Alkaline phosphatase activity of seagrass and water column fractions in Florida Bay

Few phosphorus (P) depleted coastal marine ecosystems have been examined for their capacity to hydrolyze phosphomonoesters (PMEs). The purpose of this study, was to examine seasonal APA partitioning between water column fractions (phytoplankton, bacteria and freely dissolved) and benthic autotrophs in Florida Bay, a P limited shallow estuary using low fluorescent substrate (MUF-P) concentrations (≤2.0 muM). APA was higher at the western and northcentral (751 and 695 nmol L-1 h-1) sites and driven by cyanobacterial blooms, compared to the P limited northeastern (359 nmol L-1 h-1) site. The free dissolved fraction (<0.2 mum) accounted for the most APA (∼50%), followed by the phytoplankton (>1 mum; 30%) and bacteria fraction (<0.2->1.2 mum; 8%). Thalassia testudinum leaves with their associated epiphytes contributed modestly to water column APA (14 and 20%), and only during non-bloom conditions. Rapid hydrolysis of PMEs (undetected in most samplings) in Florida Bay is probably driven by high concentration of organic substrates for microbial and cyanobacterial activity which results from the close association of the shallow water column with the underlying seagrass community and adjacent Everglades wetlands.