Technical Report Series
Number 85-6
WATER QUALITY OF TWO CLOSED
RECIRCULATING SOFT SHELL CRAB
SHEDDING FACILITIES
Keith W. Gates
Jackie G. EuDaly
Amanda H. Parker
Laura A. Pittman
Georgia Marine Science Center
University System of Georgia
Skidaway Island, Georgia
WATER QUALITY OF TWO CLOSED
RECIRCULATING SOFT SHELL CRAB
SHEDDING FACILITIES
Technical Report 85-6
by
Keith W. Gates, Jackie G. EuDaly,
Amanda H. Parker, and Laura A. Pittman
University of Georgia
Marine Extension Service
P. 0. Box Z
Brunswick, Georgia 31523
This Technical Report Series of the Georgia Marine Science Center
is issued by the Georgia Sea Grant College Program and the Marine
Extension Service of the University of Georgia on Skidaway Island
(P. 0. Box 13687, Savannah, GA 31416). It was established to
provide dissemination of technical information and progress
reports resulting from marine studies and investigations mainly by
staff and faculty of the University System of Georgia. In
addition, it is intended for the presentation of techniques and
methods, reduced data, and general information of interest to
industry, local, regional, and state government and the public.
Information contained in these reports is in the public domain.
If this publication is cited, it should be cited as an unpublished
manuscript. This work is a result of research sponsored by the
Gulf and South Atlantic Fisheries Development Foundation, Inc.,
The University of Georgia, and the NOAA Office of Sea Grant,
Department of Commerce under Grant #04-8M01-175 and Contract #A/G1. The U. S. Government is authorized to produce and distribute
reprints for governmental purposes notwithstanding any copyright
notation that may appear hereon.
ACKNOWLEDGMENTS
The authors wish to thank Mr . James Holland of Brunsw ick,
Georgia for h i s cooperat ion and assistance and for the use of his
two rec i rculating soft shell crab shedding systems. The technical
assistance of Mr. Tom Sh ierl ing, Ms. Lura Rel i han, and Ms. Caro l e
Greene was great l y apprec iated.
i i
TABLE OF CONTENTS
Acknowledgments
Abstract
v
List of Figures
vii
List of Tables
xi
Introduction
Methods
Results
3
Discussion
7
Conclusions
8
Figures
9
Tables
42
References
45
iii
iv
ABSTRACT
The water quality of two Georgia commercial recirculating
soft shell blue crab shedd i ng systems was monitored chemically and
microbiologically. A b iolog ical f i lter of crushed coral
ma i nta ined water qual i ty i n system one, whi l e an oyster-she ll
filt er and prote in skimmer combination supported system two
(O ster ling , 1984). The following parameters were determ ined for
each system stocked with crabs at h ig h and l ow dens iti es: total
crabs , total shed crabs, total dead c rabs, total added cr abs,
temperature, salinity, pH, carbon dioxide, MPN to ta l coliforms,
MPN E. coli, mar i ne agar plate counts, disso lved oxygen , percent
oxygen saturat ion, b iolog ical oxygen demand, ammon i um, ammon ia,
nitrate, nitrite, ca lcium, and alkalin i ty. Nitrate, nitr ite, and
ammon i um concentrat i ons remained below toxic limits for mo lting
blue crabs in both filter systems. A sign i f icant negat ive
correlat ion was estab li shed between nitrate concentrations and the
number of crabs shed in the protein-skimmer system. Dissolved
carbon dioxide leve ls corre l ated s i gn ificantl y with total numbe r
of crabs in the prote in-skimmer system. Sal inity had a
significant negat ive correlation (r ange 13 to 16 ppt ) with the
number of crabs shed in the prote i n-sk immer system. Ammon ium,
ammon ia, and nitrite l eve l s were genera lly greater in the proteinskimmer system than in the biological-filter system.
v
vi
LIST OF FIGURES
Figure
1•
Outlet pH, temperature, and sal i n i ty levels for the
biological filter stocked at high densities
10
2.
Inlet and outlet pH, temperature, and salinity levels
for the b iol og ical filter stocked at low dens iti es
11
3.
Outlet dissolved oxygen and BOD levels for the
b iological f il ter stocked at high densit ies
12
4.
Mean i n l et dissolved 0 2 , dissolved C0 2 , alkal i n i ty,
calcium, and BOD levels for the b io logical filter
stocked at low densities
13
s.
Mean outlet dissolved o2 , dissolved C0 2 , alkal i nity,
calcium, and BOD levels for the b iolog ic al filter
stocked at low dens i ties
14
6.
Mean out l et oxygen-saturation levels for the
b iolog ical filter stocked at high densities
15
l·
Mean i nlet and outlet oxygen-saturat ion levels
for the biological filter stocked at low densities
16
8.
Mean out let ammon i um, ammonia, n i trate, and n i tr i te
levels for the bio l ogical filter stocked at high
densit ies
17
9.
Mean inlet ammonium, ammon ia, nitrate, and nitrite
levels for the b io log ic al filter stocked at low
dens iti es
18
10.
Mean outlet ammon ium, ammonia, nitrate, and nitrite
leve ls for the b i o log ical filter stocked at low
dens iti es
19
11.
Mean outlet mar ine agar plate counts for the
b iolog ical filter stocked at high densities
20
12.
Mean inl et and out let mar ine agar plate counts for
the biological filter stocked at low dens iti es
21
13.
MPN total coliform and MPN E. coli outlet populat ions
for the b iol ogical filter stocked at high dens iti es
22
vii
Figure
14.
MPN total coliform and MPN E. coli inlet and outlet
populations for the biological~ter stocked low
densities
23
15.
Inlet and outlet pH, temperature, and salinity levels
for the protein skimmer stocked at high densities
24
16.
Inlet and outlet pH, temperature, and salinity levels
for the protein skimmer stocked at low densities
25
17.
Mean inlet dissolved o2 , disso lved CO~, alkalinity,
calcium, and BOO levels for the protein skimmer
stocked at high densities
26
18.
Mean outlet dissolved 0 2 , dissolved co 2 , a lkalinity,
calcium, and BOO levels for the protein ski mmer
stocked at high densities
27
19.
Mean inlet dissolved 0 2 , dissolved CO{, alkalinity,
calcium, and BOO levels for the protein skimmer
stocked at low densities
28
20.
Mean outlet dissolved 0 2 , dissolved C0 2 , alkalinity,
calcium, and BOO levels for the protein skimmer
stocked at low densities
29
21.
