Nutrient limitation of heterotrophic bacteria in Florida Bay

We examined heterotrophic bacterial nutrient limitation at four sites in Fl orida Bay, U.S. in summer 1994 and winter 1995. Bacterial growth and biomas s production in this system were most limited by inorganic phosphorus (P) i n the eastern and southern regions of the bay. Nutrient additions stimulate d productivity and biomass accumulation mostly in summer. The magnitude of growth responses (thymidine incorporation) to nutrient additions was nearly an order of magnitude less in winter than summer. Biomass-normalized alkal ine phosphatase activity in the northeast and south-central region was 5-20 times greater than in the northwest and north-central regions, suggesting that P is most limiting to planktonic growth in those areas. Chlorophyll le vels were higher in the northwest and north-central regions and P-uptake in to particles > 1 mum, primarily phytoplankton, was also higher in these reg ions. Consistent with these observations, others have observed that P is ad vected into the bay primarily in the northwestern region. Abundant seagrass es in Florida Bay may promote heterotrophic bacterial production relative t o phytoplankton production by releasing dissolved organic carbon that makes bacteria more competitive for limiting quantities of inorganic phosphate, especially in the eastern bay where turbidity is low, P is most limiting, a nd light levels reaching the benthic plants are high.