River, New Zealand. The pattern indicates
there is no relation between water velocity and visual biovolume index. Didymosphenia geminata forms dense mats
(high visual biovolume index) from low to high water velocities. (Data from Kilroy et al. 2005c).


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Research and management response to I). geminata Page 18

increase. In fact, the best hydrological predictor of D. geminata biomass is number of days since
a flood greater than 75 to 100 m3/s. In other words, large floods scour the river bed and return
biomass to a low level. However, in order to reduce cell biomass, floods must be high enough to
cause the rocks on the streambed to mobilize (Larned et al. 2006), scouring the cells from rock
surfaces.

In North America and Europe, high density blooms are frequent in rivers directly below
impoundments (Skulberg 1982, Dufford et al. 1987, Kawecka & Sanecki 2003). A monthly
survey of rivers in Alberta, Canada suggests that D. geminata occurs with higher frequency in
locations where flow and temperature is regulated by dams compared to non-regulated rivers (A.
Kirkwood, University of Calgary, personal communication). In these river reaches, stable flows
and fairly constant temperatures favor development of large masses of D. geminata. Restoration
of historic, or pre-impoundment, natural flows in rivers may mitigate nuisance blooms, as well as
restore river condition.

A biological paradox

Recent work on D. geminata blooms has resulted in a remarkable observation. Within the masses
of extracellular stalks and cells, concentrations of dissolved oxygen are supersaturated with
respect to the atmosphere (Larned et al. 2006). Determining the source of nutrients and flux of
oxygen within the algal mats is likely to reveal how D. geminata attains its remarkable biomass.
Typically, the concentration of dissolved oxygen within algal mats formed by other species is not
supersaturated, but oxygen concentrations may be quite low as cells respire and decompose. In
contrast, peak values of dissolved oxygen are present well below the surface of the D. geminata
mats. Larned et al. propose that these algal mats contain other photosynthetic organisms that are
actively producing oxygen. They suggest that a unique assemblage of organisms is able to utilize
high concentrations of dissolved nutrients produced in organic matter at the bases of mats, and
then transfers these nutrients to D. geminata cells. An investigation of the processes within the
mat matrix will lead to addressing the biological paradox of how D. geminata produces excessive
biomass in low nutrient streams and rivers, over short periods of time.

Molecular markers

Craig Cary, University of Waikato, New Zealand is leading an effort to elucidate a genetic
marker that allows a quick, inexpensive, and reliable method for determining the presence of I),
geminata within a watershed. The Cary laboratory has already been successful in determining
DNA sequences unique to D. geminata, and the method is promising for monitoring efforts (Cary
et al. 2006). Following this work, the expanding distribution of D. geminata has prompted a
genetic survey to determine: 1) How genetically related are populations of D. geminata around
the world? 2) Are there one, or more, "source" populations that are able to spread to new sites? 3)
Has there been a genetic change in one or more populations that have led to invasive behavior? In
spring of 2006, Cary initiated a broad request to the scientific and management community to
contribute samples of D. geminata for a global population study. Samples have been contributed
from the broadest distribution possible, including but not limited to, representative samples from
Asia, Europe, and North America.

In determining if there has been a genetically based physiological change linked to a nuisance
strain, it is important to consider different types of change. Physiological changes may include
general physiological changes, including such processes as photosynthetic capacity and
ecological tolerances. Such changes might allow expansion into new habitats. In addition, there
may be specific changes in mode of production of stalk, that is, alterations in the synthesis of
extra polymeric substances (EPS). Have the signal and regulatory genes in D. geminata become


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Research and management response to D. geminata Page 19

activated in response to environmental cues to result in excessive stalk production? It is critical to
determine if enzymes (such as glycan synthase and glycosyl transferase) are responsible for the
excessive stalk production. Other diatom species produce stalks and may also have the potential
to become nuisance species if EPS production becomes "turned 011".

