AUTECOLOGICAL STUDIES ON THE MARINE DIATOM RHIZOSOLENIA FRAGILISSIMA BERGON. II. ENRICHMENT AND DARK VIABILITY EXPERIMENTS1

Abstract

SUMMARYNutrient enrichment experiments were conducted with a Narragansett Bay clone of Rhizosolenia fragilissima to examine the potential influence of nutrients in regulating its seasonal cycle in this embayment, and their contribution to its coastal tendencies. Growth rates were measured at 18 C and 1000 ft‐c continuous illumination in surface waters enriched in 15 different ways. Narragansett Bay was sampled in March, May, September, and December. Six stations on a transect from this Bay to the Sargasso Sea were sampled during late summer.The data and our previous autecological observations are consistent with the idea that the annual cycle of this species in Narragansett Bay is associated with temperature, chemical “water quality,” and unknown factors. Its absence during late fall and winter may reflect low temperatures and a trace metal (Co, Mo) inadequacy. In early spring, low temperature appears to be the limiting factor, whereas in late spring and early summer trace metals again appear to prevent active growth. A late summer‐early autumn bloom occurs periodically during optimal temperature conditions; this can terminate independently of grazing pressure, and in spite of seemingly adequate light‐temperature‐salinity and phosphate conditions.