Gulf and Caribbean Research
Volume 7 Issue 4
January 1984
Growth and Production of the Dwarf Surf Clam Mulinia lateralis (Say 1822) in a Georgia Estuary
Randal L. Walker Skidaway Institute of Oceanography
Kenneth R. Tenore Skidaway Institute of Oceanography
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Recommended Citation Walker, R. L. and K. R. Tenore. 1984. Growth and Production of the Dwarf Surf Clam Mulinia lateralis (Say 1822) in a Georgia Estuary. Gulf Research Reports 7 (4): 357-363. Retrieved from https://aquila.usm.edu/gcr/vol7/iss4/7 DOI: https://doi.org/10.18785/grr.0704.07
This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. Gulf Research Reports, Vo1. 7, No. 4,357 -363,1984
GROWTH AND PRODUCTION OF THE DWARF SURF CLAM MaLrNrA LATERALIS (SAY 1822) IN A GEORGIA ESTUARY
RANDAL L. WALKER AND KENNETH R. TENORE Skidaway Institute of Oceanography, Savannah, Georgia 31416-0687
ABSTRACT The bivalve Mulinia lateralis is a dominant member of estuarine benthos, but its presence and abundance in Georgia estuarine waters is sporadic over time. Recruitment and production was monitored fuom 1977 through 1981 at three inner and one outer more saline ( ) 18 ppt) areas of Wassaw Sound. Until the winter of 1981, Mulinia lateralis was absent or at very low densities. Significant settlement occurred in January 1981 when densities in the outer sound reached as high as 63,000 individuals . m-2 , The clam was more abundant in sandy mud (x = 10,161 ' m-2 ) than mud (i=271 .m-2) orsand (T=263.m-2).Cohortproductionvariedfrom0.3gdrywt.m-2.4 months-l intheinner sound to 325 e dry wt . m-2 .7 months-l in the outer Sound, with the mean biomass ranging from 0.6 to 513 g dry wt . m -2, respectively. When present, Mulinia lateralis contributes significantly to benthic production available to com- mercially valuable fish and crabs. That this food resource is annually and seasonally episodic could contribute to year-to- year fluctuations in production of species preying on benthos.
INTR6DUCTI6N winter to 30oC and 30 ppt in the summer. Sediments range and mud The dwarf surf clam Mulinia lateralis (Say lS22) (Bi- from silt-clay to fine sand with interbedded sand valvia; Mactridae) is a typical dominant member of estuarine the most prevalent (Howard and Frey 1975). benthos whose density characteristically fluctuates widely. MATERIALS AND METHoDS Populations of this clam may dominate the benthos one year or part of a year, only to be absent the following year(s). Four stations (Fig. 1) were sampled monthly from Janu- Fluctuationsintheabundanceofbenthosofwassawsound, ary to December 1981 by taking six 0.05-m2 van Veen in Georgia (Fig. 1),may be inpart caused by salinity depres- grabs at each station. Samples were sieved through a sions in winter/spring when many benthic species spawn 0.297 -mm mesh and preserved in lO% formalin in sea (Walker et al. 1980,Walker and Tenore 1984). For example, water. Samples were returned to the laboratory, sorted M. lateralis and the northern hard clarnMercenaria mercen- under a dissecting scope and specimens of M. lateralis were aria (Lnft) did not settle significantly between 1977 and counted and measured for shell length (longest possible 1980, when low winter salinities resulted from heavy rain- measurement, i.e., anterior-postedor distance). fall in upstate Georgia. Becauseof adroughtin l98l,salin- Station I was located in the Skidaway River approxi- ities were not depressed in winter/spring and a significant mately I mile south of the Skidaway Institute of Ocean- set of juveniles of M. mercenaria andM. lateralis occurred. ography where the clams occurred in a muddy substrate in The contribulion of M. lateralis to benthic production is approximately 1.5 m of water at mean low water. Station 2 especially important because this species, when present, is was located in the Wilmington River at the U.S. 80 draw- an important source of food for many commercially valu- bridge at Thunderbolt, Ga., where the clams occurred in a able fish and crabs (Brever 1957, Tagatz 1969, Virnstein muddy substrate in approximately 0.5 m of water at mean t977). Little information exists on the production of op- low water. Station 3 was located at the junction of Skid- portunistic species such asM. lateralis.We describe here the away and Wilmington rivers, where the clams occurred in a productionof asinglecohortage-class of M. lateralisfollow- sandy mud substrate in approximately 2 m of water at ing the 1981 set of thisbivalve after severalyears of recruit- mean low water. Station 4 was located in the Wilmington ment failure. Information was gained on the contribution River near the junction of Wilmington and Cabbage islands, of the clam to benthic production during a period of high where the clams occurred in approximately 0.2 m of water clam density. at mean low water. sruDysrrE u.,lli,,i$" |:i';i ff,,i;i,:[;,\_"58,Y',;T:1.':,xfJJl: Wassaw Sound (Fig. l) is a coastal estuarine embayment measured to the nearest mm, the flesh was removed and located in the Georgia Bight (Howard and Frey 1980). Semi- dried to constant dry weight at 80oC for 48 h. diurnal tides average 2.4 m, with spring tides ranging ap- Secondary production was calculated using the instan- proximately 3.4 m (Hubbard et al. 1979).Water tempera- taneous growth model of Waters and Crawford (1973): tures (Ddrjes 1972) and. salinities at themouthof the Sound (Howard and Frey 1980) range from 8oC and 20 ppt in the P = GB