Range expansion

The mechanisms for D. geminata to expand its
range to new watersheds are not well
understood. Early suggestions that increases in
UV-B radiation was tied to the expansion were
not supported (Sherbot & Bothwell 1993,
Wellnitz et al. 1996, Rader & Belish 1997).
Recent work illustrates the capacity of D.
geminata to survive outside of the stream
environment as well as potential vectors in its
spread. Cells are able to survive and remain
viable in cool, damp, dark conditions for at
least 40 days (Kilroy 2005). Fishing
equipment, boot tops, neoprene waders, and
felt-soles in particular, all provide a site where
cells remain viable, at least dunng short term
studies (Kilroy et al. 2006). At the same time,
prime destinations for fishing are becoming
more popular with anglers. Rather than
frequent a favorite local fishing site, it is now
common that anglers travel to multiple, or
distant destinations for fishing vacations.
Moreover, they may be fishing in a river less
than twenty four hours after leaving their local

Figure 17. An increasing number of anglers from North America are visiting other continents to fish, as illustrated by
this tourist in Rio Malleo, Argentina. Ecological models predict that rivers in South America and Australia contain
suitable habitat forD. geminata. (Image by Matt Wilhelm, Federation of Ely Fishers).

For aquatic organisms, the relationship between the spread of invasive species to recreation is
well established (e.g., Eurasian water milfoil (Myriophylhim spicatum L.) and zebra mussels
(Dreissenapolymorpha)) (e.g., Madsen et al. 1988, Strayer et al. 1996, Vitousek et al. 1997,
Schneider et al. 1998, Johnson et al. 2001). Gear and equipment used in aquatic recreation is
being tested for its role in spreading D. geminata, but it is possible that humans transport D.

rivers in North America, and unknowingly
spreading D. geminata.

Figure 16. D. geminata is able to survive on boot tops,
neoprene waders, and felt-soles and may be spread to
distant sites (Image by Sarah Spaulding, US Geological
Survey).


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Research and management response to D. geminata Page 20

geminata in other ways (e.g.. boats including jet skis, water transport for rural fire fighting,
irrigation, water diversions, waterfowl hunting, and float airplanes). Determining the likely risk of
such vectors may be valuable for targeting control programs and public messages about
decontamination.

Economic impact

While D. geminata is not considered
invasive in the United States, the diatom's
nuisance blooms has economic impacts. The
human population of western United States
is closely dependent on a system of canals to
transport water for hydropower generation,
agriculture, and human consumption.

Nuisance algae, including D. geminata,
regularly thrive on the stable substrate and
flow regime of canal systems (Pryfogle et al.

1997). In some canal systems, managers
implement regular removals by scraping I),
geminata growths from the concrete
surfaces of canals (Fig. 18).

Didymosphenia geminata is often reported by recreationalists to land managers as being unsightly
(see Appendix D). The stalks are frequently mistaken for raw sewage, leading homeowners and
recreationalists to complain to local water treatment plants. Many communities rely on tourism
dollars that are generated by outdoor recreation. Natural resource opportunities represent
important economic value, yet they may be vulnerable to damage by the spread of nuisance
species. In the United States, the cost to control and eradicate nuisance and invasive species is
estimated at $120 billion annually, with $1 billion from the impacts of invasive zebra mussels
alone (Pimentel et al. 2005).

Upon the appearance of D. geminata in New Zealand in October 2004, Biosecurity New Zealand
initiated a national incursion response based on the potential losses to the national economy. The
presence of D. geminata threatens the opportunities for tourists to experience clear, unimpacted
rivers. Commercial eel fisheries, water supplies, tourism, and biodiversity values are projected to
be impacted and economic losses are estimated at between NZ $57 and 285 million over a period
of eight years (Branson 2006).

