Dynamics of extracellular enzymatic activities in a shallow Mediterranean ecosystem (Tindari ponds, Sicily)

Three microbial extracellular enzymes, leucine aminopeptidase (LAP), β-glucosidase (β-glu) and alkaline phosphatase (AP), were studied in six small Mediterranean littoral ponds, to evaluate the diversity of microbial activities relative to prevailing environmental conditions. The marked diversification of the trophic states, ranging from oligotrophy to eutrophy, in the ponds was reflected in a range of enzyme patterns at different spatial and temporal scales. There were higher levels and greater variability of microbial activity in the oldest and most 'confined' ponds (ranges: 0.55-4360.00 nM h -1 , 0.15-76.44 nM h -1 , 1.29-1600.00 nM h -1 for LAP, β-glu and AP respectively) compared with the youngest and most seaward ponds (ranges: 22.64-612.0 nM h -1 , 0.06-48.89 nM h -1 , 0.32-744.0 nM h -1 for LAP, β-glu and AP respectively). The close relationship of the degradative potential with chlorophyll-a and particulate organic carbon could be a consequence of the stimulating effect of phytoplankton-released polymeric compounds (organic matter) and/or a response of the microbial community to warm temperatures, which were recorded from July to September. Within an area less than 1 km 2 , different aquatic ecosystems coexist and maintain their distinctive properties in terms of microbial biogeochemical processes.