Mean inlet and outlet oxygen-saturation levels for
the protein skimmer stocked at high densities
30
22.
Mean inlet and outlet oxygen-saturation levels for
the protein skimmer stocked at low densities
31
23.
Mean inlet ammonium, ammonia, nitrate, and nitrite
leve ls for the protein skimmer stocked at high
densities
32
24.
Mean outlet ammonium, ammonia, nitrate, and nitrite
levels for the protein skimmer stocked at high
densities
33
25.
Mean inlet ammon ium, ammonia, nitrate, and nitrite
levels for the protein skimmer stocked at low
densities
34
26.
Mean outlet ammonium, ammonia, nitrate, and nitrite
levels for the protein skimmer stocked at low
densities
35
viii
Figure
27.
Mean inlet and outlet marine agar plate counts for
the protein skimmer stocked at high densities
36
28.
Mean inlet and outlet marine agar plate counts for
the protein skimmer stocked at low densities
37
29.
MPN total coliform and MPN E. coli inlet and outlet
populations for the protein skimmer stocked at high
densities
38
30.
MPN total coliform and MPN E. coli inlet and outlet
populations for the protein skimmer stocked at low
densities
39
31.
Total crabs, total crabs added, total crabs shed, and
total dead crabs for the protein skimmer stocked at
high densities
40
32.
Percent crabs shed and crab mortality for the protein
skimmer stocked at high densities (July-August, 1984)
41
ix
X
LIST OF TABLES
Table
1.
Correlation coefficients comparing crab population
variables with physical and chemical water quality
parameters for the protein-skimmer system stocked
at high densities, days 557-574
43
2.
Correlation coefficients comparing crab population
variables with nitrogen and microbiological quality
parameters for the protein-skimmer system stocked
at high densities, days 557-574
44
xi
xi i
INTRODUCTION
Georgia has not been immune to the heightened interest in
shedding blue crabs that has developed along the southeast and
Gulf coasts in the last few years. The small initial capital
investment attracted crabbers, fishermen, and other small
businessmen. Potential shedders, particularly those interested in
closed recirculating seawater shedding systems, requested
assistance from The University of Georgia Marine Extension
Service. The following study was initiated to develop baseline
water quality data for closed, recirculating soft shell crab
shedding systems.
The Marine Extension Service Analytical Services Laboratory
began a project in May 1983 to monitor chemical and microbiological water quality of two commercial soft shell crab shedding
systems operated by a south Georgia crabber. The first recirculating seawater system consisted of two 4 ft. x 8 ft. x 1 ft.
fiberglass-coated plywood tanks, a 4 ft. x 4 ft. x 2 ft. sump, and
a 4ft. x 4ft. x 1 ft. biological filter holding 200 pounds (90.7
kg) of crushed Florida coral that was produced by Carib Sea, Inc.
(Miami, Florida). The owner completed a second closed, recirculating system in July 1984. It incorporated a 10ft. x 8 in.
cylindrical PVC protein skimmer, four 8ft. x 3ft. x 1 ft.
fiberglass shedding tanks, and a 4 ft. x 4 ft. x 5 ft. combination
biological filter and sump that held 24 bushels (0.8 mJ) of old
oyster shells (Osterling, 1984). Water was circulated in both
systems by 3/4 hp electric motors driving 1-1/4 in. pumps. Two
inlet pipes with venturi tubes for aeration circulated water in
each holding tank. The biological-filter system and the proteinskimmer system held approximately 440 gallons (1,666 liters) and
610 gallons (2,309 1 iters) of seawater, respectively.
METHODS
The operator maintained control of the shedding systems.
Crabs were added and sheds removed as determined by peeler
supplies and market conditions. The owner kept records of total
crabs, sheds, and mortality. All additional data was collected by
the laboratory staff.
Water samples for chemical and microbiological analyses were
collected at the outlet of the biological-filter system from May
4, 1983, through August 1, 1983. Water samples were taken from
the inlet and the outlet of the protein-skimmer system from July
11, 1984, through August 28, 1984. Inlets and outlets in both
systems were sampled between September 2S, 1984, and October 6,
1984. Sample collections were specified by Julian dates running
consecutively for two years, numbering 1-730.
The following physical and chemical parameters were measured
for single samples: temperature, salinity (American Optical handheld refractometer), pH (American Public Health Association,
1981 ), carbon dioxide (Hach Chemical Company, 1983), MPN total
col iforms (American Public Health Association, 1981 ), and MPN E.
coli (American Public Health Association, 1981). The followingdetermined in duplicate: dissolved oxygen (American Public
Health Association, 1981); percent oxygen saturation (Strickland
and Parsons, 1968); biological oxygen demand (American Public
Health Association, 1981); ammonium (Martin, 1972); ammonia (Bower
and Bidwell, 1978); nitrate (Mullin and Riley, 19SS); n-itrite
(American Public Health Association, 1981); total alkalinity (U.
S. Environmental Protection Agency, 1979); calcium (U. S.
Environmental Protection Agency, 1979); and marine agar plate
counts (Schleper, 1972). Total alkalinity, calcium, and carbon
dioxide levels were not determined for 1983 biological-filter
samples.
were
The operator documented the total number of crabs, total
sheds, and total mortality for the protein-skimmer system during
July and August, 1984. Although complete records were not
available for the three remaining- operating conditions, the
following categories were definedz
(1)
Biological Filter Stocked at High Densities, >SO crabs
per system per day, (May-June, 1983)
(2)
Protein Skimmer Stocked at High Densities, >SO crabs per
system per day, (July-August, · 1984)
(3)
Biological Filter Stocked at Low Densities, <SO crabs
per system per day, (September-October, 1984 )
(4)
Protein Skimmer Stocked at Low Densities, <SO crabs per
system per day, (September-October, 1984)
The General Linear Regression Model of the Statistical
Analytical System (SAS) (Ray, 1982) was used to perform
correlation procedures on protein-skimmer data generated when the
system was densely stocked. Four variables -crabs added, crabs
shed, total crabs, and dead crabs- were compared with all
chemical and physical parameters determined during that portion of
the study. A SAS GLM ANOVA procedure compared inlet and outlet
samples for all monitored parameters in each system (Ray, 1982).
2
In the remainder of the paper, ''significant 11 will refer to
statistical results wi th p < 0.05.