Control techniques

Biosecurity New Zealand is currently pursuing a series of experimental trials to test biocides for
potential control of D. geminata within streams and rivers in New Zealand (Jellyman et al. 2006).
In order to test the efficacy of various biocides, D. geminata was grown on artificial substrates
and placed in experimental stream channels. Several biocides were tested on D. geminata. The
mats were exposed to each biocide for a period of one hour and the viability of algal cells
determined at various time periods, up to 28 days after treatment. Mortality of fish in the
experimental stream channels was also assessed. Of the five biocides tested, chelated copper had
the greatest negative effect on D. geminata for all contact times. In the next stages, the tolerance
limits of fish to chelated copper will be established. Although copper compounds have a long
history of use as algaecides the United States, in lakes, reservoirs, and to a lesser extent, flowing
waters, they have not been evaluated for control of D. geminata outside of New Zealand.

Figure 18. Stalks of A geminata clog a grate in a
water supply canal in California (Image by Peter
Pryfogle, Idaho National Laboratory).


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Research and management response to D. geminata Page 21

Reduce the Spread

Plants, animals and microscopic organisms, including D. geminata, may adhere to waders, boots,
boats, float tubes, and angling gear. Cleaning gear before traveling between bodies of water,
whether between nearby streams or for international destinations, is crucial. Decontamination of
gear is the only way to prevent the spread and subsequent introduction of D. geminata into new
watersheds. While decontamination will not destroy all invasive species, cleaning procedures
minimize the possibility of spread. These simple treatments effectively destroy 11 geminata algal
cells (Kilroy 2005):

Before leaving a river's edge, look for clumps of algae and sediment, and
remove them Leave them at the site

Soak and scrub all gear for at least one minute in a 2% (by vol ume) solution
of household bieach, or a 5% (by vol ume) solution of salt, or dishwashing
detergent. Note that all surfaces must be contacted by the cleaning solution
Water-absorbanl equipment (I ifejackets, waders) sho Lid be soaked to insure
they do not remain a risk.

If cleaning is not practical, after the item is dry to the touch, leave it to dry for
at least 48 hours before using in another freshwater system

Figure 19. Recommended methods to prevent spread oiD. geminata (Graphic from EPA .information sheet).

An aggressive education and outreach program is required to change water resource user behavior
in order to minimize spread of D. geminata on a global scale. A public awareness campaign,
directed at freshwater anglers, boaters, professional guides, and other recreationalists must be
integrated with existing invasive species programs. Freshwater resource users, including
ecologists, water managers, fisheries biologists, and other scientists, need to be aware of the
threat and should practice decontamination procedures to prevent the spread. Furthermore,
members of the United States Aquatic Nuisance Species (ANS) Task Force must be informed of
the distribution and impact of D. geminata, and include this organism within the scope of
nuisance and invasive species within the United States.

Summary

Didymosphenia geminata now has a broad distribution in North America, a condition that appears
to have developed in the past ten to twenty years. Although the diatom is more common in the
western United States, it is also forming large growths in rivers in the eastern United States and
Canada. This diatom was known to produce large masses since the earliest historical records, but
now the blooms are over a greater area m the Northern Hemisphere and spreading across rivers in
the Southern Hemisphere While D. geminata was formerly considered to have narrow ecological
tolerances, it is now present in streams exhibiting a wide range of chemical characteristics. It is
capable of growing throughout most of the year in streams with low to high N03 concentrations
(< 1 mg/1 - > 8 mg/1), low to high temperatures (4-27 °C), and within a broad range of light
exposure. The diatom forms an unknown number of nuisance blooms in North America, covering
benthic surfaces for greater stream reaches than 1 to 2 km. The diatom is invasive in New
Zealand, and is rapidly expanding to new watersheds, despite aggressive control measures.

Didymosphenia geminata causes us to question our fundamental understanding of streams and
rivers. First, D. geminata presents a biological paradox; how is excessive biomass produced in
low nutrient streams and rivers, over short periods of time? Second, D. geminata produces a
mucopolysaccaride stalk that appears to be resistant to biodegradation by bacteria and fungi.

