FULL- SCALE OPERATIONAL DEMONSTRATION OF

FINE MESH SCREENS AT POWER PLANT INTAKES

V. Brueggemeyer, D. Cowdrick. and K. Durrell

Tampa El ectri c Company

O. Box 111

Tampa, Florida 33601

S. Mahadevan and D. Bruzek

Mote Marine Laboratory

1600 City Island Park

Sa rasota, Flori da 33577

ABSTRACT

Tampa Electric Company (TEC) operates four coal- fired generating units at the

Big Bend Station located on Tampa Bay in North Ruskin, Florida. All four units

use once- through condenser cool i ng systems.

Prior to the construction of Big Bend Unit 4, environmental agencies expressed

concern over entrai nment of organi sms. Engi neering and bi 01 ogi ca 1 studi es conducted in 1980 indicated that the application of fine mesh screens (FMS) at the

station would reduce entrainment levels.

As a result of this, the environmental agencies authorized the use of a oncethrough condenser cooling system in Unit 4 with the installation of FMS (0. 5 rom)

on both Uni ts 3 and 4.

In conducting required post-operational (February 1985) studies to verify expected

screening efficiencies, TEC identified that sampling methodologies. and the nature and extent of operational and maintenance procedures were critical in

achieving good screening efficiencies.

This paper summarizes TEC efforts in ascertaining adequate screening efficiencies.

INTRODUCTION

In February 1985. Tampa Electric Company (TEC) placed in commercial operation

Unit 4 at the Big Bend Station. The site presently operates a total of four

coal-fired generating units in the 400 MW range and is located on the eastern

shore of Tampa Bay in North Ruskin, Florida (Figures 1 and 2). All four units

have once- through condenser cool ing systems. Each uni t draws approximately

540 cfs of bay water from a single intake canal and releases it to the Bay via a

single discharge canal.

Both the Environmental Protection Agency (EPA). Region IV, and the Florida Department of Environmental Regulation (FDER) expressed concern, prior to the construction of Unit 41 over losses of organisms due to entrainment into the existing

condenser coollng systems. Accordingly. early in 1979 TEC conducted a full-scale
prototype evaluation of a fine mesh screen (FMS) system as part of Unit 4' s 316

Demonstration. The prototype studies were performed by Stone and Webster

Engineering Corporation (SWEC) and Mote Marine Laboratory (MML).

Based on the positive results obtained from the prototype. the environmental agencies determined that Unit 4 could be constructed with a once- through condenser

cool ing system provided that a FMS system be incorporated into the intake structures

of both Units 3 and 4. This novel system consists' of six continuously traveling

screens with 0. 5 mm screen mesh with specially designed organi sm troughs and spray

washes (Fi gures 3 and 4).

Verification of expected screening efficiencies was required by the environmental

agencies. Results from the post-operational biological studies identified that

not only was the sampling methodology not adequate. but also more crucially, there

were operational differences between the prototype and the full-scale system.

An intensive operational and maintenance (0 & M) auditing program was conducted.

Such a program enabled TEC to develop critical 0 & M procedures. All six screens

are now in optimum operational conditions.

With sampling methodology streamlined, TEC conducted additional biological studies

during the 1987 spawning season in order to verify expected screening efficiencies.

Thi s paper focuses on the i ntens i ve 0 & M audi ti ng program performed as a mean

to develop and implement critical 0 & M procedures; and furthermore, the subsequent

verification of screening efficiencies.

FULL- SCALE PROTOTYPE SYSTEM

In 1979. two separate studies were conducted. One was a partial backfit of an

existing traveling screen with 0. 5 mm FMS to determine whether Representative

Important Species (RIS) as shown on Table 1 were capable of surviving impingement

on the screens under conditions of existing screen design. The other was a flume

study in which RIS were impinged on a FMS panel over a range of impingement

velocities and durations to determine the relationship between specific velocity/

impingement duration conditions and survival rate. Both studies yielded positive results, with acceptable survival rates (1). Based on this, a decision

was made to proceed with a full-scale prototype investigation.

A full-scale prototype, identical in every way to the proposed installation except

only 0. 6 m wide, was constructed and placed into service in March 1980 (Figures

5 and 6).

The prototype was located in the intake canal upstream of the existing Units 1

through 3 travel ing screens and pumps (Figure 2). The screen was situated on

a test platform connected to land by an existing bridge.

