Growth and reproduction of the bay scallop, Argopecten irradians (Lamarck) at its southern distributional limit

Growth and reproduction in a Florida population of bay scallop, Argopecten irradians (Lamarck), existing at the southern limit of its distribution, was monitored over a 3-yr period. Somatic growth accompanied increasing water temperature between May and August, when maximum mantle, digestive gland, and adductor muscle weights and indexes were observed. From July through September, reproductive development was correlated with a decline in adductor muscle weight and index. Maximum gonad weight, gonad index, and oocyte diameter were found in late September and early October. Spawning commenced at this time in conjunction with decreasing water temperature.In comparison to more northern populations, the reproductive cycle of the Florida bay scallop occurs later in the year and is characterized by a higher gametogenic initiation temperature, a decreased maximum gonad index and decreased oocyte diameter, and a shift in reproductive energy resources from digestive gland (available food) to adductor muscle (pre-stored reserves). Increased metabolic rate associated with higher temperature and coupled with decreased food supply results in the Florida bay scallop having less energy available for reproduction, ultimately limiting its southern distribution.