What is the unique composition and structure of the stalk, and how does the stalk itself play a role

DON'T SPREAD DIDYMO check:
DON'T SPREAD DIDYMO

DON'T SPREAD DIDYMOCLEAN:
DON'T SPREAD DIDYMO

DON'T SPREAD DIDYMOH^B

DRY:


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Research and management response to I). geminata Page 22

in the success of this organism? Third, D. geminata has direct and indirect impacts across aquatic
trophic levels. What is the long-term significance of stalks that are resistant to decomposition and
trap fine sediment past the life span of the organism? Fourth, there are suggestions that
macroinvertebrates and fish respond to nuisance levels of D. geminata with community and
population level shifts in composition, abundance, and size class. What are the trophic impacts of
D. geminata? Finally, is there a genetically based physiological change in this organism that is
linked to a nuisance strain? Molecular markers present the opportunity to trace the genetic
relationships of nuisance outbreaks and those records can be compared with models of predicted
global distribution.

Scientists, conservationists and natural resources managers are concerned about nuisance blooms
of D. geminata and change in behavior of this organism or appearance of a nuisance strain. As an
outcome of the International Didymosphenia Symposium in Bozeman, Montana, two goals are
clear:

1)	Develop an outreach effort to inform and involve the public and government agencies

2)	Develop an approach to research that will allow us to address the behavior and impacts of

this organism.

This document and the following recommendations are intended to accomplish those goals.

Recommendations

•	An aggressive education and outreach program is required to change water resource
user behavior in order to minimize spread of D. geminata on a global scale.

o A public awareness campaign, directed at freshwater anglers, boaters,

professional guides, and other recreationalists must be integrated with existing
invasive species programs,
o Freshwater resource users, including ecologists, water managers, fisheries

biologists, and other scientists, need to be aware of the threat and should practice
decontamination procedures to prevent the spread,
o Members of the United States Aquatic Nuisance Species (ANS) Task Force must
be informed of the distribution and impact of D. geminata, and include this
organism within the scope of nuisance and invasive species within the United
States.

o Rivers in the southern hemisphere are particularly at risk to new introduction and
invasion. Appropriate agency personnel in Australia, Argentina, Chile and Peru
must be notified and made aware of the potential ecological damage and urgency
of implementing decontamination procedures.

•	Determine if there has been a genetically based physiological change in this organism
that is linked to a nuisance strain. Physiological changes may be:

o General physiological changes, including such processes as photosynthetic

capacity and ecological tolerances,
o Specific changes in mode of production of stalk, that is, alterations in the
synthesis of extra polymeric substances (EPS).

•	Trace the relationships of nuisance outbreaks and those records can be compared
with models of predicted global distribution using molecular markers.

•	Determine the degree to which the spread of D. geminata is aided by specific human
vectors, such as felt-soled waders, or other plausible mechanisms.

•	Track the geographic distribution of D. geminata on a global scale using effective
and proper documentation of sites and voucher samples.


-------
•	Determine the ecological conditions under which excessive biomass is produced in
low nutrient streams and rivers, over short periods of time. Develop strategies to
mitigate existing blooms.

•	Determine the unique composition, structure, and cellular processes that produce the
D. geminata stalk, which is responsible for its negative ecosystem impacts.

•	Determine it perturbations in signal, regulatory, and/or synthetic pathways of stalk
production by cymbelloid diatoms has resulted in increased production in D.
geminata.

•	Evaluate the apparent resistance of the stalk to degradation by bacteria and fungi, and
determine ecosystem effects of stalk material.

•	Investigate the contribution that D. geminata makes to nutrition of
macroinvertebrates. Are macroinvertebrates able to access the cells from within the
mass of stalks?

•	Resolve the extent to which macroinvertebrate grazing can reduce D. geminata
abundance.