RESULTS
Biological Filter
Figure 1 details changes in pH, temperature (°C), and
salinity (ppt) for biological-filter outlet samples collected from
May-July, 1983 (high-density stocking) and Figure 2 does the same
for inlet and outlet samples collected during September and
October, 1984 (low-density stocking). ~ater temperatures
increased during the summer and decreased in the fall. Salinity
levels gradually increased from 11 ppt (day 124) to 27 ppt (day
205) for high-density stocking of the biological-filter system.
Salinity concentrations for low-dens i ty stocking varied randomly
and ranged from 17.5 to 20.5 ppt. Dissolved oxygen (0 2 mg/1 ) and
biological oxygen demand (BOD mg/1) levels determined for dense
crab populations are presented in Figure 3. Carbon dioxide
(mg/1 ), 0 2 (mg/1 ), BOD (mg/1 ), calcium (mg/1 ), and alkalinity (mg
Caco /l) concentrations determined for low crab densities are
3
shown in Figures 4 and 5. BOD levels were greater for high crab
populations than for low populations. Disso1ved oxygen levels
were depressed from Julian dates 146 to 180 (Figure 3) . Oxygen
saturations were consistent at both stocking densities (Figures 6
and 7).
Figures 8, 9, and 10 show nitrogen compound levels for the
biological filter operating under dense and sparse crab
populations. No consistent differences or concentration patterns
were noted for ammonium (NH4) or ammon i a ( NH 3 ) levels. Nitrate
(N0 3 ) concentrations increased rapidly when the system w~s stocked
at low densities, ranging between 189 ~g/1 and 3.95 x 10 ~g/1
(Fkgures 7 and 8). High density N0 3 levels increased from 1.22 x
10 ~g/1 (day 133) to a maximum of 1.62 x 10) ~g/1 ( day 197) and
returned to 1.50 x 10S ~g/1 (day 208) (Figure 6). Nitrite levels
decreased for dense crab populations and demonstrated an inverse
relationship to nitrate levels on ~11 occasions. Nitrite
concentrations peaked at 1.97 x 10 ~ g/1 for high-density samp les
and at 17 ~ g/1 for low-density samples (Figures 8, 9 , and 10 ).
Microbiological populatio~s determined by marine agaB plate
counts ranged between 2.2 x 10 organisms/ml and 1.0 x 10
organisms/ml for densely ~tocked samples and between 8.5 x 103
organisms/ml and 1.2 x 10 organisms/ml for the sparsely stocked
trial (Fi gures 11 and 12). Coliform and E. coli levels showed no
3
consistent patterns (Figures 13 and 14). No significant
differences were determined between inlet and outlet values for
all monitored chemical, physical, and microbiological parameters.
Protein Skimmer
Temperature (°C) and pH data presented in Figures 15 and 16
for the prote in-ski mmer system exhibited no major trends during
sparse and dense stocking. Temperatures were within expected
seasonal variations. Salinity levels gradually increased from 13
ppt (day 557) to 16 ppt (day 574) during high-density stocking of
the protein-skimmer system (Figure 15). Salinity concentrations
varied randomly for low-density stocking and ranged from 17 to 19
ppt (Figure 16). Oxygen levels remained between 6 mg/1 and 8 mg/1
during the summer (Figures 17 and 18) and increased to a maximum
concentration of 9.4 mg/1 in the fall (day 642) (Figures 19 and
20). Alkalinity levels rapidly fell from an initial value of 125
mg Caco /1 (day 557) (Figure 17) and leveled off at approximately
3
70 mg Caco /1 for the rest of the study (Figures 17, 18, 19, and
3
20). Calc1um levels decreased from an initial mean inlet and
outlet level of 101 mg/1 (day 557) for high-density stocking to a
minimum value of 80 mg/1 (day 559) then continued to increase for
the remainder of the study, reaching a maximum mean concentration
of 240 mg/1 (day 643) during low-density stocking (Figures 17, 18,
19, and 20). BOD levels ranged between 0.69 mg/1 and 6.33 mg/1,
but no consistent pattern was observed (Figures 17, 18, 19, and
20). Oxygen saturation ranged between 78.4% and 100.0% for inlet
and outlet samples (Figures 20 and 22). Saturation values
increased between days 635 and 644 when the system was stocked at
low densities (Figures 21 and 22).
Recorded ammonium concentrations ranged between 31 ~g/1 and
686 ~g/1. No trends were discernible (Figures 23, 24, 25 and 26).
Ammonia concentrations peaked at 23 ~g/1 (day 557). The lowest
value, 0.3 ~g/1, was recorded on day 641. Nitrates accumulated in
the protein-skimmer system over time, regardless of stocking
densities (Figures 23, 24, 25, and 26). Nitrite levels ranged
between 100 ~g/1 and 810 ~g/1 for dense crab populations. Nitrite
levels determined for the sparsely stocked system decreased
rapidly from 338 ~g/1 (day 633) to 10 ~g/1 (day 639) and stayed
below 20 ~g/1 for the remaining samples (Figures 23, 24, 25 and
26).
Marine agar plite count populations ranged between 10 4
organisms/ml and 10 organisms/ml for both stocking levels
(Figures 27 and 28). MPN total coliform organisms showed no
consistent pattern, ranging from 68 organisms/100 ml to 16,000
organisms/100 ml (Figures 29 and 30). MPN E. coli levels ranged
between none detected and 490 organisms/100-ml-rffgures 29 and
4
30). No significant differences were determined between inlet and
outlet values for all monitored chemical, physical, and microbiological parameters.
Figure 31 presents the number of added, shed, dead, and total
crabs in the protein-skimmer system stocked at high densities.
Total crab populations ranged from 50 to 165 during 16 days of
operation. The percentage of successful sheds registered between
15.9% and 97.1% (Figure 32). Mortality figures were low, ranging
from 1.5% to 8.1%.
Protein Skimmer Versus Biological Filter (High Density)
The protein skimmer and biological filter systems had similar
responses to temperature (°C), salinity (ppt), pH, oxygen
concentrations (mg/1), percent oxygen saturation, and BOD levels
(mg/1) (Figures 1, 3, 6, 15, 17, 18, and
Biological filter
ammonium levels (NH 4 ) fell from 5.12 x 10 ~g/1 (day 124) to 31
~g/1 (day 133).
Biological-filter ammonium levels were less than
protein-ski mmer concentrations for all but the initial sample.
