MEPS 165:45-57 (1998)  -  doi:10.3354/meps165045

Microbial plankton response to resource limitation: insights from the community structure and seston stoichiometry in Florida Bay, USA

Peter J. Lavrentyev1,*,**, Harvey A. Bootsma1,***, Thomas H. Johengen1, Joann F. Cavaletto2, Wayne S. Gardner2,**

1University of Michigan, Cooperative Institute for Limnology and Ecosystem Research, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109, USA 2National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, 2205 Commonwealth Boulevard, Ann Arbor, Michigan 48105, USA
Present addresses:
**University of Texas at Austin, Marine Science Institute, 750 Channelview Drive, Port Aransas, Texas 78373, USA
***SADC / GEF Lake Malawi / Nyasa Biodiversity Conservation Project, PO Box 311, Salima, Malawi

Concentrations of dissolved and particulate nutrients, chlorophyll, and microorganisms (0.01 to 200 µm) were simultaneously measured during a 1 d survey of 12 stations in Florida Bay, USA, to characterize the microbial plankton community with respect to resource limitation. Three distinct types of trophic conditions, reflected in seston elemental stoichiometry and community structure, were identified within the bay. The first type, characteristic of the isolated eastern region, had low nutrient concentrations, imbalanced stoichiometry, and small microbial biomass with a large proportion of bacteria. The microbial community in this region was characterized by weak relationships between microzooplankton and phytoplankton and the predominance of mixotrophic taxa and the autotrophic ciliate Mesodinium rubrum. The second type, found in the north-central region influenced by Taylor Slough inflow, had elevated nutrient concentrations, elemental stoichiometry skewed toward N, and high turbidity. Under these conditions, the picocyanobacterium Synechococcus formed a dense bloom and coincided with an abundant, multi-step microbial food web. Finally, at the boundary with the Gulf of Mexico, low concentrations of nutrients were balanced at approximately the Redfield ratio and supported nanophytoplankton that were tightly correlated with microzooplankton. These data are consistent with the notion of P limitation in Florida Bay but also demonstrate that Si, light, and N may be co-limiting to phytoplankton in the eastern, north-central, and western boundary regions, respectively. Our findings suggest that multiple resource gradients, in conjunction with microbial food web processes, are important factors determining the plankton community structure in Florida Bay and should be considered in studies on ecological disturbances.

Subtropical lagoon · Nutrient limitation · Seston stoichiometry · Phytoplankton · Microbial food web

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