DESIGN AND CONSTRUCTION OF A
SALTWATER ENVIRONMENT SIMULATOR
FEDERAL WATER
QUALITY
ADMINISTRATION
NORTHWEST REGION
PACIFIC NORTHWEST
WATER LABORATORY
CORVALLIS, OREGON
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DESIGN AND CONSTRUCTION OF A
SALTWATER ENVIRONMENT SIMULATOR
by
Waldemar A. DeBen
Working Paper Number 71
United States Department of the Interior
Federal Water Pollution Control Administration, Northwest Region
Pacific Northwest Water Laboratory
200 Southwest Thirty-fifth Street
Con/all is, Oregon 97330
April 1970
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FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
NORTHWEST REGION, PORTLAND, OREGON
James L. Agee, Regional Director
PACIFIC NORTHWEST WATER LABORATORY
CORVALLIS, OREGON
A. F. Bartsch, Director
NATIONAL THERMAL NATIONAL EUTROPHICATION
POLLUTION RESEARCH RESEARCH
Frank H. Rainwater A. F. Bartsch
NATIONAL COASTAL WASTE TREATMENT RESEARCH
POLLUTION RESEARCH AND TECHNOLOGY: Pulp &
D. J. Baumgartner Paper; Food Processing;
Wood Products & Logging;
BIOLOGICAL EFFECTS Special Studies
Gerald R. Bouck James R. Boydston
MANPOWER AND TRAINING CONSOLIDATED LABORATORY
Lyman J. Nielson SERVICES
Daniel F. Krawczyk
NATIONAL COASTAL POLLUTION
RESEARCH PROGRAM
D. J. Baumgartner, Chief
R. J. Call away
M. H. Feldman
G. R. Ditsworth
W. A. DeBen
L. C. Bentsen
D. S. Trent
D. L. Cutchin
D. R. Hancock
E. M. Gruchalla
L. G. Hermes
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DEPARTMENT OF THE INTERIOR
In its assigned function as the Nation's
principal natural resource agency, the
Department of the Interior bears a special
obligation to assure that our expendable
resources are conserved, that renewable
resources are managed to produce optimum
yields, and that all resources contribute
their full measure to the progress, pros-
perity, and security of America, now and
in the future.
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CONTENTS
Chapter Page
I. INTRODUCTION 1
II. SIMULATOR 3
Description 3
Salinity 8
Temperature 18
Oxygen 20
Water Filtration System 21
Salt Water 21
Fresh Water 25
Additional Equipment Used 25
III. CONCLUSION AND SUMMARY 27
ACKNOWLEDGMENTS 29
REFERENCES 30
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LIST OF FIGURES
Figure Page
1 Side View of Water Storage Tank, Tank Tower,
and Test Table 4
2 Top View of Water Storage Tank, Tank Tower,
and Test Table 5
Key to Numbers for Figures 1 and 2 6
3 Cut-away View of Basic Salinity Sensing Unit .... 10
Key to Numbers for Figure 3 11
4 Electrical Diagram of Salinity Sensor Controlling
Water Storage 13
Key to Numbers for Figure 4 ' . 14
5 Electrical Plan for Adjustment Tank Salinity
Sensor and Monitoring Unit 16
Key to Numbers for Figure 5 17
6 Cut-away View of Saltwater Filter Body 22
Key to Numbers for Figure 6 23
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INTRODUCTION
Field studies complemented by laboratory work are essential
in evaluating conditions which may be detrimental to a biotic
community. Water quality criteria must take into account long-
term, sublethal exposure effects on test organisms.
Laboratory efforts to provide information on factors that
influence organism abundance and state of health require simulation
and control of natural environmental parameters. Most systems in
current use involve static water bioassays or recirculating sys-
tems. Burke and Ferguson (1968) state that:
...objectionable features of static tests include a
decline in concentration of toxicants during the
exposure period by uptake by the experimental organ-
isms, its adsorption onto the container or other
surfaces, and its chemical alteration Furthermore,
accumulation of waste products, reduction of dis-
solved oxygen supply, and growth of microbial popula-
tions may produce an undesirable test environment.
Poole (1966), while rearing Cancer magister zoeae under static
water conditions, encountered heavy mortality due to microbes.
Burdick (1967) believed that continuous-flow assays are ideal for
either long or short-term tests and that this type of system may
be used to establish the test animal's physiological limits of
resistance.