•	Determine the direct and indirect impacts of D. geminata and its stalks to aquatic
macroinvertebrates and fish. Resolve the impacts of D. geminata at both high and
low densities and whether there are threshold levels of nuisance growths. Testing the
following hypotheses will clarify the potential impacts:

o The impact of D. geminata on aquatic macroinvertebrates is directly related to

temporal and spatial extent of nuisance blooms,
o D. geminata masses alter the taxonomic composition and size of benthic

macroinvertebrates present in the drift,
o The presence of D. geminata alters the energetics of fish through altering the

macroinvertebrates present in drift,
o The reduction in food energy reduces the growth rate of trout, and favors small
individuals over large individuals.


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Acknowledgements

This work could not been completed without the generous contributions of the Federation
of Fly Fishers, US EPA, and many individuals. The International Didymosphenia
Symposium was supported by the Trout and Salmon Foundation, Black Hills Fly Fishers,
and the Overmountain Chapter of Trout Unlimited. Thanks to Barry Biggs, National
Institute of Water and Atmospheric Research, New Zealand; Dave Beeson, ENVIRON
International Corp; Max Bothwell, Environment Canada; Craig Cary, University of
Waikato; Michael Gretz, Michigan Technological University; Karl Hermann, US EPA;
Ingi Jonsson, Iceland Institute of Freshwater Fisheries; Martyn Kelly, Bowburn
Consultancy, UK; Cathy Kilroy, National Institute of Water and Atmospheric Research,
New Zealand; Diane McKnight, University of Colorado; Sheila Murphy, US Geological
Survey; Kristina McNyset, US EPA; Yang Don Pan, Portland State University; Peter
Pryfogle, Idaho National Laboratory; Travis Schmidt, Colorado State University; Erica
Shelby, Arkansas Dept. of Environmental Quality; Jan Stevenson, Michigan State
University; Christina Vieglais, Biosecurity New Zealand; Rich Wanty, US Geological
Survey and Robert Wiltshire, Federation of FlyFishers.


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Appendix A: Additional Resources

Available resources for more information about Didymosphenia geminata and aquatic invasive
species.

Internet resources

Biosecurity New Zealand
www.biosecurity.govt.nz/didymo

United States Environmental Protection Agency
www.epa.gov/Region8/water/monitoring/didymosphenia.html

Federation of Fly Fishers

www. fedflyfishers.org/conInvasive Specie s .php

Stop Aquatic Hitchhikers
www.protectyourwaters.net/

Global Invasive Species Database
www.issg.org/database/species

State of Arkansas Department of Environmental Quality
www. adeq. state .ar .us/water/didymo .htm

New Zealand Game and Fish - Video clip
www. southlandfishgame .co .nz/didymo .htm

Symposium abstracts

Abstracts of presentations at the International Symposium on Didymosphenia are available. The
symposium was co-sponsored by the Federation of Fly Fishers and U.S. EPA Region 8, held in
association with the Western Division American Fisheries Society Annual Meeting May 15-16,
2006, Bozeman, Montana, USA.
http://www.epa.g0v/region8/water/events.html#agenda

Report occurrences

Report suspected growths of Didymosphenia by collecting a small sample (put a pinch of the
material in a vial with ethanol or in a folded business card). Label samples with the date, latitude,
longitude (provide detailed accurate site information). Send reports and samples to:

Dr. Sarah Spaulding
US Geological Survey
999 18th St., Suite 300
Denver, Colorado 80202 USA
Email: sarah.spaulding@usgs.gov
Tel: 303-312-6212


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Appendix B: Scientific meetings

Presentations at scientific meetings are a vital form for communication of scientific findings.
Issues stemming from D. geminata have stimulated a rapid and broad scope of research interests.
Scientists have presented, or are scheduled to present, talks or posters on D. geminata at the
following national and international scientific conferences:

