Salinity and pH play a fundamental role in structuring spatial patterns of physical properties, biota, and biogeochemical processes in the estuarine ecosystem. In this study, the influence of salinity-pH gradient and carbonate system on polychaete diversity in Ennore, Uppanar, Vellar, and Kaduvaiyar estuaries was investigated. Water and sediment samples were collected from September 2017 to August 2018. Univariate and multivariate statistical analyses were employed to define ecological status. Temperature, salinity, pH, and partial pressure of carbon-di-oxide varied between 21 and 30°C; 29 and 39 ppt; 7.4 and 8.3; and 89.216 and 1702.558 µatm, respectively. PCA and CCA results revealed that DO, chlorophyll, carbonate species, and sediment TOC have a higher influence on polychaete community structure. Forty-two species such as Ancistrosyllis parva, Cossura coasta, Eunice pennata, Euclymene annandalei, Lumbrineris albidentata, Capitella capitata, Prionospio cirrifera, P. pinnata, P. cirrobranchiata, and Notomastus sp. were found dominantly in all estuaries. Shannon index values ranged between 1.619 (UE-1) and 3.376 (VE-2). Based on these findings, high levels of carbonate species and low pH have a greater impact on polychaete diversity and richness values. The results of the AMBI Index revealed that stations UE-1, UE-2, UE-3 in Uppanar, EC-1, EC-2 in Ennore indicate “moderately disturbed”, while other stations are under the “slightly disturbed” category. This trend was quite evident in M-AMBI as well.
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Polychaetes of the northwestern Black Sea (NWBS) were sampled in January 2005 at 4 sites comprising 32 stations. The 4 sites have different anthropogenic loads, different depths (<10 m, 11-20 m, 21-30 m, >30 m) and different substrates (shelly, silty). The species composition of polychaetes in Black Sea meiobenthic communities has not previously been studied. Twenty polychaete species belonging to 11 families, the Phyllodocidae, Nephtyidae, Polynoidae, Sigalionidae, Nereidae, Syllidae, Hesionidae, Protodrilidae, Spionidae, Capitellidae and Ampharetidae, were recorded. The polychaete density varied with depth and type of substrate from 500 ind. m-2 to 66,000 ind. m-2.