The influence of habitat complexity on fish assemblages associated with extractive platforms in the central Mediterranean Sea

In this work the influence of habitat complexity on fish assemblages associated with extractive platforms in the Mediterranean Sea was investigated. More specifically, at large spatial scale we tested the differences in fish assemblage between 4-legs vs 8-legs platforms, whereas at medium scale we evaluated, within each platform, the differences between internal structures with increasing complexity degrees (respectively: the water volume without any pillar - complexity “0”; the junction of two pillars - “1”; the junction of four pillars - “2”). Both univariate and multivariate analyses showed highly significant differences for each of the tested factors, as well as for their interaction. In general, at both medium and large spatial scales, mean species richness and abundance were positively correlated with the increasing habitat complexity with the highest values associated with 8-legs platforms and with the most complex internal structures within each platform. According to our findings, a more complex structure is able to attract more fish species and specimens than a less complex one, supporting previous studies carried out on different man-made structures outside the Mediterranean Sea. The study will integrate the still poor available knowledge baseline on the attractive potential of extractive platforms with strong implications for the environmental management under the incoming light of decommission in the basin.