Protein-skimmer ammonium levels ranged from 126 ~g/1 to 686 ~g/1
for the densely stocked system. Ammonia (NH ) levels followed a
3
similar pattern with biological-filter concentrations decreasing
rapidly from 287 ~g/1 (day 124) to 2 ~g/1 (day 138). The minimum
recorded ammonia level was 0.5 ~g/1 (day 187). Protein-skimmer
levels ranged between 2.6 ~g/1 and 23 ~g/1 (Figures 8, 23, and
24).
F).
Nitrate levels were high in both systems, with peaks
exceeding 1 x 105 ~g/1. Nitrite concentrations decreased with
time in the biological system (1.97 x 103 ~g/1 to 49 ~g/1 ), while
nitrate levels increased. Protein-skimmer nitrite values varied
randomly and ranged from 100 ~g/1 to 810 ~g/1.
Biological-filter marine agar plate counts ranged from 8.80 x
103 organisms/ml to 1.00 x 108 or~anisms/ml, while protein-s~immer
populations ranged from 6.85 x 10 organisms/ml to 3.73 x 10
organisms/ml (Figures 11, 27, and 28). No pattern was observed
for coliform or E. coli populations in either system (Figures 13
and 29).
- -Protein Skimmer Versus Biological Filter (Low Density)
There were no consistent differences in pH, temperature (°C),
salinity (ppt), carbon dioxide (mg/1 ), or BOD (mg/1) levels
between both systems stocked at low densities (Figures 2, 4, 5,
16, 19, and 20). Biological-filter calcium levels were
consistently lower (range- 103 mg/1 to 132 mg/1) than proteinskimmer concentrations (range- 201 mg/1 to 240 mg/1 ). Alkalinity
5
values were reversed with protein-skimmer concentrations falling
between 67 mg Caco /1 and 86 mg CaC0 1 /1, while biological levels
3
ranged between 106 mg Caco /1 and 131 mg Caco /1 (Figures 4, 5,
3
3
19, and 20). Dissolved oxygen levels were similar in both systems
except for a minimum value of 3.75 mg/1 for the biological filter
on day 634 following a pump failure (Figures 4, 5, 19, and 20).
Oxygen-saturation values exhibited the same pattern (Figures 7,
21, and 22).
Both systems' ammonium (NH4) concentrations were similar.
Protein-skimmer ammonia (NH 1 ) concentrations were lower (range0.3 ~g/1 to 3.5 ~g/1) than 6iological-filter levels (range- 0.4
~g/1 to 15 lJg/1) (Figures 9, 10, 25, and 26).
Biological nitrate
levels increased with time (range- 1.84 x 103 lJg/1 to 3.95 x 10 4
~g/1), but remained much lower than pcotein-skimmer concentrations
(range- 2.20 x 105 lJg/1 to 2.49 x 10) lJg/1 ). Biological nitrite
concentrations (range- 6 ~g/1 to 17 lJg/1) were less than proteinskimmer levels (range- 10.5 llg/1 to 1.92 x 10..5 lJg/1) (Figures 9,
10, 25, and 26). Marine agar plate count populations decreased
with time for both systems, but biolo9ical-f~lter populations
(range- 8.5 X 103 organisms/ml to 1.22 X 10 or~anisms/ml) were
less than protein-skimmer populations (1.64 x 10 organisms/ml to
3.31 x 10 6 organisms/ml) (Figures 12 and 28). No trends or
differences were noted for total coliform or E. coli levels
--(Figures 14 and 30).
Protein-Skimmer High-Density Crab Correlations
The only complete record of total crabs, shed crabs, added
crabs, and crab mortality was available for the protein-skimmer
system stocked at high densities. Crab population levels are
presented in Figure 31 (days 557-574). Correlations determined
for total crabs, added crabs, shed crabs, and dead crabs and the
monitored physical, chemical, and microbiological parameters are
presented in Tables 1 and 2 (Ray, 1982). Although not signif icant
at the 0.05 level, two parameters exhibited strong negative and
positive correlations between crabs added to and shed in the
system, respectively. Ammonia concentrations correlated
negatively (p = 0.059) with crabs added to the system while
alkalinity showed a positive correlation (p = 0.056) with crabs
shed (Tables 1 and 2). All correlations referred to in the
remainder of the paragraph were significant, p < 0.05. A positive
correlation was determined between total crabs and the carbon
dioxide content of the water (Table 1 ). Negative correlations
with crab sheds were determined for salinity and nitrate levels
(Tables 1 and 2).
6
DISCUSSION
Both filters maintained dissolved oxygen levels that exceeded
the minimum 4 mg/1 needed to support crab and filter metabolisms
on all but one occasion (Osterling, 1984). The biological-fi lter
system fell to 3.7 mg 0 2 /1 following a pump failure. However,
recent work by Manthe et al. (1984) suggests that acceptable
dissolved oxygen levels in the shedding tanks (5.6 mg/1) provided
only 2.0 mg/1 dissolved oxygen to the biological filter. Low
oxygen levels act as the limiting factor for biological oxidation
of nitrogen compounds. Additional filter oxygenation could
increase efficiency.
Nitrate levels were hi%h in both systems, with the biological
filter peakigg at 1.93 x 10 ~g/1 and the protein skimmeS peak ing
at 2.49 x 10 ~g/1. Neither system reached the 3.6 x 10 ~g/1
level that Manthe et al. (1984) proposed as an approximate upper
safety limit for shedding blue crabs; however, a significant
negative correlation was deter~ined between nitrate concentrations
and the number of crabs shed when the protein-skimmer system was
stocked at high densities. Both nitrate levels were within the
same orders of magnitude (ranging from 2.14 x 10' ~g/1 to 3.50
~g/1) reported for closed systems monitored by Malone et al.