Figure 5 shows a more detailed plan of the screen operating deck. The prototype

screen was of the dual- flow type and incorporated all of the features required

for fine mesh screening. Seal s were incorporated between screen baskets and between

the baskets and the side frames to minimize the passage of organisms through these

areas. The screening medium was a 0. 5 mm square mesh made of woven-monofilament

polyester, and each of the 48 screen baskets were 0. 6 m wide by 0. 6 m high.

The screen was capable of operation at speeds of up to 14 cm/s and maximum impingement durations of 7 minutes. Flow through the screen was supplied by an in- line

pump (bow thruster) located under the test platform and connected directly to the

screen via a transition section (Figure 6). Assorted pulleys allowed for flow
adjustments which resulted in screen velocities of 8 to 46 cm/s.

The test screen incorporated a shallow lifting bucket on ,each 0. 6 m wide screen

basket which retained approximately 2. 54 cm of water. A low pressure (10 psi)

spray header located on the ascendi ng si de of the screen acted to remove organi sms

from the screen mesh surface and lifting buckets. A high pressure (55 psi) spray

header was located on the descending side of the screen to remove any remaining

debris into a separate trough. A screenwash sump with a strainer was located

on the operating deck and took suction from the filtered water. As each screen

basket passed the spraywash. organisms on the mesh or in the lifting bucket were

gently rinsed into a collection trough (Figure 6). Once in the trough. the organisms flowed by gravity into a collection tank where organisms were collected and

transported to the aboratory for anal ys is.

The results of these studies concluded that the FMS technology was a viable alternative for removal of organisms from the circulating cooling water and that the

5 rom mesh used was capable of effectively screening RIS ife stages under study (1, 2). Furthermore, the studies also concluded that the installation of this

technology on Big Bend Units 3 and 4 would result in entrainment losses less than

those experi enced wi th Uni ts 1 through 3 wi thout di 1 ut ion pumpi ng (1).

In addition to the above studies, two other studies were conducted to gather information pertinent to the overall evaluation of FMS technology at Big Bend Station.

These studies indicated the following (1).

The spraywash system was less effective than anticipated and a substantial

degree of carryover to the high- pressure wash occurred.

A porti on of the organi sms encounteri ng the prototype screen were not

effectively screened; length data from organisms which had not been

screened suggested that ineffective sealing around the screen assembly

could be partially responsible for this.

On the basis of these results, TEC authorized SWEC to develop modifications.

Two modifications were made and incorporated to the system for further evaluation

during the Spring of 1981. One consisted of making the lifting buckets wider

and shallower. The other one consisted of installing new seals between individual

screen baskets to prevent organism ,losses through these areas. The rubber seals

were capped with stainless steel tensioning bars to hold the rubber firmly against

each adjacent screen basket. In addition. the screen s frame- to-basket seal, which

prevents losses between the stationary frame of the screen and the rotating baskets,

were al so inspected and adjusted to achieve better sealing.

Subsequent to these modifications, biological studies were conducted to determine

the effectiveness of these changes. The studies concluded that the improved design

features successfully eliminated the previous inefficiencies in the low- pressure

spraywash system; and that the replacement and adjustments of screen seals were

critical in obtaining high screening efficiencies () 80%) (1). Results of this

study are summarized in Table 2.

Based on this, the environmental agencies determined that Unit 4 could be constructed with a once-through condenser cool ing system and that a FMS system be

installed at the intake structures of both Units 3 and 4.

FINE MESH SCREEN SYSTEM

Figures 3 and 4 show the arrangement of the screenwell equipment for Units 3 and 4.

Six fine mesh (0. 5 mm) traveling screens. designed and fabricated by FMC Corpora-
tion, filter all water entering the screenwell. Standard, coarse mesh, dual flow

traveling screens filter the water before it enters the four circulating water

pumps. The coarse mesh screens are required to protect the pumps from debris in

the event that the emergency slide gates. in the sheet pile wall of the screenwell

opens upon high differential pressure.

Low pressure and high pressure screen wash pumps take suction from the circulating

water pump discharge and provide wash water to the spray nozzle supply headers

in each of the six fine mesh screens. Spray wash water with entrained organisms

and debris is collected in a trough and routed to an organism return sump. The

sump incorporates a trash basket to faci 1 i tate removal of debri 

Three 50% capacity organism return pumps take suction from the sump and discharge

into one of two 18 inch fiberglass organism return lines. The organism return

system discharges into a natural embayment south of the circulating water discharge

canal (Figure 2). The organism return pumps are Wemco- Hidrostal centrifugal screw

pumps operating at 375 RPM with clearances sufficient to pass a 5- inch spherical

object.

