Microbial metabolism and turnover of organic matter in the euphotic layer of Sicilian Channel

With the aim of providing an ecosystem approach to fisheries management, the monitoring of biological and environmental information was carried out during two oceanographic cruises (BANSIC 2012-13) performed in the Sicilian Channel in different seasonal conditions. The Sicilian Channel is a spawning area for the Engraulis encrasicolus (Linnaeus, 1758), a small pelagic species of commercial interest. The prokaryotic abundance and biomass as well as their hydrolysis rates on organic matter were investigated at selected stations in the euphotic layer. The particulate organic carbon (POC) was generally low (68-70 µgL-1 in summer), as well as those of particulate nitrogen (PN), reflecting a pattern typical of oligotrophic areas. The prokaryotic abundance ranged between 1.0 and 1.9 x106 cell ml-1 in summer and 2.5 - 8.1 x 105 cell ml-1 in winter. The prokaryotic biomass varied from 24.9 to 113.0 µgCL-1 in summer and 0.038-0.71 µgCL-1 in winter. Total leucine aminopeptidase showed the highest rates, followed by alkaline phosphatase and beta-glucosidase in summer. During winter 2013 the alkaline phosphatase prevailed on aminopeptidase, potentially releasing 346-739 ngPL-1 for new production. The potential release of carbon ranged between 230 and 407 ngCL-1 in summer, while in winter it was 88 -158 ngCL-1. The contribution of dissolved enzymatic activities varied between the two years, accounting for 21-42% of released total carbon. The rates of total hydrolysis were comparable to previous data obtained from other oligotrophic Ionian and Mediterranean areas, while this study was the first report about the dissolved enzymatic fraction in the Strait of Sicily.