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

Abstract

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 5.68 ± 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./10 cm⁻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 C g⁻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.

Keywords:

• Sedimentary organic matter
• Benthic microbial community
• Meiofauna
• Mediterranean lagoon

Acknowledgements

This work was supported by a grant of the Ministero dell'Universita` e Ricerca Scientifica e Tecnologica and Ministero per le Politiche Agricole e Forestali, Italy.