Intraspecific variation in reproductive and somatic growth cycles of bay scallops Argopecten irradians

Abstract

of intraspecific variabhty in fecundity, and reproductive and somatic (adductor muscle) growth cycles is exammed among 4 adjacent, New York populations of bay scallops Argopecten irradians Lamarck. Wd-latitude populations are compared to previously studied populations at the northern and southern extremes of the species' geographical distribution along the east coast of the USA. Major spawning occurred in early June, followed by secondary spawning in July and early August. Spawnlng intensity (percent of gonad evacuation during first spawning) ranged from 62 % at the shallower site (1 m) to 22 % at the deepest site (3.5 m). This difference is temperature related. Mean fecundity (annual egg production) - not previously reported for this species - was determined from weight loss on spawning. It ranged from 12.6 to 18.6 X 106 per 1st year scallop. Lndividuals that survived to a 2nd spawning averaged signif~cantlylo wer gonad output than expected from the hnear regression of log gonad weight on log shell height in younger scallops. Greatest differences In mean shell height, adductor muscle weight In the fall, and fecundity were observed between 2 adjacent sites only 1.5 km apart. Results of this study suggest that scallops are food limited within shallow, enclosed bays, where circulation is more restricted. Size-specific fecunhty of midlatitude New York bay scallops is 7 times greater than that of Florida scallops, at the southern limit of their distribution. The ratio of reproductwe output to somatic hssue weight of A. i. irradians is also 2 to 8 times greater than the maximum ratio attained by iteroparous, longer-lived pectinids. A persistent picoplanktonic bloom in summer 1985 caused starvation and 76 % reduction in muscle weight of adults relative to 1984. Following waning of the bloom, survivors displayed remarkable reshence, reflected in a 3-fold increase in mean muscle weight during September.