Meiofauna and benthic microbial biomass in a semi-enclosed Mediterranean Marine system (Stagnone of 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 N­S transect characterized by different hydrodynamic regimes. Total sedimentary organic matter concentration ranged from 5.68± 1.11 to 156.28±12.63 mg g-1 , 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, 112± 29 ind.=10cm-2 and largely dominated by nematodes (on annual average from 40% to 91% of total meiofaunal density). Benthic microbial density ranged from 0.22±0.02 × 109 to 106.83± 16.77×109 g-1 sediment dry weight (DW). Microbial biomass ranged from 0.01± 0.003 to 7.04±0.14 mg Cg-1 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 μg g-1 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. [ABSTRACT FROM AUTHOR]