Stop logs are provided to close the entrance to the screenwell when a fine mesh

screen is removed for maintenance.

A control system has been provided to vary the speed of the fine mesh screens

from 7 to 28 fpm to minimize differential pressure across the screens. Screen

speed is varied by a General Electric variable frequency, variable voltage, motor

speed control system. Differential level is measured across the intake structure

with one of two bubbler type level probes.

POST-OPERATIONAL BIOLOGICAL STUDIES

In fulfillment of environmental permit requirements for the construction of

Big Bend Unit 4, TEC conducted post-operational studies during the 1985 spawning

season in the full-scale FMS system in order to verify the results obtained earlier

by the prototype system.

FMS Survivabilit Study

This study was conducted in order to verify that RIS were capable of surviving

impingement on the full-scale system once screened.

Sampling for this study was conducted during March through September 1985, at

three locations pertaining to Unit 4: (1) the screenwash station in front of

the screens after the organi sms were screened and washed to the screen return;

(2) the organism return discharge (ORD) station at the discharge point of screened

organisms in the northern embargement of Apollo Beach; and (3) the control station

at the intake canal in front of the intake screens. Station locations are shown

in Figure 2.

Methods used during this study were essentially similar to those used during the

FMS Prototype study.

Results from this study are summarized in Tables 3 and 4. The study concluded

that survival rates obtained were comparable to those obtained by the Prototype

study, and in some cases, they exceeded those of the Prototype study (4). 

addition, there was no significant difference in survival rates between stations;

however, minor differences can be attributed to natural mortal ity not associated

to the FMS (1).
,... ....., ..... .., .

FMS Entrai nment Stud

The FMS Entrainment study was conducted to evaluate and verify the screening efficiencies of the full-scale system.

Sampling was conducted at two stations simultaneously sampled. One station was

located at the intake canal, and the other was located at an access manhole behind

the screens (Figure 3). Samples were collected day and night using a 0. 505 mm

ichthyoplankton net. Four replicates were collected during each of the day and

night samplings. The intake samples were taken in oblique tows over the entire

water column. A volume of 100 cubic meters of water was filtered during each

intake replicate. The manholes samples were filtered through the net for a period

of twenty minutes over the entire water column. A flowmeter suspended inside the

mouth of the net determined the vol ume of water sampled.

As indicated by Table 5, the results of this study showed that organisms, particularly eggs and larvae, were being entrained.

SOLVING THE PROBLEM

As previously discussed, the testing of the FMS system during the 1985 spawning

season resulted in efficiencies much lower than expected. To address the problem,

TEC establ ished a task force to identify potential problem areas and seek their

resolution prior to considering any design changes. Past 0 & M practices were

reviewed, as well as, test methodology. In addition, necessary maintenance was

performed to get the FMS in as designed conditions. These activities resulted

in significant findings affecting screening efficiencies. Each of these are discussed below.

Maintenance

During post-operational testing of the FMS system, it was noted that frequently

one or more of the six screens were out of service due to mechanical problems

of the screen main chains. This caused higher flow rates through the screens,

as well as, higher approach velocities, both of which had been identified as effecting screening efficiencies during previous studies (1, I). In an effort to address

this, the screen chains underwent major repairs during the winter of 1986.

In order to determine the effectiveness of and optimum level of maintenance required

for the screens, an auditing program was instituted by the task force and performed

by MML. Weekly audits of the screens consisting of physical inspections of the

screens and the screen controls were performed. An audit form was developed and

used during the audit (Figure 7). The audits revealed the following problem items:

Tears and punctures of screens.

Tears of frame- to-frame seals.

Inadequate installation of and tears of chain- to-frame seals.

Clogging of spray nozzles and spray wash supply system.

All of the above items were found to be associated with biofouling of the system.

In light of the above, TEC had new seals installed and adjusted. In addition,

TEC implemented daily surveillance by operators, as well as, biweekly preventive

maintenance plans by maintenance crews.
d____--

Samp 1 i ng Methodology

In addition to the review of the 0 & M activities, TEC with the assistance of

MML reviewed the sampling locations and sample methodology. 

