Fewer Species but More Existing Individuals: Testing the Hypothesis ‘Pessimum Conditions Rule’ Based on Long-Term Data of Species Composition of Benthic Fauna and Environmental Variables in the Sea of Marmara, Turkey

Abstract

The aim of this study is to try to prove the hypothesis that “When species diversity reduced, the survived unit members in the environment would be increased”, which named by us as “Pessimum conditions rule” in the scale of the Sea of Marmara. To prove the hypothesis “Pessimum conditions rule”, data from 604 observations both of benthic and oceanographically stations gathered in a 7-year period (2006-2012) were analyzed and compared, and the results used to show the relationship between classic biotic descriptors (e.g. number of species, number of individuals, richness index, dominance index, Shannon/Menhinick diversities) and environmental variables (e.g. Dissolved Oxygen, temperature, Salinity, pH) and depth. Multiple analysis of covariance and multiple linear regressions were used for the statistical analysis of the data. Correlations between benthic community indices and water quality variables showed that generally might affect community diversity. Besides this, it is clear that variation within benthic habitats in the Sea of Marmara cannot be explained by a single factor, such as uncontrolled overfishing and the revolving changes in the adjacent connected seas or driven by biotic interactions rather than by the water quality. According to the sample composition of benthic catches and related frequency values, a relative increase in the number of individuals was observed. This is also apparent by the correlation between basic pollution parameters and the community index values regarding long-term data of the present work. The measured values of the constant environment, created due to the unique structure of the Mediterranean originated lower layer of the Sea of Marmara, and correlated biotic parameters were showing a coherent dispersion in the completely sampling period. However, contrary to this, the values of the number of species were exactly the opposite. In the present study, pessimum conditions rule has been especially distinctive in the Sea of Marmara regarding the long-term data of the benthic catches. Also, this work report on species composition of the benthic catches in the Sea of Marmara for an assessment of the status of these communities and relation these communities with pollution phenomenon.