Described in this report is an experimental, continuous-flow
bioassay apparatus designed to utilize and stabilize saltwater
derived from an estuarine source. The prototype was constructed
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2
to provide a single-test supply of up to eight liters of test
water per minute at four levels of selected temperature and a
near-constant concentration of any selected salinity or dissolved
oxygen. Provision for the introduction of measured quantities of
specific materials for test completed the basic system.
This apparatus, called the "Saltwater Environment Simulator"
(or "Simulator"), was intended for use in evaluating the effects of
pollutants and natural environmental changes on marine and estuarine
animals. It was constructed by personnel of the National Coastal
Pollution Research Program of the Federal Water Pollution Control
Administration located in the Marine Science Center at Newport,
Oregon.
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SIMULATOR
Description
The Saltwater Environment Simulator consists of three basic
units: (1) a water storage tank to ensure the availability of a
selected high salinity water during operation, plus a filter to
eliminate suspended material from entering the rest of the system;
(2) a tower to support a salt-freshwater mixing tank, a head tank,
and aeration, degassing, and heat exchange equipment; and (3) a
table for heating chambers, flow meters, animal holding tanks,
and temperature monitoring thermocouples. A side view diagram
of the tank, tower, and table is shown in Figure 1 and a top view
diagram in Figure 2.
The saltwater supply for the Marine Science Center is pumped
from an intake located about two feet off the bottom of Yaquina
Bay at depths of approximately 20 to 30 feet, depending on tidal
stage, and distributed throughout the laboratory in polyvinyl
chloride (PVC) pipe. High salinity water enters the 600-gallon
epoxy-painted metal storage tank from the laboratory line via a
motor valve. This quantity of water is sufficient to sustain the
system over any ordinary low salinity period during a single tidal
cycle. Suspended material settling in the tank is removed periodic-
ally by using a small centrifugal pump attached to a piece of
suction hose and pipe.
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Rgl. Side view of water storage tank, tank tower, and test table.
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2. Top view of water storage tanK, tank tower, and test table.
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KEY TO NUMBERS FOR FIGURES 1 AND 2
Number Item(s)
1 Saltwater storage tank
2 Float switch panel
3 Flex-liner water pump
4 Saltwater filter
5 Freshwater filter
6 Freshwater line
7 Electric valve actuator
8 Saltwater valve
9 Stirring motor
10 Salinity adjustment tank
11 Salinity sensor,
12 Wastewater bucket
13 Head tank
14 Saltwater return line
15 Gas extraction tube
16 Immersion cooling unit
17 Antifreeze-water bath
18 Centrifugal pumps
19 5-gallon plastic containers
20 Water manifold
21 Line to manifold
22 Heating chamber
23 Heater and thermoregulator
24 Flow meter
25 Animal test tank
26 Thermocouple container
27 Plastic drain pipe
28 Test table
29 Oxygen sampling tube
30 Laboratory saltwater line
31 Wastewater trough
32 Constant head bucket
33 Timing motor
34 Circuit breaker box and electrical panel
35 Temperature strip chart recorder
36 Pressure relief valve
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7
Stored seawater is forced through a filter for removal of the
remaining suspended matter and to the salinity adjustment tank
with a seal-less, neoprene flex-liner pump (5 gpm rating). A
safety float switch stops the pump when water level drops within
a few inches above the storage tank water outlet. Salt water
enters the salinity mixing tank at the rate of one gallon per
minute. PVC ball valves and a valve actuator control the rate
of saltwater flow and that of the fresh water used for dilution
and introduced through an auxiliary line. Both are discharged
through a common line near the bottom of the tank. Excess water
is returned to storage via an overflow bypass line.
The mixing tank has a 29-gallon capacity and is of poly-
ethylene construction. Two variable-speed motor stirrers with
three-bladed polyethylene stirring rods attached accomplish mixing.
Water temperature is held nearly constant in the tank with a mercury
thermoregulator-glass jacketed immersion heater combination. Two
discharge pipes are located at the brim of the tank - one to trans-
port water to a salinity sensor and to a 24-gallon head tank; the
other to serve"as the overflow line for returning excess diluted
water to the storage tank.
Salinity-adjusted water passes by gravity flow from the head
tank into the top of a glass oxygen "scrubbing" tube through a
distribution pipe at the bottom. At this point the flow is divided.
One portion is pumped through a stainless steel heat exchanger for
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cooling, and the other is pumped to heating chambers. Water to
be heated and the cooled water are directed into identical heating
chambers through separate manifolds at the rear of the test table.