(1984). Protein-skimmer nitrite levels were generally greater
(ranges: high de~sity- 100 ~g/1 to 810 ~g/1; low density- 10.5
~g/1 to 1.92 x 10 ~g/1) than the biological-~ilter concentrations
(ranges: high density- 49 ~g/1 to 1.97 x 10 ~g/1 ; low density6 ~g/1 to 17 ~g/1 ), although biological-filter nitrite peaks
exceeded protein-skimmer levels on occasi~n. The peak biologi calfilter nitrite concentration of 1.97 x 10 ~g/1 occurred on the
first day of sampling, prior to complete co nditioning of the
filter. The level was less than the 2.0 x 10' ~g/1 nitrite
concentration reported by Malone et al. (1984) for an overstocked
and failing closed, recirculating shedding system. Nitrite levels
decreased rapidly after the first day and remained below protjinskimmer concentration s. Neither system exceeded the 2.0 x 10
4 ~g/1
~g/1 toxic nitrite limit for molting crabs or the 2.0 x 10
toxic limit for intermolt crabs (Manthe et al. 1984). Proteinskimmer ammonium (NH4) and ammonia (NH 3 ) levels stabilized above
bi~logical-filter concentrations, but neither system reached 7 x
10 ~g NH 3/l, the concentration toxic to peeler crabs (Osterling,
1984). Maximum recorded ammonia concentrations for the
biological-filter system and protein-skimmer system, respjctively,
3.5 ~g/1 and 14.6 ~g/1, were much less than the 5.00 x 10 ~g/1
reported by Malone et al. (1984).
The biological filter maintained lower calcium concentrations
(range- 103 mg/1 to 132 mg/1) than the protein skimmer (range-
7
201 mg/1 to 240 mg/1) when stocked at low densities. Alkalinity
levels showed the opposite effect, with biological-filter values
ranging from 106 mg Caco 11 to 131 mg Caco 3/l and protein-skimmer
3
levels ranging from 67 mg Caco 311 to 86 mg CaC0 3/l. Both oystershell (protein-skimmer) and coral (biological) filters maintained
greater alkalinity levels than those reported by Malone et al.
(1984), 70 mg Caco /l to 30 mg Caco 11, for a clam shell,
3
3
dolomite, and activated carbon filter. Although not significant,
the number of crabs shed had a strong positive correlation with
alkalinity levels (Table 1).
Two significant negative correlations were determined between
crabs shed and salinity and nitrate levels when the protein
skimmer operated at high densities. Salinity levels ranged
between 13 and 16 ppt. Nitrate levels ranged from 672 ~g/1 to
1.51 x 10S ~g/1 and were below concentrations reported toxic to
intermolt and molting crabs. Positive correlations between total
crabs and carbon dioxide levels were indicative of system stress
resulting from increased crab populations and their waste
met abo 1 i tes.
CONCLUSIONS
Nitrate, nitrite, and ammonium concentrations remained below
accepted toxic limits for molting blue crabs in both the proteinskimmer and biological-filter systems. However, a significant
negative correlation was established between nitrate
concentrations and the number of crabs shed in the protein-skimmer
system. Ammonium, ammonia, and nitrite levels were generally
greater in the protein-skimmer system than in the biologicalfilter system.
The oyster-shell filter of the protein-skimmer system
produced calcium levels that exceeded and alkalinity levels which
were less than those determined for the crushed-coral medium of
the biological-filter system. The efficiency of the crushed-coral
biological filter increased with time and conditioning as
evidenced by decreasing nitrite levels.
8
FIGURES
9
BIOLOGICAL FILTER OUTLET
May - July 1983 (HI&h Density)
32
30
..
ll.
ll.
.....
:>,
d
.......
II
(/)
28
26
24
J
/
~
t\ ''\ \
22
18
c"
16
Q
14
12
10
8
...
~
~
~
20
u
ll.
=
j
J
J(
~
-I
.....,
EJHS
as s.a-sss s -as s -8
180
2 00
6
120
140
0
pH
Figure 1.
+
160
J ulian Date 1983 - 1984
¢
Temperature
Salinity
Outlet pH, temperature (°C), and salinit y
(ppt) levels for the biological fi Iter stoc ked
at high densities ( May-July, 1983)
10
220
BIOLOGICAL FILTER INLET-OUTLET
September-October 1984 (Low Density)
22
21
20
19
...g,
g,
18
......1>.
17
II
0'1
1~
......."
16
14
0
..
13
Q
12
:I:
11
II
g,
10
9
8
7
63~
633
639
637
64-1
643
Julian Date 1983-1984
D
pH-I
+
Figure 2.
T-1
0
S-1
6
pH-0
X
T-0
v
Inlet and outlet pH, temperature (°C), and
salinity (ppt) levels for the biol-ogical filter
stocked at low densities (September-october,
1984)
11
s-o
BIOLOGICAL FILTER OUTLET
8
May - July 1983 (H!'h Density)
---
-.-
I
~
7
....
\
Ill
a
~
-
6
-
5
-
4
-
'/t~Jv~
j,
-
2
-
1
-
\
r
11
],- t'J,: J~
i;
~
~
j\
•
\
-\
3
~
~
f
~
!!J
\
'
~\
II
+
0
120
140
0
Figure 3.
160
180
200
J ulian Date 1983 - 1984
Dissolved 02
...
BOD
Outlet dissolved oxygen and BOD leve ls
for the biological filter stocked at high
densities (May-July, 1983)
12
220
BIOLOGICAL FILTER INLET
September- October 191J4. (Low Density)
158.4
~
~
t:.
100
t:.
~
63. 09
3g,91
25.11
15.84
\
•a
10
6. 309
3. 981
2.511
X
1.51J4.
1
0.630
0.398
1
633
D
02
Figure 4.
X
X
6'YI
635
+
C02
639
Juli an Date 1983-1984
~
t:. Ca
Alk.
X
IJ4.1
643
X
BOD
Mean inlet dissolved o2 , dissolved
C0 2 , alkalinity, calcium, and BOD
levels for the biologica l f ilter stocked at
low densities (September-october, 1984)
13
BIOLOGICAL FILTER OUTLET
September-October 1984 (Low Dens ity)
1l58.-'
ll
<>
100
ll
<>
83.09
39.81
2l5.11
1l5. U
\
s•
10
8.309
3.981
I
2. l511
1.C5U
1
0.830
l
X
~/
v
833
D
63l5
+
02
Figure
5.
637
C02
639
Juli an Date 1983-198-'
ll
Ca
<> Alk.
X
X
8-'1
643
X
BOD
Mean outlet dissolved 0 2 , dissolved
C0 2 , alkalinity, calcium, and BOD
levels for the biological fi l ter stocked at
low densities (September-October, 198~ )
14
BIOLOGICAL FILTER OUTLET
May - July 1983 (H!ch Density)
t10
tOO
~
....
0
90
II
.."'
;j
II
Ill
80
l\1
0
..
70
~
II
u
a.'"'
60
120
140
160
D
Figure 6.
