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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 commercially valuable fish and crabs. That this food resource is annually and seasonally episodic could contribute to year-toyear fluctuations in production of species preying on benthos. INTR6DUCTI6N winter to 30oC and 30 ppt in the summer. Sediments range The dwarf surf clam Mulinia lateralis (Say lS22) (Bifrom silt-clay to fine sand with interbedded sand and mud valvia; Mactridae) is a typical dominant member of estuarine the most prevalent (Howard and Frey 1975). benthos whose density characteristically fluctuates widely. Populations of this clam may dominate the benthos one year MATERIALS AND METHoDS or part of a year, only to be absent the following year(s). Four stations (Fig. 1) were sampled monthly from JanuFluctuationsintheabundanceofbenthosofwassawsound, ary to December 1981 by taking six 0.05-m2 van Veen in Georgia (Fig. 1),may be inpart caused by salinity depresgrabs 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 mercenunder 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 rainmeasurement, i.e., anterior-postedor distance). fall in upstate Georgia. Becauseof adroughtin l98l,salinStation I was located in the Skidaway River approxiities were not depressed in winter/spring and a significant mately I mile south of the Skidaway Institute of Oceanset 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 drawan important source of food for many commercially valubridge 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 oplow water. Station 3 was located at the junction of Skidportunistic species such asM. lateralis.We describe here the away and Wilmington rivers, where the clams occurred in a productionof asinglecohortage-class of M. lateralisfollowsandy mud substrate in approximately 2 m of water at ing the 1981 set of thisbivalve after severalyears of recruitmean 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). Semidried to constant dry weight at 80oC for 48 h. diurnal tides average 2.4 m, with spring tides ranging apSecondary production was calculated using the instanproximately 3.4 m (Hubbard et al. 1979).Water temperataneous 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 where P = production in grams 'm-2, G = instantaneous 357 Manuscript received April 23, 1 9 84 ; accepted May 1 4,1 9 84 3s8 WALKER AND TENORE Figure l. The distribution and relatiye abundance of Mulinia loterolis in Wassaw Sound, Georgia. Letters below the density-symbols refer to substrate type: sh = shell, cs = coarse sand, s = sand, s/m = sandY mud, and m = mud. growth for the time interval, and B = mean standing crop between giventime intervals (B= [Bt + Bt+r ]/2). Instantaneous growth rate (G) is calculated as ln(W/Wo) where o and t represent the beginning and end of each time interval. Annual production is equal to the summation of the individual intervals' production estimates. Individual weights for the table were obtained by taking the mean of the clam lengths per month per station and applying that value to the shell-length to dry-weight regression equation. Growth was determined by plotting the mean weight of the clams against time. Mean weights were determined using monttrly mean shell lengths and converting to biomass.

Growth and Production of the Dwarf Surf Clam Mulinia lateralis (Say 1822) in a Georgia Estuary