Manuscript received April 23, 1 9 84 ; accepted May 1 4,1 9 84 where P = production in grams 'm-2, G = instantaneous
357 3s8 WALKER AND TENORE
StudfArea
320
M ,0 0) q g .) q a M E os :) '2, 5/M o --' Sla 4 s/M
% Yrrzs\. Wassarv Sound Sampling lor Mulinia lateralis ( m-z) orn t)' to'ooo Osr, a >looo O 'loo 012 /6- L--r-l-r-J o'lo kilometers eoo
refer to Figure l. The distribution and relatiye abundance of Mulinia loterolis in Wassaw Sound, Georgia. Letters below the density-symbols substrate type: sh = shell, cs = coarse sand, s = sand, s/m = sandY mud, and m = mud.
to a growth for the time interval, and B = mean standing crop found throughout the Sound. Clams set intertidally outer Sound (up between giventime intervals (B= [Bt + Bt+r ]/2). Instantan- depth of 7 m, with heaviest settings in the eous growth rate (G) is calculated as ln(W/Wo) where o to 63p00'm-2). Inshore of Skidaway and Wilmington and t represent the beginning and end of each time interval. islands, densities were ( 2000 ' m-2 . Densities also varied Annual production is equal to the summation of the indivi- with sediment type (Fig. 1). Clams had average densities of dual intervals' production estimates. Individual weights for 10,161 r.19,475 (SD)' m-2 in sandy mud, 277 !522 the table were obtained by taking the mean of the clam (SD)' m-'? in mud, 263!468 (SD)'m-2 in sand, and lengths per month per station and applying that value to were absent in coarse sand and shelly bottoms. In areas were the shell-length to dry-weight regression equation. where the substrate changed from sand to mud, clams Growth was determined by plotting the mean weight of more dense in the sand-to-mud interphase. to the clams against time. Mean weights were determined using Densities increased at the four stations from January monttrly mean shell lengths and converting to biomass. February and then declined. Some specimens ofM' lateralis in Wassaw Sound were mature and ripe in April but there RESULTS was no new recruitment. None were found at Sta 1,2, and 4 August (Fig'2)' Clams were absent or at low densities (( 10 ' m-2 ) from 3 after April. Clams persisted atsta until m-2 at Sta 2 to 1977 to winter 1981. In January 1981 newly set clams were Densities varied greatly from a low of 525 ' GRowru AND PRoDUCTToN oF THE DwaRp SuRp Crapr 3s9
SURVIVORSHIP CURVES OF MULINIA LATERALIS The regression equation of shell length (SL) in cm to mean dry weight (DW) in grams is: . . . Station 1 y=2.1t+0.04X-0.00036S8X2 |.2=O.ggO ^ ^ Station 2 y = 2.q8+ 0.02X-0.00031+sX2 r2= 0.980 ! r Station 3 y = t.O7 +0.05X-0.0004635X2 r2= g.93g I DW = 0.01095 (SL cm)2'e6E ,12 = 0.94 . . Station 4 y =3.82 + 0.03X-0.0001883X2 r2= 0.840
N and compares well to other bivalves (Winberg 1 97 I ). Changes E '4 in biomass with time were examined by the equation: OQE O fr=atb o o a where fr = mean dry weight and t = time in days from settle- E :1 ment at each of the stations. The estimate of initial settle- o o ment was the beginning of January. By using monthly data -o points, the prediction was made by varying the day of settle- 0 20 40 60 80 100 120 140 160 180 200 220 240 ment until the highest correlation coefficient was obtained. Days ('day I is tJanuary 1981) The best lrt (r2 = 0.99) was obtained when I or 2Jarwary Figure 2. Survivorship curves for Mulinia lateralis at Stations was used as the day of initial settlement. through 4. Day one is I January 1981. Exponential growth rates were highest at Sta 3 and low- est at Sta 4 (Fig. 4). Slow individual growth rates at Sta 4 . a high of 63,168 m-2 at Sta 4 in February. From January probably resulted from the high clam densities at that sta- to March, individuals declined from 63,168 to 17,346. m-2 tion. at Sta 4;similar declines occurred at the other stations from Cohort production, standing crop, and cohort turnover February to April. ratios varied from a high production value of 325 g DW . Histograms . . show changes in clam size with time and m-2 7 mo-l with a high standing crop of 513.44 C DW because there was only a single set, cohoft production at the m-2 at Sta 4 to a low production value of 0.29 g DW . m-2 four stations could be estimated (Fig. 3). . 4 mo-1 and low standing crop of 0.60 gDW. m-2 at Sta2.
