Benthic community structure characterization of the bed-sediment layer composition in the Musura Bay and Sakhalin area

Abstract

The aim of this study was to assess the existing benthic organisms of the Musura Bay and Sakhalin area, in order to evaluate the habitat status within these areas. Musura Bay and Sakhalin Area belong to the avandelta, part of the Danube Delta Biosphere Reserve (DDBR). The ecological evolution of the Musura Bay and Sakhalin Area was significantly distressed by the hydro morphological changes developed in the catchment and by the local environmental circumstances. The two investigated areas are exposed to both continental and marine impacts, been marked by rapid changes in local environmental conditions (i.e., salinity levels, water transparency, temperature, pH, dissolved oxygen concentration, wind speed etc.). At present, salinity has become an extensive threat to the structure and ecological functioning of coastal wetlands. For instance, salinity long-term monitoring showed a variation from 12 ‰ (in 1942) to 0.2 ‰ (at present) for Musura Bay, whereas for Sakhalin area the salinity is 6.9 ‰ (at present). In order to evaluate the interactions of benthic organisms and their natural environment, several analyses were performed (i.e., water quality status and the nature of the bed sediments). Results
revealed that the surface water quality is generally included in good-moderate category, even if some inadvertences were encountered as a result of local environmental conditions. Based on the obtained results, the nature of the bed sediments from Musura Bay and Sakhalin area, can be included in the terrigenous (siliciclastic) rich-sediment type with values higher than 50% of the total weight of dry residue. The faunistic research highlighted the presence of 17 taxa belonging to 11 major invertebrate taxonomic groups for the Musura Bay and the presence of 46 taxa belonging to 20 groups in the Sakhalin Area. The average general density of the benthic populations in the Musura Bay was 8 times smaller than in the Sakhalin Area. This study indicated that most of the identified species seem to be extremely tolerant to temperature and salinity variations.