POPULATION ECOLOGY AND SECONDARY PRODUCTION OF THE POLYCHAETE LOIMIA-MEDUSA (TEREBELLIDAE)

In soft-sediment marine and estuarine habitats, population dynamics of resident species are an important aspect of community structure and f unction, yet the population dynamics of many members of these communit ies remain poorly studied. The population dynamics and secondary produ ction of the infaunal terebellid polychaete Loimia medusa (Savigny) we re investigated in a shallow sand habitat of the York River, Chesapeak e Bay, Virginia, between June 1989 and December 1990. Monthly sampling throughout 1 yr revealed that individuals were present year-round wit h maximum densities of 60 ind m(-2) and a life span of 1 yr. Abundance s were highest from August through September when two cohorts recruite d to the population. Mean individual growth was highest in summer, and appeared to be a function of temperature rather than food limitation. Adults were reproductive from May through October and exhibited high fecundity; the number of oocytes segment-l ranged from 201 to 15840 am ong worms. Larvae initially appeared approximately 1 mo after gametes were first observed in adult L. medusa, and these larvae appeared to s pend less than 1 mo in the plankton. Abundances of larvae in the water column were significantly higher around new moon, suggesting lunar sp awning periodicity. New recruits attained sexual maturity within 2 mo of settlement. Secondary production was 3.3 g ash-free dry wt m(-2) yr (-1) and the P/B (production/ biomass) ratio was 3.0. Despite equilibr ium species characteristics such as large size, high fecundity, and pl anktonic larvae, L. medusa exhibits some characteristics typically asc ribed to opportunistic species, namely, the capacity for rapid growth and maturation, a short life span and a relatively high P/B ratio. Thi s mixture of life history characteristics emphasizes that there is no simple dichotomy between opportunistic and equilibrium species. We cau tion that the dominance of large infaunal polychaetes in soft-bottom e stuarine and marine environments may not be a useful indicator of undi sturbed habitats.