LABILE ORGANIC-MATTER AND MICROBIAL BIOMASSES IN DEEP-SEA SEDIMENTS (EASTERN MEDITERRANEAN-SEA)

The distribution and the biochemical composition of organic matter were analysed in surface sediments (0-15 cm) of 22 continental and bathyal stations (110-2401 m; Ionian and Aegean Seas). Variations of labile organic matter (LOM), total organic matter (TOM), bacterial density and biomass were related to the benthic bacterial populations and to the environmental conditions. TOM was significantly correlated with water depth, but not with LOM, which was mostly composed of carbohydrates (89.6%) followed by proteins and lipids (5.4 and 5.0%). LOM ranged between 1.5 and 2.7 mg g-1 sediment dry weight, declining in concentration from the sediment surface to 15 cm depth. Bacterial counts ranged between 0.16 and 9.42 x 10(8) cells g-1 sediment dry weight. Bacterial density and biomasses in surface sediments (0-1 cm) were significantly correlated with carbohydrates and DNA concentrations. Although the overlying waters are oligotrophic and low concentrations of TOM are present, the relatively high percentage of LOM and bacterial density suggest that organic matter in deep-sea sediments of the Eastern Mediterranean Sea is not totally depleted of nutritional value.