MOLLUSCAN ECOLOGICAL TRENDS ACROSS A HUMAN-IMPACT ORGANIC LOAD GRADIENT ALONG THE SOUTHEASTERN MEDITERRANEAN SHORE

Man-induced changes in the Israeli Mediterranean shore had a strong ecological imprint on the biota. This is especially true for the area of Palmahim, in the vicinity of the treated sewage sludge outlet. Macrobenthic invertebrates such as shelled mollusks are known to be sensitive indicators of seafloor oxygen levels, water energy and sediment mass properties. Investigating the death assemblage record of these organisms should capture the composition and community structure of the living community better than a short-term or single biological census due to the summing of seasonal and annual variations, and thus provide a more complete environmental picture.

A sub-sampling of box core sediment samples from an along-shore transect that crosses the treated sewage sludge area but also includes areas farther away from (station AS1) and peripheral (station PL29) to the main impact area were examined. Molluscan death assemblages from summer (07.03) and winter (01.04) from three stations were analyzed and species richness, evenness, relative and total abundance were calculated. Macrofaunal results from the area of the sewage outlet (station PL3-07.03) show that species richness and number of specimens per gram sediment are considerably lower than those from the peripheral stations PL29 and AS1. Unexpectedly, there is a considerable difference in species richness and total abundance per gram sediment between summer and winter in death assemblages from the treated sewage outlet station (PL3), similar to that seen in the live benthic foraminifera data. This may point to extremely high sedimentation rates for this station on the one hand and extremely strong impact of the sewage on the fauna on the other hand.