ABSTRACT
New York Harbor receives continuous inorganic nutrient inputs from waste discharge and urban runoff at levels saturating to phytoplankton growth. The annual cycle of diatom (Skeletonema costatum) dominance in late winter-early spring, followed by succession to green algal nanoplankton (Nanochloris atomus) in late spring through fall was considered in the context of a light limitation hypothesis. The diatom peak is explained by this hypothesis, but late spring succession to nanoplankton seems anomalous in terms of existing models of phytoplankton composition in estuaries. Under optimal light and temperature, cultured S. costatum grew poorly (<1 doubling/d) in New York Harbor water collected during the succession period; N, P, and Si were well above limiting levels. However, Si, trace element, or vitamin enrichment restored growth (1-2 doublings/d) during portions of this period. Autoclaving the water also resulted in growth restoration. Apparently dissolved substance (e.g. toxins, chelators) interfere with diatom growth, possibly resulting in succession to green algal nanoplankton. This possibility supports existing models of the effects of perturbation on phytoplankton composition and is reflected by a model of light limited phytoplankton production. Implications of the data to current water quality management schemes are considered.