Mulinia lateralis population:STATION 4
90 26 January tgBl 1 80 24 February 198 25 March 1981 6 May 1981 70 x=s5,965t'26,560(SD) m-2 t =63,168 132,529(SD) m-2 x=1 7,346.18589(SD) m-2 ,,= 17.7 124L4g56(SD) m-2 x= 0.29JO.O8(SD) cm x=0.50t0.12(sD) cm i=0.67+ 0.09(sD) cm 60 i=0.801o.09(SO) cm
o30840 B;; to .b, ao , o?i 'oo'a"F 1b os 6o qh,lo"6lo r? oo'rb ,fn*.)'sr or?oeojo.l"...F o,o0'orJ'or"6 '.s",'. .f1 o"o/o) r ro ro roro_ ro,rc \o to \o.ro \o (l)o oofodc60lq) ooo ro.o''roro .o \o) .o\o ro \o\o\o\o, \o \o )-rs .o n9 ..t|1,$..i";b" o -o _o oor;5o8olb.lo O o6.^b" \r '^b oYsP,^6 P-rb'-1b ooo(P.1 .f (E (I) 23 May 1981 t 30 June 1981 22 July 198 1 24 August 1981 7Or r=1 1,424i3875(SD) m-2 x=6153t3738(SD) m-2 x=1A22+47zlSD) m-2 i=OtO m-2 .] t=o.9810.1 1(SD) cm i=1.1310.'l 1(SD) cm i=1.2810.1 1(SD) cm i=O ^ouo] 40 1 30 1 ,o) ,o ] OJ ;b q? oro r.b oo n9 qo tb b- \- ( o'.'oloor\f.u5.t\r6 o o o \'\j\'\' ooo'\\'\'\'tf b" {'s".L' ao'ao to- \o \o \o \o \o \o \o \o \o \o \o \o \o \o \o O" od)bo^boof60 o-q!orsrboo o.,(1roof,'"t".t"$.*" oso\.\'\' a o'o'\' \'f6a^b \r\.
