A preliminary study of the reproductive ecology of the seastars Asterias vulgaris and A. forbesi in New England

Individuals of the carnivorous forcipulate asteroids Asterias vulgaris and A. forbesi occur in low intertidal and subtidal regions in New England. They occupy both hard- and soft-bottom habitats, but greatest densities occur around high concentrations of their preferred prey, mussels. Mean wet weight varied both among sites [from about 1 to 90 g (A. vulgaris) and 1.4 to 32 g (A. forbesi)], and within sites (e.g., mean wet weight declined from 90 to 6 g in 12 months at one site).

Both seastars broadcasted eggs and sperm in late spring and summer at various sites between 1973 and 1975. In Massachusetts, A. vulgaris spawned in June and A. forbesi spawned in July or August, while in Maine, A. vulgaris spawned in July. In Maine, gonad and pyloric caecum cycles were inversely correlated in A. vulgaris, with peak gonad size occurring in June 1973. In contrast, in Massachusetts, organ cycles were uncorrelated in either species. At sites with dense mussel populations, individuals of both seastars developed larger gonads than at sites with sparse mussel populations. Reproduction (and growth) in these species is thus flexible, and depends on prey abundance. Dissection of ripe seastars over a range of sizes indicates that both species reach reproductive maturity at small size, between about 1 and 10 g. These results contrast to those obtained for the west coast seastar, Pisaster ochraceus, in which reproductive maturity is not attained until a size of 70–90 g wet weight, and in which organ cycles seem consistently inversely related. I postulate that these differences in size of sexual maturation are due to higher mortality of larvae in the plankton on the west than on the east coast of North America. I further suggest that high larval mortality requires growth to large size before maturation because lifetime production of gametes needed for replacement of a female is high, while lower larval mortality permits reproduction at small size because lifetime production of gametes for replacement of a female is lower.