SPAWNING CYCLE, FECUNDITY, AND RECRUITMENT IN 



A POPULATION OF SOFT-SHELL CLAM, MYA ARENARIA, 



FROM CAPE ANN, MASSACHUSETTS 



Diane J. Brousseau* 



ABSTRACT 



A population ofMya arenaria in the Annisquam River system, Gloucester, Mass. , was studied for 3 yr to 

 determine spawning frequency, fecundity, and recruitment rates under natural conditions. This 

 population was observed to spawn twice each year, in March-April and June-July. Temperature 

 appeared to be a more critical factor in the timing of gonad maturation than in triggering the release of 

 gametes. Female body sizes and oocyte production were positively correlated (1973, r = 0.95; 1974, 

 r = 0.90). Regression lines were compared by analysis of covariance. Slopes of the lines did not differ 

 significantly between years or between spawning cycles within years (P 3^0.05). Elevations of the lines 

 differed significantly from one another (P«0.05) indicating annual and seasonal variability in fecun- 

 dity. Sex ratios of Af. arenaria 25-95 mm shell length did not differ significantly from 1:1 over the 3-yr 

 study period. In smaller individuals, male and female gonads were indistinguishable. No evidence of 

 hermaphroditism or protandry was observed. Recruitment rates of juveniles fluctuated widely between 

 spawning cycles as well as between years. 



Although the literature contains widely scattered 

 references to the reproductive cycle of Mya 

 arenaria in New England, there is no combined 

 account of egg production ( = fecundity), spawn- 

 ing, and recruitment of this species under natural 

 conditions. Inferences about the time and fre- 

 quency of spawning by M. arenartia have been 

 made from observations on larvae in the plankton 

 (Stevenson 1907; Stafford 1912; Sullivan 1948; 

 Landers 1954; Pfitzenmeyer 1962); from first ap- 

 pearances of newly settled juveniles (Belding 

 1930; Warwick and Price 1975); and from the 

 presence of ripe gametes in the gonads (Battle 

 1932; Coe and Turner 1938; Shaw 1962; Stickney 

 1963; Ropes and Stickney 1965; Munch-Peterson 

 1973; Porter 1974). Observations on larvae and 

 recently metamorphosed clams, however, are use- 

 ful only as indirect measures of the frequency and 

 duration of spawning, since larval abundance and 

 juvenile recruitment are controlled by factors 

 other than spawning alone. Conversely, evidence 

 concerning gonad maturation and gamete release 

 obtained by means of histological methods defines 

 the spawning period without contributing to 

 knowledge about recruitment. 



'Department of Biology, Fairfield University, Fairfield, CT 

 06430. 



Manuscript accepted July 1977. 



FISHERY BULLETIN: VOL. 76, NO. 1, 1978. 



Most shallow-water marine animals reproduce 

 in a cyclic manner, the time of spawTiing ulti- 

 mately depending on environmental factors (Or- 

 ton 1920; Giese 1959; Kinne 1963). As with most 

 other commonly studied bivalves, the timing of 

 spawning by M. arenaria has been linked to water 

 temperatures (Nelson 1928; Belding 1930; Battle 

 1932). Nevertheless, it remains unclear whether 

 gametogenesis, spawning, or both occur at a 

 specific temperature or in a specific temperature 

 range in M. arenaria. 



Reliable information on fecundity of M. 

 arenaria is also unavailable. Laboratory methods 

 for stripping eggs or inducing spawning in oysters 

 and hard-shell clams (Brooks 1880; Churchill 

 1920; Galtsoff 1930; Belding 1930; Davis and 

 Chanley 1956; Loosanoff and Davis 1963) are gen- 

 erally unsuccessful with M. arenaria. Conse- 

 quently, the only information on egg production 

 by M. arenaria is an unsupported statement by 

 Belding (1930) that a 2.5-in clam (63 mm) pro- 

 duces about 3 million eggs per breeding season. 



In an effort to clarify the breeding habits of M. 

 arenaria, this study was designed to determine 1) 

 the reproductive cycle in a natural population, 2) 

 the temperature at which gametogenesis and 

 spawning begin in this locale, and 3) the total 

 numbers of eggs produced by individuals of differ- 

 ent sizes. 



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