Hand-adjusted PVC valves are used to regulate final flow rates
through the chambers and to the animal test tanks. Temperature -
adjusted water leaving the chambers passes through double-ball
flow meters to facilitate flow regulation. A flow rate of
500 ml/min/chamber usually was used during "checkout" procedures.
Maximum capacity is 1 L/min/chamber.
Water leaving the test chambers flows into eight-ounce poly-
ethylene jars, each of which contains a thermocouple for the
purpose of obtaining a continuous record of experimental tempera-
tures. All discharge water is piped to a drain trough in the
floor.
Salinity
Accurate control of salinity is one of the most important
functions in the development of a flowing seawater system.
Laboratory animals subjected to fluctuating salinities undergo
ionic, osmoregulatory, or other physiological changes that can
influence experimental results. Fluctuating tidal levels and
freshwater inflows complicate the control problem.
A salinity sensing device composed of a hydrometer, photocell-
relay, and electric valve actuator was fabricated to continuously
monitor the incoming estuarine water and to regulate the flow of
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9
a desired salinity into the storage tank. The device is designed
to accept all water of selected or higher salinities and to reject
or close the intake valve to water of lesser specific gravity.
A float switch controls the opening and closing of the valve when
a continuous supply of high-salinity water is available.
A cut-away view of the salinity sensing unit, less hydrometer,
is shown in Figure 3. Water coming from the seawater system enters
near the base of the sensor through PVC pipe. The body and tubing
arrangement is fabricated from PVC pipe and plastic hose. Two
openings (windows) are located in the upper portion of the unit
and are enclosed in a movable machined plastic collar which func-
tions as a water spillway. Mounted above the "windows" in two
short pieces of pipe is a grid-type cadmium sulfide photocell-
relay and a 2.5 volt flashlight bulb. A small volume of incoming
seawater is introduced near the base of the sensing unit and allowed
to circulate around the hydrometer to the overflow spillway.
Construction methods and materials for the hydrometer are based
on the formula used by Thayer and Redmond (1969) to calculate
hydrometer stem diameter relative to body displacement. Discarded
standard seawater ampules are used to construct the hydrometer
body. A black plastic vane is attached to the stem of the hydrometer
to prevent light from energizing the photocell during periods of
salinity of lower than desired level.
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:ig3 Cut-away view of salinity sensor.
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KEY TO NUMBERS FOR FIGURE 3
Number Item(s)
1 Flashlight bulb
2 Photocell-relay unit
3 "Window"
4 Water spillway
5 Movable plastic collar
6 Cell body
7 Water entrance pipe
8 Cell base
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Five precalibrated hydrometers were made for salinities of
5, 10, 15, 20, and 25 o/oo. Seawater of greater specific gravity
than the control hydrometer displaces the hydrometer upward to
raise the vane out of the light path, thereby energizing the photo-
/
cell and valve actuator. A 25 o/oo hydrometer was used for test
operation of simulator systems. A diagram of the electrical sys-
tem which controls the entrance of high-salinity water into the
storage tank is shown in Figure 4.
Parallel platinum wire guides, mounted only in the mixing tank
sensor, are used to limit lateral movement of the hydrometer and
keep it in the light path at all times. The sensor fabricated for
the salinity adjustment tank is similar to the previously-mentioned
unit except that a Clairex CL-704* cadmium sulfide photocell with
a narrow (about 1/16-inch) light-sensitive band is used. By using
this type of photocell, slight changes in salinity will activate
or deactivate the motor valve circuit, therefore maintaining a
near-constant salinity.
Dilution and salinity control are accomplished with one of two
adjustment procedures. A test salinity in the 5 to 15 o/oo range
is rapidly obtained by manual adjustment of the freshwater ball valve
until a concentration 2 o/oo higher than desired is reached. The
valve actuator is allowed to automatically add the additional
fresh water required and to maintain the selected concentration.
Dilution to the 15 to 20 o/oo range is efficiently achieved without
* Mention of product or company name does not constitute endorsement
by the Federal Water Pollution Control Administration.
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10
Fjg. 4 Electrical circuit for control of sea water storage.