CONFERENCE

DATE

LOCATION

LINK

Didymosphenia Symposium,

15-16 May 2006

Bozeman,

htte>://www.era.eov/reeion8/water/

American Fisheries Society



Montana, US

events.html

International Conference

15-18 May 2006

Key Biscayne,

htto://www.icais.ore/

Aquatic on Invasive Species



Florida, US



North American

4-9 June 2006

Anchorage, Alaska

htto://www.benthos.ore/Meetine/

Benthological Society



US



Phycological Society of

7-12 July 2006

Juneau, Alaska US

lUtD://\vww.Dsaalaac.ora/oDs/Dsa20

America





06.shtm

Joint Conference of the NZ

28 Aug -1 Sep

Wellington, New

www.vuw.ac.nz/ecolosv06

Ecological Society

2006

Zealand



International Diatom

28 Aug - 3 Sep

Irkutsk,

htto://lin.irk.ru/ids2006/

Symposium

2006

Russia



International Conference on

4- 8 Sep 2006

Copenhagen,

htto://www .bi.ku.dk/hab/

Harmful Algae



Denmark



NZ Freshwater Sciences

26-30 Nov 2006

Rotorua, New

htto://limsoc.rsnz.ore/

Conference



Zealand



American Society of

4-9 Feb 2007

Santa Fe, New

htto://www.aslo.ore/meetines.html

Limnology and



Mexico, US



Oceanography







Society for International

12- 18 Aug 2007

Montreal, Canada

htto://www.sil2007.ore/

Limnology








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Appendix C: Glossary

acid neutralizing capacity (ANC): A water chemistry measure that gives an indication of the
ability of a water sample to counter the effects of acid without changing its pH. Water low in
ANC may easily become acidic, while waters high in ANC are much more resilient. ANC is a
measure similar to alkalinity, which is a measure of the buffering capacity of a water sample.

apical pore field: A structure that is part of the silica cell wall of diatoms. The apical porefield is
an area of very fine pores, through which the mucilaginous stalk is secreted. Didymosphenia
geminata has a single apical porefield on one end of each valve.

ash free dry mass (AFDM): A measure which indicates the amount of organic material present in
a sample.

benthic or benthos: Refers to the bottom surface of a stream, river, or lake. The aquatic organisms
that live in, on, or near the bottom surface are termed benthic organisms and they inhabit the
benthos. Benthic organisms may include macroinvertebrates, algae, bacteria, fungi, clams,
worms, and anything else that inhabits the bottom.

chlorophyll a: Chlorophyll is the primary pigment used by plants to obtain energy from the sun
through photosynthesis. Chlorophyll a is a specific form of the chlorophyll molecule found in
photosynthetic algae. The amount of chlorophyll a in a stream gives an indication of the amount
of algal biomass present. High amounts of algal biomass are usually considered undesirable and
indicative of increased nutrient loads.

chrysolaminarin (B1.3 linked glucan): A molecule produced by some groups of algae including
the diatoms. The material is composed of modified glucose, functions as a food reserve, and is
stored within the cell.

cymbelloid: Referring to a group of freshwater diatoms within the Family Cymbellaceae.
Cymbelloid symmetry is typically asymmetrical to both primary axes (the cells are crescent
moons in shape). Although D. geminata is a member of this group (Kociolek & Stoermer 1993),
it does not share the characteristic symmetry.

