Reducing the data-deficiency of threatened European habitats: Spatial variation of sabellariid worm reefs and associated fauna in the Sicily Channel, Mediterranean Sea

Biogenic reefs, such as those produced by tube-dwelling polychaetes of the genus Sabellaria, are valuablemarine habitats which are a focus of protection according to European legislation. The achievement ofthis goal is potentially hindered by the lack of essential empirical data, especially in the MediterraneanSea. This study addresses some of the current knowledge gaps by quantifying and comparing multi-scalepatterns of abundance and distribution of two habitat-forming species (Sabellaria alveolata andS. spinulosa) and their associated fauna along 190 km of coast on the Italian side of the Sicily Channel.While the abundance of the two sabellariids and the total number of associated taxa did not differ at anyof the examined scales (from tens of centimetres to tens-100 of kilometres), the structure (compositionin terms of both the identity and the relative abundance of constituting taxa) of the associated fauna andthe abundance of several taxa (the polychaetes Eulalia ornata, Syllis pulvinata, S. garciai, Nereis splendidaand Arabella iricolor, and the amphipods Apolochus neapolitanus, Tethylembos viguieri and Caprellaacanthifera) varied among locations established ~50e100 km apart. Syllis pulvinata also showed significantvariation between sites (hundreds of metres apart), analogously to the other syllid polychaetesS. armillaris and S. gracilis, the nereidid polychaete Nereis rava, and the amphipod Gammaropsis ulrici. Thelargest variance of S. spinulosa, of the structure of the whole associated fauna and of 56% of taxa analysedindividually occurred at the scale of replicates (metres apart), while that of the dominant bio-constructorS. alveolata and of 25% of taxa occurred at the scale of sites. The remaining 19% and the total richness oftaxa showed the largest variance at the scale of locations. Present findings contribute to meet a crucialrequirement of any future effective protection strategy, i.e., identifying relevant scales of variation to beincluded in protection schemes aiming at preserving representative samples not only of target habitatsand organisms, but also of the processes driving such variability