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KEY TO NUMBERS FOR FIGURE 4
Number Item(s)
1 Float switch
2 Sensor flashlight bulb
3 Grid-type photocell-relay
4 Switched line
5 2.5 volt filament transformer
6 Opening lead
7 Closing lead
8 Motor valve
9 Relay coil
10 Common line
11 Energized line
12 Neutral line
13 110-volt AC line
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manual assistance. A separate hydrometer, calibrated to the
desired salinity, is required for each experiment. Hydrometers
were constructed for each 5 o/oo interval.
The electrical diagram for the adjustment tank salinity sensor
and monitoring unit is shown in Figure 5. The salinity sensor acti-
vates the valve actuator to allow only small increments of fresh
water to enter the mixing tank at any one time. This system main-
tains limits within ±1 o/oo of the desired salinity as measured by
an RS5-3 electrodeless induction salinometer (Industrial Instruments)
mounted in the head tank. This salinity control is accomplished
by using the following components:
(1) Modified actuator valve. A small change in salinity (the
photocell responds to 0.3 o/oo difference), with subsequent move-
ment of the hydrometer, will cause activation or deactivation of
the photocell, which ultimately controls the direction of motor
valve rotation. Modification of rotation direction on the electric
valve actuator is accomplished by using two limit switches, one
which controls clockwise and the other counterclockwise rotation.
In the 90 degree rotation of the ball valve there are 12 stopping
points from open to closed positions. Both limit switches are under
the control of the photocell timer circuit.
(2) Photocell timer circuit. This circuit controls the quan-
tity arid duration of freshwater inflow into the salinity adjustment
tank. A one rpm (1/250 hp) timing motor drives a circular cam on
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II
12
13
Fig 5 Electrical circuit for salinity adjustment tank
sensor and monitor
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KEY TO NUMBERS FOR FIGURE 5
Number Item(s)
1 Motor valve
2 Limit switches
3 Roller switches
4 1 RPM timing motor
5 45-volt transformer
6 Full wave rectifier
7 50 mfd capacitor
8 10,000 ohm relay coil
9 Clairex photocell
10 Photocell activator light
11 Pilot light
12 250 ohm potentiometer
13 2.5 volt filament transformer
14 110=volt AC line
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which ride two roller microswitches. Current passing between the
rrricroswitches energizes the valve actuator, only if needed to
maintain desired salinity, for about 0.5 second every one-half
minute and either opens or closes the valve slightly, depending
upon the salinity.
All components except the valve actuator, photocell activator
light, and photocell are mounted on an electrical panel near the
base of the tower.
Temperature
Stable water temperatures within any laboratory system are a
necessity, since temperature variations alter the oxygen consumption
rate, growth, enzyme activity, toxicant uptake, and other metabolic
functions of aquatic animals. The temperature control capacity
of the simulator is designed to produce water temperatures similar
to those found in the environment, i.e., in areas of heated effluent
discharge or under the cool conditions of winter and upwelling.
The heat exchanger assembled for cooling consists of a 50-foot
length of 1/2-inch ID, 20 ga., #316 stainless steel tubing with
a surface area of approximately six square feet. It is formed
into a series of bends (resembling a trombone slide) and immersed
into a water-tight plywood box (21" x 17" x 25 1/4") covered with
a sheet of glass wool--aluminum foil insulation. This inner box,
which contains coolant, fits into a slightly-larger box to reduce
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heat transfer from the surrounding air. Thirty-five gallons of
a water-ethylene glycol mixture (4:1) is used in cooling.
Inserted through the top cover of the plywood cooling tank is
a 1/3 horsepower immersion cooling unit with a cold adjustment range
of from 2 to 20°C. This is adequate to lower the temperature of the
tank liquid to within a few degrees of the lower limit. The cool-
ant mixture is circulated at the rate of 4,500 gallons per hour
throughout the tank and over the compressor's stainless steel
cooling coils by a 1/12 horsepower circulator motor mounted in the
lower section of the cooling unit. Test water, cooled in circulating
through the 50-foot stainless steel coil, is transported to two of
the four heat adjustment chambers in insulated (glass wool-aluminum
foil) polyethylene tubing.
The four heating chambers, mounted in the rear of the testing
table, are constructed of four-inch PVC pipe 24 inches long, fitted
with threaded caps. The caps are drilled to accommodate rubber
stoppers which hold a one-half-inch bottom entrance pipe and a
similar size discharge pipe, mercury thermoregulator, and immersion
heater at the top. The chambers are covered with a layer of glass
wool-aluminum foil insulation to restrict the loss of heat. A
pre-set mercury thermoregulator (sensitivity to ±0.05°F temperature
change), heavy duty mercury plunger relay, and an interchangeable
750 or 1000 watt glass-jacketed immersion heater make up the
temperature control circuit for each chamber. Water temperatures
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remained within ±0.3°C of the desired setting for the duration of
checkout procedures as recorded on a twelve-channel strip chart
temperature recorder.
