Deep-sea soft bottom infaunal communities of the Levantine Basin (SE Mediterranean) and their shaping factors

The present study sought to quantify the infauna and environmental characteristics of the deep SE Levantine Basin, Mediterranean Sea (33.4–31.7 N, 31.3–34.9E; 100–1900 m water depth). Box corer samples were collected at 50 sites in June–July 2013. The infauna (>250 μm) were enumerated and identified to the lowest possible taxonomic level (~37 % to the species level). Three faunal assemblages were identified, inhabiting three biotopes, the shelf margin (SM), the continental slope (CS) and the bathyal plain (BP). The within-biotope heterogeneity was evaluated by the average Chao-Sørensen similarity index and the beta diversity (exp(gamma diversity)—exp(alpha diversity)), revealing values of 0.64–0.7 and 1.73–2.77, respectively, upon applying the pooled bathyal plain samples. The corresponding non-pooled samples revealed higher heterogeneity, with values of 0.26 and 6.27, respectively, likely due to insufficient sampling. The infaunal density in the various biotopes (geometric mean 59–2220 ind m^{− 2}) exhibited a logarithmic decline with water depth. The estimated number of taxa per biotope was calculated by rarefaction analysis in relation to the sampled area and the number of sampled individuals, resulting in 203 (sampled area)−206 (number of individuals) (SM), 170–163 (CS) and 144–130 (BP) taxa. The rarified alpha diversity in relation to the sampled area revealed decreasing values toward the deeper biotopes. However, similar rarified alpha diversities were found in all the biotopes in relation to the number of sampled individuals. Water depth, sediment grain size mode, CaCO₃%, and clay% were jointly correlated with faunal composition; water depth provided the single strongest correlate.