PLANKTON STUDIES IN BUZZARDS BAY, MASSACHUSETTS, USA .1. HYDROGRAPHY AND BACTERIOPLANKTON, 1987 TO 1990

The hydrography, water chemistry and plankton communities of Buzzards Bay, Massachusetts, USA, a temperate estuary (41-degrees-N), were studied over 45 cruises (10 October 1987 to 11 September 1990). Surface temperature varied from -2.0 to 27.26-degrees-C (n = 360), but because of shallow depth (mean = 10 m), strong wind and tidal mixing, the water column was isothermal most of the year. The only thermal structure was found during the summer, when it was minimal and appeared to be a diel phenomenon, partly related to solar heating. Secchi disk readings ranged from 0.75 to 9.0 m (n = 352). Due to shallow depth most of the water column was in the euphotic zone (> 1 % of surface illumination) for most of the year. Exceptions were bay-wide levels of only 60 to 80 % of the water column being euphotic during each of 3 winters, as well as at the sewage outfall of the City of New Bedford throughout 3 years where regardless of season only 40 to 80% of the water column was euphotic due to light attenuation by fine particles of sewage sludge. Surface bacterioplankton abundance ranged from 0.30 to 10.92 x 10(6) cells ml-1 (n = 352), and fluctuations generally tracked those of temperature. The overwhelmingly dominant aspect of the water-column ecology of Buzzards Bay is high variability due to severe seasonality of physical parameters, particularly temperature.