180
JuHan Date 1983- 1984
7. OZ Saturation
Mean outlet oxygen-saturation levels for
the biological filter stocked at high
densities (May-July, 1983)
15
zoo
220
BIOLOGICAL FILTER INLET-OUTLET
September- October 1984 (Low Density)
100
90
...a
0
II
k
80
.
:I
II
II
N
70
..a
0
•k
(J
80
•
Po
50
633
635
D
Figure
7.
7. 02- lnlet
639
637
M1
Julian Date 1983-1984
+ 7. 02-0utlet
Mean inlet and outlet oxygen-saturation levels
for the biological filter stocked at low
densities (September-October, 1984)
16
BIOLOGICAL FILTER OUTLET
May- July 1983 (HI &h Density)
1000000
100000
10000
~
\.,
e
•
"•
.."
1000
0
0
100
~
10
0.1
160
140
120
0
NH4
Figure 8.
+
180
Julian Date 1983 - 1984
NH3
o N03
A
200
N02
Mean outlet ammonium (NH 4 ), ammonia
( NH ) , nitrate ( N0 3 ), and nitrite ( N0 2 )
3
levels for the biological filter stocked
at high densities (May-July, 1983)
17
BIOLOGICAL FILTER INLET
September- October 1984 (Low Dens! ty)
100000
~
10000
t
I
I
I
I
....
1000
\
I
II
e
I
----
Ill
..
I<
100
0
I<
...u
~
10
-1
I
0. 1
637
63~
633
o
Figure 9.
NH4
+
639
Julian Date 1983-1984
0
N03
NH3
641
ll
N02
Mean i nlet ammonium (NH4), ammonia (NH 3 ),
nitrate (N0 1 ), and nitrite ( N0 2 ) levels
for the biological filter stocked at low
densities (September-October, 1984)
18
643
BIOLOGICAL FILTER OUTLET
September-October 1984- (Low Density)
100000
10000
...
1000
~
1
....
\
ll
e
i
"'0at
..."'
100
()
~
10
1
0.1
I
~--
--'
--+
~I
I
I
635
633
0
NH4
Figure 10.
637
+
639
Julian Date 1983-1984
0
N03
NH3
64-1
ll
N02
Mean outlet ammonium (NH 4 ), ammonia
(NH ), nitrate (No 3 ), and nitrite (N0 2 )
3
levels for the biological f il ter stocked
at low densities (September-October, 1984)
19
643
BIOLOGICAL FILTER OUTLET
May- July 1983 (Hich Density)
3. 16B+08
I
I
1.00B+08
-;
3. 16E+07
1.00B+07
l
3. 16B+ 06
....,
-<
s
\
~
I
....
~
I
I \
n
.a
n
1.00B+06
~
•
Cit
I<
3.16B+05
0
i
l
I
1.00B+05
l
3.16E+04
""1
1.00E+04
--1
I
~
~}.5 ~J
I
rb
~
t!J
I
3.16B+03
120
140
0
Figure 11.
160
180
200
Julian Date 1983 -1 984
Mari ne Agar
Mean outlet marine agar plate counts
for the biological filter stocked at h i gh
densities (May-July, 1983 )
20
220
BIOLOGICAL FILTER INLET - OUTLET
September- October 1984 (Low Dens i ty)
1.268 + 05
1.008 + 05
~'
7.94E + 04
6.31E+ 04
5 .01E + 04
....
3.988 + 04
-I
3.168 + 04
l
....fl
2.51E + 04
l
II
2. 00E + 04
e
\
e
fl
c
"'
\
\
\
\
\
Ql
0
\
~
'\
\'
1.568 + 04
1.268 + 04
1. 008 + 04
7. 94E + 03
6. 31E + 03
5. 01E + 03
/
j
633
0
635
Marine Agar - !
Figure 12.
637
639
/
'
/
641
J ul1an Date 1983 - 1984
+ Mar i ne Agar - 0
Mean inlet and outlet marine agar plate
c ounts for the biological filter stocked at
low densities (September-October, 1984)
21
643
BIOLOGICAL FILTER OUTLET
May - July 1983 (High Density)
10
9
8
...
s
7
,.....
'
-;
6
J
5
1
flE-o
ll"V
4
~
0
3
0
II
~
tl
O"Cf
\
s
..
II II
II
;j
0
'"'.d
,..•
2
I
-1
~
[!]
0
120
140
0
MPN Col!forms
Figure 13.
160
180
200
Julian Date 1983-1984
..MPN E. col!
MPN total coliform and MPN E. coli outlet
populations for the biological-riTter stocked
at high densities (May-July, 1983)
22
220
BIOLOGICAL FILTER INLET-OUTLE.T
September - October 1984 (Low Density)
6
5
~
\
....
s
4
1""\
0 II
O'!j
.... l:l
\
.,
ll ll
e :1
\
3
ll 0
... .d
l:le--
\\
\
\
\
11'-1
...
"'
0
'
I
I
*
0
633
0
ColL - I
635
+
Figure 14.
E. coli - !
;
4>
637
639
Juli an Date 1983-1984
0
Coll.-0
641
!:;
643
E. coll - 0
MPN total coliform and MPN E. coli inlet
and outlet populations for the biological
filter stocked at low densities ( SeptemberOctober, 1984)
23
j
PROTEIN - SKIMMER INLET - OUTLET
July - Aucust 1984 (H1ch Density)
26
25
24
23
...
22
llo
llo
21
20
......>.
19
ll
.......
18
tl
Ul
17
16
u
15
"c
14
Q
13
:cllo
12
11
~
'9
v
'9
'9
'9
10
I
~
9
8
7
557
D
pH - I
559
+
Figure 15.
561
563
567
565
569
Jullan Date 1983- 1984
T- 1
~
S-1
t:.
pH - 0
X
573
571
T- 0
v
Inlet and outlet pH, temperature (°C), and
salinity (ppt) levels for the protein skimmer
stocked at high densities (July-August, 1984)
24
s-o
PROTEIN - SKIMMER INLET - OUTLET
September-October 1984 (Low Density)
21
20
19
18
~
a.
a.
17
>.
...
s::
.......
16
~
15
•
O'l
14
u
13
..•
12
Cl
11
=
c.
10
9
8
7
635
633
0
pH - 1
+
Figure 16.
