Enzymatic activity on sandy beaches of the Ligurian Sea (NW Mediterranean)

Enzymatic activity was measured on two beaches of the Ligurian Sea (NW Mediterranean) during late spring and summer 2003. The detected activities (leucine aminopeptidase, beta-glucosidase, alpha-glucosidase, and beta-N-acetylglucosaminidase) were related to the available organic substrates (proteins and carbohydrates) and to the bacterial community (expressed in terms of abundance, biomass, and frequency of cell division). The very low chlorophyll a concentrations (never higher than 40 ng g(-1)) suggested that heterotrophic microorganisms play a major role in the beach ecosystem. Enzymatic activities devoted to organic matter degradation were lower in the emerged part of the beaches and higher in the sites covered, permanently or temporarily, by seawater, suggesting that sea action enlivens the degradation processes. Leucine aminopeptidase ranged from 0.26 to 13.02 nmol g(-1)h(-1), and beta-glucosidase (the most expressed glycolytic enzyme) from 0.03 to 4.51 nmol g(-1)h(-1). Strong changes in the proteolytic/glycolytic activity ratio were observed, with a sudden rise in glycolysis during summer, leading to ratio values from about 30 down to 1. Thus, beaches were identified as preferential degradation sites, where very refractory compounds such as cellulose may also be efficiently processed.