No abstract

In order to estimate the qualitative variation of sedimented mussel deposits, biochemical and microbial measurements were undertaken after a sediment enrichment with fresh faeces and pseudo-faeces collected in a mussel farming area (Carteau, Gulf of Fos).During two months, cores sampled were investigated at three stations: a first station enriched with mussel deposits, a second considered as a reference station without mussel deposits and occasionally a third corresponding to a continuously enriched sediment under a rope culture.Carbohydrate, organic carbon and nitrogen contents in the sediments gave evidence of a short term variation after sedimentation.Bacterial production increased rapidly at the enriched station and returned to its initial level 8 days later. At this station, exoglucosidasic activity of bacteria, low at the beginning, presented a maximum two weeks after enrichment whereas exoproteolytic activity, which was high in the biodeposits, decreased in the course of the first week. These exoenzymatic activities were significantly higher at the enriched station than at the reference stations. Carbohydrate measurements were in agreement with these results.Degradation rate of biodeposits is discussed on the basis of exoenzymatic activity, organic carbon, nitrogen and free amino acid content at the three stations.

The composition of the surface microlayer was compared at two sites, having different degrees of water pollution, near the northern Mediterranean coast. Harvey (rotating drum device) and Garrett (screen) samplers were used and their effectiveness compared; the enrichment factor shown was greater with the former. Eutrophication due to river runoff and hydrocarbon pollution from refinery effluents may contribute to an increase in the enrichment factor. Differences in chlorophyll, ATP, and pheophytin content between the two sampling methods suggest stratification of the living and inert planktonic material.