Divers inspected

the marine environment within the screenwell and determined that sampling at this

location would not be representative due to the establishment of fish populations

within the screenwell.

As a result of this finding, it was decided to add sample ports at the FMS assembly

outlets (behind the screen themsel ves). Sample ports were designed to be capable

of sampl ing at three preselected flow elevations to account for a representative

flow through the screens. Engineering 

tests verified this and sample ports were

installed in all six screens 

().

It was also determined that collection of inlet samples necessary for the calculat i on of sc reeni ng effi ci enci es shoul d be done di rectly in front of the screens

instead of using tows at the intake canal.

Due to the significant increase in sampling costs related to these changes if

sampling would take place at each of the six screens, TEC evaluated the viability

of sampl ing only one screen. Since the increased level of 0 & M practices assured

that one screen would be mechanically representative of the others; it only remained

necessary to assure that one screen would be hydraulically representative of the

others. In order to accomplish this effort, TEC contracted SWEC and Alder Research

Laboratories to conduct the necessary flow and velocity measurements.

Flow and velocity measurements were taken using an electromagnetic probe and meter.

Velocities were taken along the centerline of the FMS discharge opening into the

screenwell at 0. 6 m intervals over 3. 6 m of the opening. Horizontal velocity

profiles were also determined by taking measurements at 0.

3 m of the centerline.

Analysis of the data indicated that flow rates through all six screens were uniform

(). 

In addition, flow and velocities at the inlet and outlet of the 

sampling

points under consideration were determined to finalize the design of the new sample

ports.

On the basis of this study, sample ports at both the inlet and outlet of two screens

were installed. One screen was used for actual testing and the other one as backup.

FMS Bi ofoul i ng

Marine growth, particularly barnacles and oysters, was identified as the major

source of screen mesh and seal failures, and of spray line and nozzle clogging.

These organisms have a tendency to attach themselves to the larvae pan of the

FMS panels and puncture the screen mesh. 

Generally, these punctures are small

(pencil diameter or smaller); however, they are large enough to allow entrainment of organisms. In an effort to promptly identify screen failures, TEC has

implemented biweekly preventive maintenance inspections.

Barnacle growth on the screen frames was also found to contribute to failure and

poor performance of the frame- to-frame seals by causing them to deform and tear.

Gaps between frames allow the passage of organisms into the screenwell. 

In response to this, TEC implemented both operator surveillance and maintenance inspections with a two-man crew capable of replacing these seals in a short time.

Barnacles and oysters were found to lodge themselves in the piping system causing

spray pump performance to degrade rapidly. Although there is currently a duplex

strainer in the suction to the high pressure pumps and one in the suction of the

low pressure pumps, growth still occurs between the strainers and the pump suctions.
0 & M procedures institued by TEC have found necessary to disassemble and clean the

pumps as often as once a week. In an effort to minimize maintenance requirements,

TEC intends to replace the duplex strainer in the suction of the high pressure

pumps, where most of the clogging tends to occur, with individual strainers.

Pump discharge lines were also found to be susceptible to biofouling resulting

in a decrease of pressure available to the screen spray nozzles. Loose shells

tend to collect at elbows restricting pressure to the point that the lines must

be shut and cleared. This still remains a problem. Possible solutions being

considered are annual or biannual manual cleaning of the pumps during system outages, and modifications to the system to incorporate pipe line pigging capability.

Loose shells in the spray nozzles were also identified as the cause of improper

removal of screened organisms. Operator surveillance implemented by TEC is geared

to evaluate spray patterns and intensity. Spray nozzle headers are flushed manually requiring the shutdown of a screen for a short period of time only.

As discussed above, biofouling has been identified as a major source of maintenance

problems which greatly affects screening efficiencies. Control of it is very difficult. Chlorination of spray water would defeat the intent of the FMS. Toxin releasing paint applications have been practically banned by the environmental

agencies. Thus, TEC has opted to control it by mechanical means which are manpower

and cost intensive. One possible solution TEC is considering is the use of nontoxic, low surface energy paints on critical FMS components (e.g. screen frames and troughs). Testing of these paints as to their viability in such a system is being

eva 1 uated by TEC.

FMS OPTIMIZATION STUDY

As already described, the post-operational FMS Efficiency study and the 0 & M

auditing program indicated that 0 & M procedures, as well as, sampling methodology

were not adequate to determine accurate screening efficiencies.