EDTA or ethylenediaminetetraacetic acid: A specific molecule that binds strongly to ions in a
solution. In the example given here, EDTA is used to bind and separate fractions of the diatom
stalk.

eutrophic/Waters that are high in nutrients, specifically phosphorus and nitrogen, are considered
eutrophic. High concentrations of phosphorus and nitrogen often lead to correspondingly high
algal productivity and biomass.

extracellular: Material that is located outside the boundaries of the cell wall. In the example of D.
geminata, the stalk is produced within the cell but is then excreted outside the cell wall.

gomphonemoid: Referring to group of freshwater diatoms within the Family Gomphonemaceae.
Gomphonemoid symmetry is typically symmetrical to the apical axis, and asymmetrical to the
transverse axis (the cells are club shaped). Although D. geminata is often included in this group


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because it has gomphonemoid symmetry, Kociolek & Stoermer (1993) demonstrated it is a
member of the cymbelloid lineage.

invasive species: Any species, including its seeds, eggs, spores, or other biological material
capable of propagating that species, that is not native to that ecosystem; and whose introduction
does or is likely to cause economic or environmental harm or harm to human health.

molecular markers: Specific sequences of genetic material (DNA) that are used to characterize or
differentiate organisms.

mucopolysaccaride: A complex chain of molecules primarily composed of sugar molecules
linked together to form a chain. The diatom stalk is composed of mucopolysaccarides.

nuisance bloom: The term "bloom" is traditionally applied to planktonic algae that form growths
in lakes or oceans. It is not a "bloom" in the sense of flowering plants. Here, the term "nuisance
bloom" is applied to the condition that D. geminata creates in streams because the growths
threaten the diversity of other species, aquatic ecosystem function, or economic activities
dependent on flowing waters.

oligotrophic: Waters that are very low in nutrients, specifically phosphorus and nitrogen, are
considered oligotrophic. Such low nutrient waters are usually low in algal productivity and
biomass.

periphyton: Although the strict definition of periphyton is "growing on or around plants", the
term is used to apply to photosynthetic organisms (mostly algae) growing on surfaces in aquatic
systems. The algae in periphyton is an important source of food for organisms of higher trophic
levels (e.g., macroinvertebrates, fish).

plankton: Organisms that have little or no ability to control their position within a body of water,
that is, they are suspended in the water column. Plankton may be photosynthetic and plant-like
(phytoplankton), heterotrophic and animal-like (zooplankton), or composed of bacteria
(bacterioplankton).

raphe: A structure in the silica cell wall of some diatoms. Diatoms that possess this slit-like
structure are able to move on the surface of substrates. Because these cells can move, they have
some ability to select preferred habitats for growth. Didymosphenia cells possess a raphe which is
functional before cells anchor to a substrate via a stalk.

valve: The siliceous part of the diatom cell wall is composed of two parts, termed valves.
Together, the two valves are called a frustule. Diatom valves are often highly ornamented and
diatom taxonomy is primarily based on the morphology of these structures.

visual biovolume index: A measure developed in New Zealand to assess the impact of D.
geminata cells and stalks to a stream ecosystem. The index is a measure of the percent cover of
algal mat in a stream transect multiplied by the thickness of the algal mat.


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Appendix D: Media coverage

Magazines
Flyfisher, Fall 2006

Dealing with didymo

FlyRod and Reel, April 2006

Short Casts: getting to know didymo

South Dakota Conservation Digest, March/April 2006

Didymo and the Rapid Creek brown trout

Biosecurity, February 2006

Personal responsibility key to stopping didymo spread

High Country Angler, Winter 2006

"Didymo" What is it, and should we be worried?

Print articles

Bozeman Daily Chronicle, May 16, 2006

Algae outbreak threatens rivers around world

Bozeman Daily Chronicle, May 14, 2006

Scientists to gather and discuss slimy algae

Colorado Daily, November 6, 2005

"Rock snot" spreading: pesky algae could threaten waterway ecosystems across country

Denver Post, November 1, 2005

Slime covers streams

Rapid City Journal, April 14, 2005

Algae invader: survey tracks spread of "thug"

Online articles

Montana's News Station, May 16, 2005

Slimy algae draws scientists to Bozeman
www.kbzk.com

Vail Daily, May 18 2006.

Didymo along the Gore Creek in Vail
www. vaildaily. com

Billings Gazette, May 18, 2006

Slimy alga threatens state rivers
www.billingsgazette.net


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