Meiofauna and benthic microbial biomass in a semi-enclosed Mediterranean marine system (Stagnone di Marsala, Italy)

Microbial and meiofaunal dynamics and their relationships with the biochemical composition of the sedimentary organic matter were investigated in a semi-enclosed marine system (Marsala lagoon, Western Sicily, Mediterranean Sea). Sediment samples were collected on a monthly basis from March 1996 to February 1997 in four stations located along a N–S transect characterized by different hydrodynamic regimes. Total sedimentary organic matter concentration ranged from 5.681.11 to 156.2812.63 mg g1, while the biopolymeric fraction of organic carbon (BPC, measured as sum of the lipids, carbohydrates and proteins) accounted for only a small fraction (24%) of total organic matter. Total meiofaunal density was extremely low, accounting for, on annual average, 11229 ind.=10 cm2 and largely dominated by nematodes (on annual average from 40% to 91% of total meiofaunal density). Benthic microbial density ranged from 0.220.02109 to 106.8316.77109 g1 sediment dry weight (DW). Microbial biomass ranged from 0.010.003 to 7.040.14mg Cg1 sediment DW and accounted for a significant fraction of BPC at all stations (10%). Low chlorophyll-a concentration in the sediments of the Marsala lagoon (on annual average from 2 to 16 mgg1 sediment DW) suggests that organic detrital and heterotrophic bacteria largely dominate the sedimentary organic matter and do not promote the transfer of carbon towards the higher trophic state.