With screens in optimum operation condition and sampling methodology streamlined,

TEC requested in March 1987 approval from both EPA and FDER to conduct a FMS Optimization study during the 1987 spawning season to verify screening efficiencies.

Sampling was conducted from both the intake canal (boat) and the fine mesh screen

platform (Figure 3). Six replicate pump samples were collected from behind screen

3A (designated as B- 3A), along with six replicate pump samples from in front of

both sides of screen 3A (designated as 3A-West and 3A-East). Previous engineering

flow studies determined that the flow of water was approximately equal across

all six screens; therefore, screen 3A was designated to provide representative

information that can be applied to all six screens. In addition, three replicate

pump samples were collected from behind each of the remaining five screens as

back-up samples in the event sampl ing appeared inadequate at screen 3A. Pumps

were run for 30 minutes and sampled three water levels (surface, middle, and bottom)

10 minutes at each level. The flows from each pump were channeled into the intake

screenwell located behind the screens, where the water from each screen location

was pumped into a corresponding 0. 505 mm ichthyoplankton net. A series of oblique

tows (six replicates) was also collected in the intake canal by boat during each

set of samples.

Each sampling event consisted of two day samplings (morning and afternoon) and

one night sampling. Screening efficiencies were calculated by dividing the values

from the B- 3A sample by the mean of the 3A- West and 3A-East samples. This provides the percentage of organisms which were able to pass through screen 3A. Multiplying this number by 100 then subtracting 100 provides screening efficiency. Screening
efficiencies were calculated for each identified species, as well as for total

species at various life stages (eggs, prolarvae, etc.

Resul ts presented here represent the ana lys i s first three months (March - June) of the 1987

mean densities of eggs, larvae (prolarvae and

lected over the four sampling dates indicated

bers of organi sms observed.

of samples collected for the

spawning season. Analysis of

postlarvae), and invertebrates colan overall, strong increase in numTable 6 presents the summarized results for both the RIS and other species collected in relatively high abundances. 

As results indicate, screening efficiencies averaged va 1 ues in excess of the expected 80% previ 

study; with eggs averaging 95%, larvae 85. ous 1 y concluded by the Prototype

5%, and invertebrates 100% (1, ~).

SUMMARY AND CONCLUSIONS

As the data indicate, adequate sampling method and more importantly the implementation of adequate 0 & M procedures are critical to assuring good screening efficien- cies. Because of environmental concerns, TEC has implemented 0 & M procedures

primarily targeted to the manual control of biofouling, which is considered the

source of much of the FMS maintenance problems. 

Design modifications, as well as, the use- of non-toxic, low surface energy paints are being considered by TEC

as ways of optimizing 0 & M procedures to reduce costs.

The present level of 0 & M procedures has not required the addition of new operators or maintenance personnel. Costs 

associated with the repai r of seal s have been estimated to be in the range of $75, screens and

wide range is due to the uncertainty which 000 - $150, 000 per year. The still exists regarding the use of non- lubricated chains. Even though the initial set developed problems during a short time frame, the present replacements may last longer.

In summary, the Big Bend Station FMS system is effectively screening RIS organisms

and life stages.

REFERENCES

Tampa Electric Company. " 316(a) and (b) Demonstration, Big Bend Station

- Unit 4. " prepared by Stone and Webster Engineering Corporation,

August 1980.

Tampa Electric Company. " 316(a) and (b) Demonstration, Big Bend Station

Unit, Fine Mesh Screen Study Report.

" prepared by Stone and Webster Engineering Corporation, November 1980.

Stone and Webster Engineering Corporation. "Supplemental Engineering Report Based on the 1980 Fine Mesh Screen Optimization Study, Big

Bend Unit 4, Tampa Electric Company.

" May 1981.

Tampa Electric Company. " Fine Mesh Screen Survivability Study Big Bend Unit 4. " prepared by t4ote Marine Laboratory, December 1986.

Stone and Webster Engineering Corporation. "

Fine Mesh Screening Flow Measurements, Big Bend Station - Units 3 and 4.

" February 1987.