Shell Length (cm)
Figure 3. Monthly histograms for Station 4 showing changes in number . m-2, average size, and the formation of only one cohort. WALKER AND TENORE 350 TABLE I lateralis cohort Growth Curves for Mulinia production by instantaneous gtowth method' Cohod of ratio, mean density of clams for duration '395 r2 .9998 tutnover- for Station #'1 v = 41.3X = poput"tion, and the duration of the population ' 'Stations.l is in u Sg. laY'692 12= .9620 through 4' Cohort production Station #2 = the grams dry *"*:il,if"T.duration of v 32.60X'513 rZ = .9642 Station #3 = 2'- Station #4 Y = a5.5gY'472 r .gggs . Cohort* Cohort* Mean* Duration of Production P/B Monthly Population DensitY (r sD)
1431 !304 January to March Station 1 7.29 2.38 JanuarY to APdl Station 2 0.29 1.93 t48+252.6 462!517 JanuarY to APril Station 3 4.12 2.05 JanuarY to JulY Station 4 325.28 4.44 24,',|',|0!24,540 *Basedonlessthanoneyeaf'i'e.,3moforStal,4moforSta2 a and 3, and 7 mo for Sta 4' (6 #2 1o 27 ppt' survival and growth is optimum at2O '5 o --Th; is distribution of animals within estuarine systems #3 g.r;-rily ;;i;;ed to salinitv (Wells 1961' Iv.lenz.el 1964' Wass with salinity i gos). i)ther environmenial' factors associated for the lack of reductions, however, could be responsible Georgia' For annual recruitment of M' lateralis in ,r"..rrfut in i;;;;., with heavy freshwater runoff' a major shift as ;;;;; ;tt could affect larval transport and settlement Furthermore' heavy ;;[ changes in primary production' runoffcouldincreasetheamountofsuspendedsediments"t Davis (1960) showed that as well as alter bottom sediments' eggs and survival of clam (Mercenaria mercenaria) 510152025 ;;";rh of inJ ru*u. was correlated to the type and concentration of the bottom sur- Meat Img 'drY weightJ ,urious suspended material' Instability of suspension face can result in clogged filtering structures at Stations 1 through 4' settling Figure 4. Growth rutes for Mulinia lateralis i;;;;, burying newly-settled larvae or discouraging (Rhoads and Young 1970)' g m-2 3 fledingbivalves Cohort production was estimate d at 7 '3 DW ' ' at Sta 4' "i*tp.tti""ioiut cohort production was 100 times greater mc1 wiih a standing crop of 9'19 gDW'm-2 an'd4'l2g than in the more saline region of the outer Sound' . standing crop of 8'05 g DW' located OW. *-' '4mo-1 *ittt inner Sound' Further' Sta 1 and 3 were turnover rates (P/B) u, S,o t and 3 in the m-2 atsta 1 and 3, respectively' Cohort productive than Sta 2 4'40 for 24 and 14 times, respectively, more ranged from a low of t.93 for Sta 2 to a higlr of and 2'05' res- locatedintheareaoflowestsalinity.Thisresultedfrom Sta-4 with Sta I and 3 having ratios of 2'38 populations' Clams to Oenrlty and duration of the various pectively. The differences in estimates were attributed while those at "ia.n 4 were dense and survived for 7 mo' in clams. The higher the densities' the at Sta iiff.rence, i, densities and survived 4 mo' and turnover ratio Sta 2 had a low density higher the production, standing crop, decimated fo1- Poputation s of M. lateralis were quickly (Table 1). probably re- lowing a heavy set in January 1981' Mortality crabs Callinectes sapidus DISCUSSION r"f,tJ from predation by blue fragments abundance at all stations of shell benthic populations (Wells Rathbun. An Salinity is a major regulator of (MacKenzie 1977) suggested in, charucteristic of crab predation year-to'year excessive salinity depression adults 1961) and by the blue crab, a major predator of annual recruitment of fr.""V ptta"tion winter/spring appears to regulate the of M'lateralis also ppt) oc- of li. lateralis (Virnstein 1977)'Mortality in Wassaw Sound' Low salinity (( 20 (Say) as M. lateialis from the moon snail Po linices duplicarus from L977 to 1980' during the resulted curred during the winters of bore hole (Carriker 1951)' accounted could affect gamete determined by type p.rioa of no'rmal reproduction which losses at Sta 4' Mean ' for a smal1 percentage of the monthly development and survival' Larval development of and larval caused by snails were: 0' 504'23I'and 22 to 30 ppt clam mortalities M. lateralis is most successful e nVd from '5 March' April' and May' Larval tffi-;il;' m2 in February, but can occur as low as 15 ppt (Calabrese 1969)' GRowrH AND PRoDUCTToN oF THE DWARF SuRr Cr,q,lr 36r
TABLE 2
Annual production and P/B ratios of species of bivalves (production in g Ash Free Dry Weight m-2 unless otherwise stated). Bivalve age is in years.
