Short-term temporal and spatial dynamics of bacterioplankton near Barbados in the Caribbean Sea

Abstract

To investigate temporal (ca 1 mo) and spatial dynamics of bacterioplankton in the Caribbean Sea, time-series measurements of chlorophyll a concentration, bacterial abundance, and thymidine incorporation rate were performed at 6 stations near Barbados. In addition, a series of incubation experiments was carried out with seawater samples collected from various depths and stations to determine bacterial growth rates and removal rates by bacterivory. Vertically integrated phytoplankton and bacterioplankton biomasses averaged 1290 and 1200 mg C m-2, respectively, and heterotrophic bacterial production was 106 mg C m-2, with in situ bacterial growth of 0.1 d-1. Approximately halfway through the sampling period, surface salinity dropped by as much as 4 following the arrival of water from the Amazon River. No subsequent change, however, was noted in chlorophyll a concentration, bacterial abundance, or bacterial production. Averaged bacterial growth and bacterivory determined from bottle incubation experiments were 0.6 and 0.5 d-1, respectively, suggesting that predation was a major sink of daily bacterial biomass production. Both regression analysis of bacterial biomass and production and measurements of growth and bacterivory from incubation experiments suggest that top-down processes control bacterioplankton dynamics to a greater degree than bottom-up processes.