Tampa Electric Company. " Fine Mesh Screen Optimization Study.

by Mote Marine Laboratory, July " prepared 1986.
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Operational Audit Form
Table 1

REPRESENTATIVE IMPORTANT SPECIES (RIS)

AT TAMPA ELECTRIC COMPANY

BIG BEND STATION (1)

Common Name Scientific Name

Bay anchovy

Black drum

Silver perch

Spotted seatrout

Scaled sardine

Tidewater siJverside

Stone crab

Pink shrimp

Ar;Jeri can oyster

B1 ue crab

Anchoa mi tchi 11 i

Pogonias cromi s

Bairdiella chrysoura

Cynoscion nebulosus

Harengula jaguana

1'1enidia beryl1ina

Men'i ppe mercena ri a

Penaeus duora rum

Crassostrea vi rgi ni ca

Cal1inectes sapidus

Table 2

TEST RESULTS

SPRAYWASH EFFICIENCY SAMPLING

1981 OPTIMIZATION STUDY (l)

Tota 1 Number of Range of ~1ean

Soeci es Name Life Stage Organ isms % Lass % Loss

Anchaa mitch i 11 i Egg 5238 3 - 1.5

Bairdiella chrysura Egg 1780 0 - 14.

Cynasci on nebulosus Egg 100. 0 - 100. 100.

Cynosci an spp. Egg 114 0 -

Sciaenidae unid. Egg 1828 1 - 30.

Anchoa mi tchi 11 i Pra1arvae 1007 0 - 24. 1.7

Sciaenidae unid. Prolarvae 0 -

Anchoa mitchi 11 i Pastl arvae 847 0 - 22. 1. 7

Bairdiella chrysura Postl arvae 0 - 40.

Cynosci on nebulosus Postlarvae 0 - 100. 20.

Pogonias cromis Pastlarvae 0 -

Sciaenidae unid. Postlarvae 0 -

Mem ppe mercena ri a Juvenil e 0 -

Shrimp unid. Unidentified 498 5 - 1.4

Brachyura unid. Un staged zoea 2854 3 -

Menippe mercenarJa Ioeal stage 171 0 - 60. 1.8

Men i ppe mercena ri a Ioeal stage 2 0 -
Table 3

COMPARISON OF INITIAL SURVIVAL 

(%)

DURING THE PROTOTYPE AND FMS

SURVIVABILITY STUDIES (i)

Taxa Prototype Study FMS Survi vabiJ i ty Study

Screenwash Screenwash ORa Contra 1

Fish Eggs:

Anchoa mi tchi 11 i

Sci aeni dae

Fi sh Larvae:

Anchoa mi tchi 11 i

Sciaenidae

Invertebrates:

Ca ri dea

Xan th i dae

Pi nnotheri dae 100

Table 4

COMPARISON OF FISH EGG HATCHABILITY AND

LATENT 48 HOUR SURVIVAL 

(%) 

DURING THE

PROTOTYPE AND FMS SURVIVABILITY STUDIES (i)

Hatchabilit

Taxa Prototype Study H1S Survi vabiJ ity Study

Screenwash Screenwash ORD

Fish Eggs:

Anchoa mitchilli

Sci aeni dae

Latent 48-Hour Survival

Fish Larvae:

Anchoa mitchi 11 i

Sci aenidae

Invertebra tes:

Caridea

Xanthi dae

Pinnotheridae
Table 5

TEST RESULTS

1985 FMS EFFICIENCY STUDY

t1ean Densi ty Mean Den s i ty Range Mean

li fe Stage Inta ke Manhole % Loss % Loss

Fi sh Eggs 12184. 9545. 55- 100 78.

Fi sh Larvae 177. 166. 100 94.

Invertebrates 203. 29. 100 14.

Table 6

SUMMARY DATA FOR RIS AND OTHER SPECIES

FOUND IN RELATIVELY HIGH ABUNDANCES

COLLECTED FROM FOUR ANALYZED SAMPLING PERIODS 

()

Mean Density Mean Density

Sped es L He (fl00m (fl00m Range of 14ean

Stage Front Behind % Loss % Loss

Sdaenidae spp. Egg 38595 1062 0- 44.

Anchoa mitchilli Egg 12860 1071 0- 52.

Anchoa mi tchi 11 i La rvae 239. 26. 0- 33. 11.

Bairdiella chrysoura Larvae

Cynoscion nebulosus Larvae 1.1

1enippe mercenaria Zoea 24. 1.2

Penaeus spp. Juven il e 1. 9

Blenniidae spp. Larvae 29. 0- 76. 17.

Gobiidae spp. Larvae 30. 5- 58. 25.

Gobiesox strumosus La rvae 1.1 100 11.2