Production PIB Max, Age Locality Reference Species g AFDW 1-2 y1-1 (yrs.) * Geukensia demlssas (Dillwyn) 3.34 2 0.28 Georgia, U.S.A. Keunzler 1961 Tagelus divisus (Spengler) 21.0 g DW 1.78 2 Biscayne Bay, FL Fraser 1 967 Tellina martinicezsls (Orbigny) 0.23 g DW 2.40 2 Biscayne Bay, FL Penzias 1969 Chio ne ca nc ellata (Linn€) 8.90 g DW 0.42 7 Biscayne Bay, FL Moore & Lopez 7969 Dosinia elegans (Comad) 0.13 g DW 1.25 2 Biscayne Bay, FL Moore & Lopez 1,970 Anodontia alba (Lnk) 14.09 g DW 1.43 ? Biscayne Bay, FL Moore & Lopez 7972 Mya arenaria (Linn6) 11.60 g DW 2.54 J Petpeswich Inlet, Can. Burke & Mann 1974 Mya arenaria (Linnd) 2.66 0.5 8 Lynher Estuary, U.K. Warwick & Price 1975 Scrobicularia phna (da Costa) 0.48 0.20 9 Lynher Estuary, U,K. Warwick & Price 1975 Macoma balthica (Linn6) 0.31 0.90 6 Lynher Estuary, U.K. Warwick & Price 1975 Macoma balthica (Linn6) 1.93 g DW 1.53 3 Petpeswich Inlet, Can. Burke & Mann 1974 Macoma balthica (Linnd) 3.40 1.93 8.10 Grevelingen Estuary, Neth erlands Wolff & deWolf 1977 Macoma balthica (Linnd) 0.94 1.00 8.r 0 Grevelingen Estuary, Netherlands Wolff & deWolf 1977 Ensis siliqua (Linnd) 1.37 0.2'1 10 Carmarthen Bay, South Wales Warwick et al. 1978 C era s t o de rma edu le (Linnd ) 0.21 0.2A 7 Lynher Estuary, U.K. Warwick & Price 1975 C era s t od erma edule (Linn6 ) 29 .25 1.59 5 Southampton Waters, U.K. Hibbert 1976 C era s t o derma edule (Lnn6 ) 71.36 1 .1 0 Southampton Waters, U.K. Hibbert 1976 C e ra s t o d erma ed ule (Lnnd) 46.44 2.61 5 Southampton Waters, U.K. Hibbert 1976 * * Cera st o derma edule (Ltnn6) 10.21 0.69 3.5 Grevelingen Estuary, Netherlands Wolff & deWolf 1977 * * C era st o d erma e dule (Lnn6,) 119.82 2.s9 3.5 Grevelingen Estuary, Netherlands Wolff & deWolf 1977 * * C e ra st o de rma ed u le (Lnn€) s1.76 1.13 3.s Grevelingen Estuary, Netherlands Wolff & deWolf 1977 Venerupis aurea (Gmelin) 0.70 1.1 1 5 Southampton Waters, U.K. Hibbert 1976 Venerupis aurea (Gmelin) 1,.25 1.10 5 Southampton Waters, U.K. Hibbert 1976 Venerupis de cussata (Linnd) 0.21 0.52 ? Southampton Waters, U.K. Hibbert 1976 V en erupis de cussa ta (Linnd ) 0.60 0.28 ? Southampton Waters, U.K. Hibbert 1976 Donax vittatus (da Costa) 0.72 2.10 2.5 Carmarthen Bay, South Wales Warwick et al. 1978 Venus striatula (da Costa) 0.62 0.41 10 Carmarthen Bay, South Wales Warwick et al. 1978 Tellina fobula (Gmelin) 0.29 0.90 6 Carmarthen Bay, South Wales Warwick et at. 1978 Tellina deltoides 2.35 1.42 4 Westernport Bay, Australia Robertson 1979 Abra alba (Wood) 1.45 2.0 1.2 Concarneau Bay, France Glemarec and Menesquen 1980 Cra s so strea v ir ginica (Gmetin) 4132Kca1 2.01 2 South Carolina, U.S.A. Dame 7976 My t ilu s e d uli s (Linn6,) 3.58 1.00 1 Southampton Waters, U.K. Hibbert 1976 Mytilus edulis (Linnd) 4.82 1.00 ? Southampton Waters, U.K. Hibbert 1976 Mytilus edulis (Linn6) 29.43 KJ Y-t ? 