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In this paper, we describe the pelagic and benthic ecosystem of the Golden Horn  estuary opening into the Marmara Sea. To improve the water quality of the estuary, which had long been subject to severe anthropogenic pollution (industrial, chemical, shipping),  industrial facilities were moved from the estuary in the 1980s, followed by a rehabilitation plan in the 1990s. Our results, based on chemical parameters and phytoplankton showed some signs of improvement of water conditions in the upper layer. However, macrozoobenthic findings of this study did not reflect such a recovery in bottom life.An approach to the Ecological Quality Status (EQS) assessment was performed by applying the biotic indices BENTIX, AMBI, BOPA, BO2A. Our final assessment was based on 'expert-judgements' and revealed a very disturbed overall ecosystem with 'bad' EQS for the station at the head of the estuary,  'poor' in the rest of the estuary and 'moderate' EQS only in the middle station.

Soft-bottom material collected from the northern part of the Sea of Marmara (off Küçükçekmece) included a total of 67 species belonging to 24 polychaete families. Three species (Brania pusilla, Lysidice cf. margaritacea and Sabellaria spinulosa) are new records for the Sea of Marmara. Three alien species (Polydora cornuta, Prionospio pulchra and Pseudopolydora paucibranchiata) were found at the shallow-water stations. Different polychaete assemblages occurred in the area and the mud percentage of sediment and salinity were the main factors related to their distribution. A new Polydora species, which is mainly characterized in having brownish pigmentation solely on the antero-dorsal sides of the body, and falcate major spines with only a bulge (anterior ones) or with a bulge and a small tooth, is described.

This study was carried out to explore the effectiveness of different biotic indexes in the Marmara Sea. The assessment of ecological quality status (EQS) was performed by applying the biotic indexes BENTIX, AMBI, BOPA, BO2A and Shannon-Wiener diversity, in combination with the estimation of total organic carbon (TOC) content of sediments. BOPA and BO2A indexes tended to overestimate the EQS of the stations. BENTIX was the most efficient index as it demonstrated conceivable EQS results with respect to TOC load and successfuly determined "acceptable" or "not acceptable" status of the stations. TOC content of sediment, which significantly correlated with several benthic measures (S, N, AMBI, BENTIX), proved to be a valuable proxy measure in evaluating the likelihood of benthic impairment. When overall EQS of northern Marmara Sea was discussed, the region was designated as ecologically disturbed with only 25.7% of the stations in acceptable status.

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