This recorder is sensitive to temperature ranges of from 0
to 60°C. The strip chart is graduated in 0.5°C divisions and hourly
intervals for easy reading. Each of the units' 12 thermocouples
is compacted ceramic insulated and sheathed in stainless steel.
Temperatures monitored, in addition to the animal test chamber
water, included air temperature over these test tanks, water in
the salinity adjustment and water cooling tanks, and water in a
tank used to acclimate animals to laboratory conditions.
Oxygen
Water is aerated to saturation or near-saturation with com-
pressed air in the head tank before it passes to the top of a glass
degassing column (3 1/2" x 4'). A constant head of water is main-
tained in the column by means of an overflow pipe inserted in a
machined PVC collar fitted at the top. As the water flows downward
the dissolved oxygen is displaced to the degree desired by a rising
shower of controlled nitrogen bubbles. Bottled nitrogen gas is
dispensed through a two-stage regulator attached by tubing to a
fritted dispersion disc placed in the bottom of the degassing
column. In tests using the diffuser stone alone, bubbles tended
to rise along one side of the column. A circular sieve plate was
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constructed from 1/4-inch plexiglass and several inches of glass
Raschig rings were placed on the sieve to eliminate this problem.
This dispersed the bubbles more or less evenly and removed the
dissolved oxygen more efficiently. Preliminary tests indicate
that dissolved oxygen levels can be maintained within limits of
±0.3 mg. dissolved oxygen per liter.
Water samples for dissolved oxygen determinations were taken
from a tube inserted in the line between the flowmeters and the
animal test chambers. The azide modification of the Winkler method
was used.
Mater Filtration System
Salt Water
Since different species of test animals have to be held for
different lengths of time during a test period, provisions were
made to ensure that adequate food could be supplied. Fish and
crustaceans were held in filtered flowing water with food intro-
duced into the test chambers. Non-filtered water could be routed
around the filter and pumped directly to the salinity adjustment
tank for filter feeding bivalve mollusks.
A cut-away view of the saltwater filter showing piping, valves,
and direction of saltwater flow (as indicated by arrows) is shown
in Figure 6. Filter body construction is based on a formula developed
by Neptune Microfloc, Inc., and filled with filter media consisting
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II
Rg. 6. Cut-away view of salt water filter body. Arrows
show path of salt water flow.
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KEY TO NUMBERS FOR FIGURE 6
Number Item(s)
1 Saltwater line from pump
2 Filter body
3 Media retainer
4 Support ring
5 Carborundum stone
6 Spacer ring
7 Plexiglass end piece
8 Support stand
9 Multiport ball valve
10 Wastewater discharge pipe
11 Freshwater line
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of fine and coarse garnet, ground carborundum, and anthracite coal.
Analysis of particle size using a Coulter Counter revealed no par-
ticles larger than 10 microns in water leaving the filter. The
filter can maintain water of this quality at a pumping rate of
5 gallons per minute.
Water enters through a multiport valve on the upper side of the
filter, passes down through the filtering media, and a porous car-
borundum stone, which retains the filter media, and out of the
filter through a multiport valve to the salinity adjustment tank.
During periods of freshwater runoff, with its accompanying large
load of suspended material, the filter media has to be cleaned about
every twelve hours. As the volume of entrapped material increases,
so does the amount of pressure exerted on the walls of the filter.
To prevent rupture of the filter body, the intake pipe is fitted
with a pressure relief valve, set to discharge water into a trough
when the pressure reaches 30 pounds per square inch.
In the cleaning or "backflushing" procedure, fresh water enters
the bottom of the filter body through a multiport valve, passes
through the carborundum stone and resuspends the sediment and
detritus trapped by the filter media. This dirty water then passes
through a multiport valve on the upper side of the filter body and
is discharged into a waste-water trough. The filter media is dis-
placed upward but not discharged, due to the retentive action of the
media retainer.
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Fresh Water
Fresh water used in dilution is piped by the Seal Rock Water
District to the Marine Science Center from various small streams.