7 Lynher Estuary, U.K. Bayne & Worrall 1980 M)t tilu s e d uli s (Linn€ ) 14.40 KJ Y-t 2 7 Cattewater Estuary, U.K. Bayne & Worrall 1980 Mttilus edulis (Linn6) 790.0 ? I Nyckelbyviken Bay, Sweden Loo & Rosenburg 1983 Myrilus edulis (Lnn6,) 648.0 2 1 Nyckelbyviken Bay, Sweden Loo & Rosenburg 1983 Mytilus edulis (Lnn6) 47 6.0 2 1 Nyckelbyviken Bay, Sweden Loo & Rosenburg 1983 Mulinia la t eralis (Say) 7.29 DW 2.38 0.25 Georgia,.U.S.A. This study M ulinia la t era li s (S ay ) 0.29 DW r.93 0.33 Georgia, U.S.A. This study Mulin ia la t e rali s (Say) 4.t2DW 2.05 0.33 Georgia, U.S.A. This study Mulinia kteralis (Say) 32s.28 DW 4.44 0.58 Georgia, U.S.A. This study Me rc enarin merc ena ria (Linnd ) 62.82 3.02 Georgia, U.S.A. Walker 1984 Mercenoria mercenaria (Linn6) 23.71 1.85 Georgia, U.S.A. Walker 1984 M erc enaria merc enar ia (Linnd) 1 3 3.60 3.38 Georgia, U.S.A. Walker 1984 M ercenaria mercena ria (Linn6) 0.s 1 0.25 9 Georgia, U.S.A. Walker 1984 M e rc e naria merce n a r ia (Linn61 6.15 0.18 34 Georgia, U.S.A. Walker 1984 M erc e nar io mer cenar ia (tinnd ) 18.53 0.11 30 Georgia, U.S.A. Walker 1984 Mercenaria mercenaria (Linnd) 0.24 0.25 9 Georgia, U.S.A. Walker 1984 M er c enarin m ercenaria (Linn6) 6.57 0.19 34 Georgia, U.S.A. Walker 1984 M erc enaria m erc enaria (Linnd ) 6.49 0.22 30 Georgia, U.S.A. Walker 1984 M e rc e na ria mercena r ia lLinndl 3.99 0.52 8 Southampton Waters, U.K. Hlbbert 197 6 Merc enaria m erc enaria (Linn6 ) 14.00 0.28 8 Southampton Waters, U.K. Hibbert 1976 Mercenaria mercenaria (Linnd) 6.19 0.17 9 Southampton Waters, U.K. Hibbert 1976
* Given as Modiolus demissus in Keunzler (1961). ** Given as Cardium edule in Wolff and deWolf (1977). WALKER AND TENORE 362 in Wassaw Sound, however' than those TABLE 3 considerably higher bivalr.s because the population studied was production (values ciieO fo, oih., Some literature values for annual individuals' Turnoler ratios de- of marine communities' .o*ptitta ody of young in g Ash Free Dry Weight) 1975' .r.ur.O with increase in age of organisms (Nichols 1980, Walker 1984)' The short-term production Production Wu*itt the 3 to 7 mo that M' lateralis was g n1'2 Source ,uir, ir., the iate for LocalitY AFDW ' ' Y1-r Thus' ;;t;r;, was higher than reported for other bivalves' 8.0 to Sanders 1956 lateralis effectively Long Island Sountl, U.S.A. 64'5 at least' for a short period of tkne,M' 13'3 Warwick & Price 19?5 be a signifi- Lyniler Estuary, U.K. available food resources and in turn can Waters, U.K. 2203 Hibbert 1975 ila* Southampton .untrour.roffoodforpredators;however'year-to'year Grevelingen EstuarY, from recruitment fail- Netherlands 0.1 to 219'9 Wolff & dewolf 1977 variations in production that resulted also caused a Carmarthen BaY, ure that were carrsed by low winter salinities Warwick et al' 1978 to pre- South Wales 25.8 signitcunt instability in the availability of this clam respectively. These values represented 0, 1'1,1l,and16% dators. xanthurus of total mortality. The spot Leiostomus ACKNOWLEDGMENTS is also a major predator of M' lateralis (Virnstein LacepEde Drs' E' Chin and D' Menzel feeding primarily on The authors wish to thank lg77); those caught in June had been given to reviewing the manuscript' Special thanks are M. tateralis (personal observations). for and S. Mclntosh for the graphics and to estimates of M. lateralli ranged from 0'3 g Us. ,q,. noyette Production The work was supported 1 1 and are com- i. Lura foi typing the manuscript' DW. m-2 '4 mo to 325 gDW'm-2 '7mo number Georgia 5ea Grant Program under grant parable to production data for other bivalves (Table 2) and il;, usDL-RF/83 1 0-2 1 -RR1 o0- I 02. Lenthic communities (Table 3). Cohort turnover ratios were
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