Patterns and causes of temporal variability in the physiological condition of the phytoplankton community in Kaneohe Bay, Hawaii

Abstract

Primary production rates, the percentage of photosynthetically fixed carbon allocated to protein, production/biomass (P/B) ratios and water quality parameters were measured on a weekly basis over 1 year in Kaneohe Bay, Hawaii. The temporal sequence of virtually all parameters measured, with the exception of phosphate and ammonium concentrations, was significantly non-random ( P ≤ 0.05). Some of the parameters showed clear evidence of seasonality (e.g. nitrate and silicate concentrations, temperature, irradiance). However, the non-random nature of the temporal sequence in many parameters was typically due to 3- to 4-week periods during which the phytoplankton community composition and physiological state showed little variation. Both the percentage of fixed carbon allocated to protein and P/B ratios were negatively correlated with the phytoplanktoa size during all seasons, a result which suggests that the smaller cells were growing more rapidly than larger cells in both a relative and an absolute sense. Ammonium concentrations were consistently higher than nitrate concentrations, but of the nutrients measured only nitrate concentration was consistently correlated with per cent protein and P/B ratios. It is suggested the influx of nitrate to the system influences the supply of all forms of nitrogen via recycling within the food web, and the flux of nitrate is positively correlated with nitrate concentration.