Horizontal and Seasonal Distribution of Zooplankton Biomass and Fluorescence from Mocness Plankton Tows in the Florida Straits and the Dry Tortugas

摘要

Nine biological-oceanographic SEFCAR (South East Florida and Caribbean Recruitment) cruises were conducted over a 2-year period, spring 1989 to spring 1991, along the continental shelf off southeast Florida between the Dry Tortugas and the Upper Florida Keys. A total of 1,140 discrete stratified zooplankton samples including zooplankton biomass (ml) and fluorescence (voltages) data were collected with MOCNESS nets at 253 stations. Horizontal distributions of zooplankton biomass and fluorescence were highly variable spatially and an offshore-offshore pattern was not clearly distinguished. Zooplankton biomass by station varied from 0.05 to 1.5 ml m(-3) with mean and standard deviation of 0.57 + or = 0.2 ml m(-3), and fluorescence varied from 0.35 to 11.5 vol m(-3) (2.71 + or = 1.9 volt m(-3)). Mean fluorescence calculated by cruise did not show a seasonal pattern or any effect with abiotic factors, except for the time of the day in which samples were collected. The lack of calibration of fluorescence to chlorophyll was a critical factor precluding the use of these fluorescence data as indicators of primary production. In contrast, a seasonal pattern was observed on the zooplankton biomass over the two-year period, decreasing from spring to summer and increasing from summer to fall. Zooplankton biomass during the winter cruises was highly variable, perhaps due to the different oceanographic conditions and transects between cruises. Mean zooplankton biomass was also useful as an indicator of oceanographic conditions.