T- 1
637
<>
639
Julian Date 1983- 1984
t.
pH- 0
S-1
X
T-0
Inlet and outlet pH, temperature (°C), and
salinity (ppt) levels for the protein skimmer
stocked at low densities (September-October,
1984)
25
7
s-o
PROTEIN -SKIMMER INLET
July-Au&ust 1984 (Hl&h Density)
1!58.4~
100
ll
ll
ll
0
0
0
ll
~
0
63.09
39.81
I
2!5.11
1!5. 84.
\
s•
10
l
I
J
6.309
3.98 1
2.!511
1.~84
1
0.630
lI
l
I
~
~
X
X
X
I
X
I
X
j
j
5~9
5!57
D
I
X
02
Figure 17.
561
+
C02
563
!565
567
Julian Date 1983-198 ..
0
ll
Alk.
Ca
569
!571
X
Mean inlet dissolved 0 2 , dissolved C0 2 ,
alkalinity, calcium, and BOD levels for
the protein skimmer stocked at high
densit i es (July-August, 1984)
26
BOD
I
573
PROTEIN -SKIMMER OUTLET
July-Auaust 1984 (Btah Dens tty)
108.41:.
100
1:.
~
~
1:.
1:.
~
~
X
X
63.09
39.8 1
20. 11
10.84-
\
•a
10
6.309
3.981
2.011
1.!584
1
0.630
0.398
~
X
X
X
~
l
I
!507
!5!59
!561
!563
!56!5
!567
!569
!57 1
Jultan Date 1983-1984
D
A
02
Figure 18.
+
C02
~
Alk.
1:.
Ca
X
BOD
Mean outlet dissolved 0 2 , dissolved C0 2 ,
alkalinity, calcium, and BOD levels for
the protein skimmer stocked at high
densities (July-August, 1984 )
27
!573
PROTEIN- SKIMMER INLET
September-October 1984 (Low Density)
2!51.1
b
H58. 4.
100
63.09
39.81
2~.11
\
s•
1~.84
10
6.309
3.98 1
2.~11
1.!584.
X
X
1
X
0.630
83~
633
0
02
Figure 19.
+
637
C02
639
Julian Date 1983-1984.
¢
AUt.
b
Ca
841
84.3
X
Mean inlet dissolved 0 2 , dissolved C0 2 ,
alkalinity, calcium, and BOD levels for
the protein skimmer stocked at low
densities (September-October, 1984)
28
BOD
PROTEIN- SKIMMER OUTLET
September- October 198'- (Low Density)
2!51.1
6.
1:!.
1!58.4
100
63.09
39.8 1
...
2!5.11
a•
1!5.84
\
10
6.309
X
3.98 1
2.!511
X
1.!584
633
D
63!5
02
Figure 20.
+
637
C02
X
X
639
641
Julian Date 1983-1984
0
6.
Alk.
Ca
6~
X
BOD
Mean outlet dissolved 0 2 , dissolved C0 2 ,
alkalinity, calcium, and BOD levels for
the protein skimmer stocked at low
densities (September-october, 1984 )
29
PROTEIN -SKIMMER INLET-OUTLET
July-Aucust 1984 (Hi ch Density)
102
100
98
a
......0
II
...II"'~
96
94
92
Ill
N
90
0
...
a
88
u
86
a."'
8-4,
I
I
82
80
78
~57
559
D
Figure 21.
561
7.02 - Inlet
563
565
567
569
571
Julian Date 198 3-1984
+ 7.02- 0utlet
Mean inlet and outlet oxygen-saturation levels
for the protein skimmer stocked at high
densities (July-August, 198~)
30
573
PROTEIN -SKIMMER INLET-OUTLET
September- October
198-l (Low Density)
97
96
95
9-l
a
.....0
tl
I<
..
93
92
::1
tl
ITJ
Ill
0
..a
I
0
I<
I
a.
91
90
89
88
87
86
85
84
83
633
635
0
Figure 22.
7.02-lnlet
639
637
641
643
Julian Date 1983-1984
+ 7.02- 0u tlet
Mean inlet and outlet oxygen-saturation levels
for the protein skimmer stocked at low densities
(September-Oc tober, 1984)
31
PROTEIN - SKIMMER INLET
July-Au&ust 1984 (H1&h Density)
316227
100000
31622.
\
10000
....
\
3162.2
II
a
II
.."'
0
.."'
::g
1000
\_
316.22
u
100
31.622
10
3.1622
1
]
557
559
o
Figure 23.
5 61
NH4-
565
563
+
567
Juli an Date 1983 - 1984NH3
¢
N03
569
A
571
N02
Mean inlet ammonium ( NH 4 ), ammonia (NH ),
nitrate ( No ) , and nitrite ( N0 2 ) levels3
3
for the protein skimmer stocked at high
densities (J uly-August, 1984 )
32
573
PROTEIN - SKIMMER OUTLET
July-Aucust 1984 (H1ch Density)
316227
100000
31622.
10000
\
II
a
3162. 2
II
..w
1000
0
w
...u
316.22
:8
I
100
I
i
31.622
10
3. 1622
557
559
0
561
NH4
Figure 24.
565
563
+
567
Julian Date 1983-1 984
NH3
<>
N03
569
A
571
573
N02
Mean outlet ammonium ( NH ), ammonia ( NH ) ,
4
nitrate (No 3 ), and nitrite (N0 2 ) levels 3for
the protein skimmer stocked at high densities
(July- August, 1984)
33
PROTEIN - SKIMMER INLET
September- October 1984 (Low Density)
1E+06
100000
10000
\
II
s•
1000
.."
:g
100
II
•0
u
10
1
0.1
635
633
637
639
Julian Date
0
Figure 25.
NHol
+
o
NH3
64.1
19 83-19 8~
N03
6
NOZ
Mean inlet ammon ium (NH 4 ) , a~onia (NH ),
nitrate (N0 1 ), and nitrite (N0 2 ) levels3
for the protein skimmer stocked at low
densities (September-October, 1984)
34
64.3
PROTEIN-SKIMMER OUTLET
September-October 1984- (Low Density)
1E+06
100000
10000
\
•a
..
•"
.."
1000
0
0
~
100
~
10
J
1
0. 1
633
635
639
637
64-1
JuHan Date 1983-1984-
D
Figure 26.