Analysis of water for free chlorine showed none present. Upon
entering the building, the water passes through an activated char-
coal filter with a filtering rate of 35 gallons per minute. A
small charcoal filter is mounted in the waterline as a precautionary
measure.
Additional Equipment Used in the Simulator
Eight animal test chambers were constructed for initial simulator
trials. Each held approximately six gallons (40" x 6" x 9") and
was made from 3/16-inch black plexiglass. Water entered near the
bottom of one end and was discharged near the top of the other.
The bottom is sloped to form a shallow "vee" to facilitate collec-
tion of feces and uneaten food. This waste material is flushed out
by a drain in the bottom end of the tank. Black plexiglass was
chosen to reduce any adverse effect in the behavior or physiology of
test animals caused by external stimuli. Circulation of water
through the tank, at a rate of 500 ml per minute, was studied by
using neutral red dye. The result showed a well-mixed dye through-
out the chamber, indicating that an introduced toxicant would
probably follow this pattern. Temperature measurements within the
animal tank showed no gradients present.
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Test materials can be metered into the system at a point imme-
diately before entering the test tanks, A ten-vein metering pump
with a 0.12 to 5.25 ml per minute flow, depending on tubing size,
was used for this purpose. Mounted above the metering pump are
seven five-gallon plastic carboys, each connected to the pump by
flexible plastic tubing. The carboys can contain several types
and concentrations of test materials. The diluent water and test
material were found to be adequately mixed in either a small plexi-
glass chamber with a series of baffle plates or a small (250 ml)
filter flask.
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CONCLUSION AND SUMMARY
An experimental apparatus to control the environmental parameters
of salinity, temperature, and dissolved oxygen was designed and
constructed for the purpose of obtaining information on various
physiological processes in test animals and to complement field
studies carried out on estuarine fauna.
Salinity was controlled and adjusted by using a sensing unit
employing a photocell-hydrometer-motor valve actuator system which
maintained the salinity at ±1 o/oo of the desired test salinity.
Temperature regulation was accomplished by using a stainless
steel heat exchanger immersed in a cold antifreeze bath for cool-
ing, while water was heated by using glass-jacketed immersion heaters
working in conjunction with sensitive mercury thermoregulators.
Water temperatures were maintained within ±0.3°C of the desired
setting.
Oxygen levels were maintained by metering nitrogen gas through
a two-stage regulator to a diffuser stone, mounted in the base of
a large glass tube, which released an ascending shower of bubbles
and decreased the amount of dissolved oxygen in the water, which
entered at saturation or near-saturation levels at the top of the
tube. Oxygen levels of ±0.3 mg. per liter could be maintained in
the system.
Preliminary tests have shown that this apparatus will provide
controlled environmental conditions to better define some of the
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physiological requirements of test animals living under estuarine
conditions that can be related to ecological field studies. The
capability of inducing conditions of "stress," either by changing
one or more of the parameters or by introduction of a specific
material, can help to establish water quality standards in the
saltwater environment.
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ACKNOWLEDGMENTS
! wish to thank W. D. Clothier for his suggestions and manu-
script review, and W. P. Breese and his associates in the Depart-
ment of Fisheries and Wildlife, Oregon State University, for con-
ducting mussel larva bioassays to screen out any toxic materials
which might have been used in the construction of the simulator.
I also wish to thank 0. E. Thayer of the Marine Science Center
staff who gave useful advice on design, electrical instrumentation,
and construction problems.
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REFERENCES
Burciick, G. E. "Use of Bioassays in Determining Levels of Toxic
Wastes Harmful to Aquatic Organisms," A Symposium on Water
Quality Criteria to Protect Aquatic Life, American Fisheries
Society Special Publication No. 4, 1967. pp. 7-12.
Burke, W. D., and D. E. Ferguson. "A Simplified Flow-through
Apparatus for Maintaining Fixed Concentrations of Toxicants
in Water," Transactions^ of the American Fisheries Society,
Vol. 97, No. 4, 1968.pp. 498-501.
Poole, R. L. "A Description of Laboratory-reared Zoeae of
Cancer magister Dana, and Megalopae Taken Under Natural
Conditions (Decapoda, Brachyura)," Crustaceana, Vol. 11,
No. 1, 1966. pp. 83-97.
Thayer, 0. E., and R. G. Redmond. "Budget Salinity Recorder,"
Limnology and Oceanography. Vol. 14, No. 4, 1969. pp. 641-
643.
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