We examined heterotrophic bacterial nutrient limitation at four sites in Florida Bay, U.S. in summer 1994 and winter 1995. Bacterial growth and biomass production in this system were most limited by inorganic phosphorus (P) in the eastern and southern regions of the bay. Nutrient additions stimulated 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 alkaline 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 levels were higher in the northwest and north-central regions and P-uptake into particles > 1 μm, primarily phytoplankton, was also higher in these regions. Consistent with these observations, others have observed that P is advected into the bay primarily in the northwestern region. Abundant seagrasses in Florida Bay may promote heterotrophic bacteria/production relative to 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, and light levels reaching the benthic plants are high.
Bibliographical noteFunding Information:
This research was supported by the National Oceanic and Atmospheric Administration’s Coastal Ocean Program. Logistical support was provided by personnel at the Keys Marine Laboratory, Florida. Site maps were generated from the Generic Mapping Tools web page: Weinelt, Martin <firstname.lastname@example.org>. ‘Online Map Creation.’ -Internet WWW Page, at URL: <http://www.aquarius.geomar.de/omc/>, (version current at: May 17, 1998). B. Biddanda provided comments on a previous version of this manuscript.