NH4
+
NH3
¢
N03
A
N02
Mean outlet ammonium (NH4)• ammonia (N H ) ,
nitrate (N0 1 ) , and nitrite (N0 2 ) levels 3
for the protein skimmer stocked at low
densities (September-October, 1984)
35
64-3
PROTEIN -SKIMMER INLET - OUTLET
July-Aucust 1984- (H1ch Density)
3.98B+06
3. 16B+06
<UI1B+06
2.00B+06
1.58B+06
1.268 +06
...
a
\
II
1.008+06
7 .94,!+05
6.31!+05
a
II
5.01!+05
11
3.98B +05
•
3. 168+05
...,
"
0
2.51!+05
2.008+05
1.588+05
1.26'8+05
1.008+05
7.94,!+04,
6.31!+04,
557
559
561
563
565
567
569
571
JuUan Date 1983-1984-
D
+
lhr1ne Aaar -1
Figure
27.
lhrtne Aaar-0
Mean inlet and outlet mar i ne agar plate
counts for the protein skimmer stocked at h i gh
densit ies (July-August, 1984)
36
573
PROTEIN -SKIMMER INLET-OUTLET
September-October 1984- (Low Density)
3.98E+06
2.!51!!+06
1.!58B+06
1.00E+06
...
6.31!+05
s•
3.98B+05
a
\
..
II
2.!51!+05
d
••..
0
1.58!+05
1.00B+05
6.31!!+043.98B + 042.511H041.58B+04633
0
635
Marine A&ar-1
Figure 28.
637
639
64-1
Julian Date 1983-1984+ Marine A&ar - 0
Mean i nlet and outlet marine agar plate
counts for the protein skimmer stocked at low
densities (September-october, 1984)
37
64-3
PROTEIN -SKIMMER INLET-OUTLET
July-Au cust 1984- (H1c h Density)
10
9
...
a,.....
7
0 •
0'!1
6
•a •:1
5
.
..."
... a
\
• 0
.. .d
aE-<
-...;
..
0
3
\
\
z
\
1
0
557
0
ColL-I
559
561
+
Figure 29.
B. col1-I
563
565
Juli an Date
0
567
569
571
1983 - 198~
Coll.-0
6
E. coli-0
MPN total coliform and MPN E. coli inlet
and outlet populations for the protein
skimmer stocked at high densities
(July-August, 1984)
573
PROTEIN -SKIMMER INLET-OUTLET
September-October 1984 (Low Density)
.
16
15
1413
..e
12
11
,....
10
.. a
9
0 •
0'tl
\
I
Ill
••
a• 0='
8
lllv
6
"'
5
.. .d
t:l(-1
•
0
7
I
..
3
2
0
633
0
ColL- I
635
+
Figure 30.
B. coU- I
637
639
JuUan Date 1983-1984
o Coll.-0
641
ll
MPN total coliform and MPN E. col i inlet
and outlet populat i ons for the protein
skimmer stocked at low densit ies
( September-October, 1984 )
39
643
B. coU-0
PROTEIN - SKIMMER CRABS
: : r150
l \
130
-,
1ZO
~
110
July-Aucust 1984- (H1ch Density)
----I
I
J
II
,Q
•
k
u
557
D
559
560
Added
Figure 31.
561
56Z
+
563
564-
565
566
567
J ulian Date 1963 - 1964
Shed
¢
Dead
568
569
tl
570
571
Total
Total crabs, total crabs added, total
crabs shed, and total dead crabs for the
protein skimmer stocked at high densities
(July-August, 1984)
40
57Z
573
PROTEIN - SKIMMER CRABS
July - Aucust 1984- (Hi ch Density)
1007.
~
907.
-1
807.
-1
I \
I\
707. __.
II
..a"'
607.
~
I
u
507.
u
k
II
I
l
II
I
:'\
II
,Q
I
_j
207.
~
I
VI
~
r:;::
557
559
561
0
Figure 32 .
I
\
\
\
\
\
r::=;= .
562
"'=
563
Shed
564-
/
~~
~........
~
560
~
\
107. __.
07.
\
I
v \
en
307.
\
\~
I
4-07. -"1
0..
\
\
565
566
---t"""
567
568
:=::----,/
,,..____,.
569
572
570
J ulian Date 1983- 1984+ 7. Dead
Percent crabs shed and crab mortality
for the protein skimmer stocked at h i gh
densit ies ( Ju 1y-August, 1984)
41
571
573
TABLES
42
TOTAL CRABS
IN SYSTEM
CRABS ADDED
TO SYSTEM
CRABS SHED
IN SYSTEM
DEAD CRABS
IN SYSTEM
-0.12904
-0.56517
0.39741
o. 10666
o. 11087
-0.21601
0.31999
0.5]113
Salinity
-0.31582
o. 14335
-0. 74350 ;~
0.01407
Dissolved Oxygen
-0.34044
0.18158
-0.45876
0.35894
PARAMETER
pH
-
Temperature
Dissolved Carbon Dioxide
0.75709*
0.28657
0.27222
0.50144
A1ka 1 in i ty
o. 17417
-0.50389
0.69399
-0.30473
Cal c ium
0.00933
0.58488
- 0.57670
0.20385
BOD
o. 17815
- 0.17718
-0.01302
-0.50861
-0.28728
0.15169
-0.41453
0.46299
~
w
% 02 Saturation
* Signifi c ant at the 0.05 level
Table 1.
Pearson correlation coefficients comparing c rab population variables with
physical and c hemical water quality parameters for the protein-skimmer
system stoc ked at high densities, days 557-574
TOTAL CRABS
IN SYSTEM
CRABS ADDED
TO SYSTEM
CRABS SHED
IN SYSTEM
DEAD CRABS
IN SYSTEM
Arrvnonium (NH4)
-0.09128
-0.21898
-0.09264
-0.26643
Ammonia (NH )
3
-0.13563
-0 .68851
0.22128
-0.09309
Nitrate (No )
3
-0.07879
0.26317
-0. 77176•'r
0.04501
Nitrite (N0 2 )
-0.32347
-0.49071
-0.21245
-0.23364
Marine Agar Plate Counts
0.60826
-0.05841
0.57525
-0.05280
MPN Col iforms
0.44623
0.29331
0.05411
-0.14074
MPN E. co li
0.45725
0.27240
0.01495
-0.15551
PARAMETER
.t.t-
---
*Si gnificant at the 0.05 level
Table 2.
Pearson co rrelation coeffi cients compa ring crab population variables with
nitrogen and microbiological quality parameters for the protein-skimmer
system stocked at high densities, days 557-574
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45
UPD 6407/8·86