The effects of sewage discharges on shallow hard substrate macrozoobenthic communities in the Bosphorus

Abstract

In order to determine the pollution effects of sewage discharges on the benthic communities, shallow water hard bottom macrozoobenthic communities were examined along the coasts of the Bosphorus Strait. Samples were collected at 15 stations and environmental parameters measured at 3-month intervals from May 2004 to February 2005. While 9 stations were selected as discharge stations, 6 stations were selected as control stations. A total of 180 samples were collected in May, August and November 2004 and February 2005. Samples were collected from the upper infralittoral zone at dept range 0.5-1m. The analysis of 180 quadrate samples yielded a total of 167537 individuals belonging to 85 taxa. These are distributed qualitatively among the taxonomic groups as follows: Crustacea 50.59% (43 taxa); Polychaeta 21.18% (18 taxa); Mollusca 14.12% (12 taxa); Nemertea 3.53% (3 taxa); Turbellaria 3.53% (3 taxa) and other groups Cnidaria (2 taxa), Oligochaeta (2 taxa), Pycnogonida (1 taxa) and Echinodermata (1 taxa). Individuals, on the other hand, these are distributed among the taxonomic groups quantitatively as follows: Crustacea 43.99% (73919 ind.); Mollusca 37.25% (62258 ind.); Polychaeta 11.06% (18490 ind.); Oligochaeta 5.79% (9681 ind.) and other groups Turbellaria (1899 ind.), Nemertea (799 ind.), Cnidaria (385 ind.), Pycnogonida (121 ind.) and Echinodermata (5 ind.). With regard to qualitative and quantitative dominance, Crustacea was the most important taxonomic group in the area investigated. Various univariate, graphical/distributional, multivariate statistical methods and BENTIX index were employed to analyze the data collected from the study area. Analysis of the data revealed clear differences between the sampling sites subjected to sewage discharge and the others. The results suggested that the benthic ecosystem was more or less disturbed in stations subjected to sewage. The typical characteristics of the benthic communities exposed to pollutants such as the prevalence and high dominance of the opportunistic species, low number of species, low diversity and multi-metric benthic index scores and low total faunal abundance were encountered in most of these stations. On the contrary, it could be said that benthic communities was appeared to be healthier in stations non exposed to sewage, characterized by the high number of species, high total faunal abundance, high diversity and multi-metric benthic index scores. It can be construed that the effects of pollution on these communities was quite low. There is now almost adequate information about the effects of sewage discharges on shallow water hard substratum macrozoobenthic communities, although open questions. The present work has also provided a base for further biomonitoring studies.