Seasonal dynamics of prokaryotic abundance and activities in relation to environmental parameters in a transitional aquatic ecosystem (Cape Peloro, Italy)

This study examines the effects of temporal changes on microbial parameters in a brackish aquatic ecosystem. To this aim, the abundances of prokaryotes and vibrios together with the rates of enzymatic hydrolysis of proteins by leucine aminopeptidase (LAP), polysaccharides by ß-glucosidase (GLU) and organic phosphates by alkaline phosphatase (AP), heterotrophic prokaryotic production (HPP), respiration (R), were seasonally investigated, during a two years period in the coastal area of Cape Peloro (Messina, Italy), constituted by two brackish lakes (Faro and Ganzirri). In addition, physical and chemical parameters (temperature, salinity, nutrients) and particulate organic carbon and nitrogen (POC, PN) were measured. The influence of multiple factors on prokaryotic abundances and activities was analysed. The results showed that Cape Peloro area is characterised by high seasonal variability of the microbial parameters that is higher than the spatial one. Combined changes in particulate matter and Temperature (T), could explain the variability in vibrios abundance, GLU and R activities in both lakes, indicating a direct stimulation of the warm season on the heterotrophic prokaryotic metabolism. Positive correlations between T (from 13.3 to 29.6°C) and HPP, LAP, AP, POC, PN are also observed in Ganzirri Lake. Moreover the trophic status index and most of the microbial parameters show significant seasonal differences. This study demonstrates that vibrios abundance and microbial activities are responsive to the spatial and seasonal changes of examined area. The combined effect of temperature and trophic conditions on the microbial parameters lead us to suggest their use as potential indicators of the prokaryotic response to climate changes in temperate brackish areas.