Growth of the bivalve Nucula annulata in nutrient-enriched environments

Abstract

Examined Nucula annulata from unstressed and nutrient-enriched environments in Narragansett Bay, Rhode Island. Clams from unenriched environments grew between 0.55 and 0.9 mm yr-1. Significant growth was limited to temperatures between 10-20°C, in late spring and early fall. Populations in unstressed environments were dominated by high abundances of small clams (<1mm in length). Populations from nutrient-enriched environments consisted of fewer, larger clams. Larger individuals are apparently simply older clams rarely found in unenriched environments. δ18O temperature values from shell growth bands indicated a shift in the season of maximum growth from spring to summer for clams in eutrophic environments. Peak spawning activity of N. annulata usually coincides with the summer maxima in temperature (22°C) The low numbers of juveniles found in enriched environments coupled with warmer shell growth temperatures imply a decline in successsful reproduction and/or recruitment in eutrophic areas. Deteriorating environmental conditions associated with nutrient enrichment (low water column oxygen levels) may also enhance the survivorship of older, larger N. annulata possibly through a reduction in predation pressure. -from Author