Plankton ecology and productivity, nutrient chemistry, and hydrography of Tasman Bay, New Zealand, 1982-1984

Abstract

The water column at a single near‐shore location in Tasman Bay was intensively sampled between April 1982 and March 1984 at 1–2 month intervals. Lowest salinities and highest dissolved nutrient concentrations occurred during the winter of both years. Nitrate‐N was the most commonly measurable inorganic nitrogen species. Inorganic N: P: Si ratios suggest that among the major nutrients nitrogen was in the greatest demand. The phytoplankton community structure and phenology was typical of a temperate neritic environment, though considerable year to year variations occurred in the specific composition and the magnitude of production. Periods of relative abundance of some potential nuisance species were documented. Small nannoplanktonic species (< 10 μm) were always an important and frequently a dominant component of the photosynthetic community. The winter/spring diatom bloom re‐occurred as the most productive event. In surface waters, phytoplankton biomass ranged from 19–208 mgC m‐3. In situ rates of photosynthesis ranged from 202–1981 mgC m‐2d‐1. The magnitude of phytoplankton blooms appeared to be related to preceeding high rainfall events. Unusually large floods during the winter of 1983 lead to a major peak in productivity by a mixed diatom/Mesodinium rubrum bloom. Annual net productivities of 121 gC m‐2y‐1 and 171 gC m‐2y‐1during 1982 and 1983 respectively, were estimated. © Crown 1986.