Serpulid diversity of coralligenous build-ups in the southwestern Ionian Sea

Coralligenous build-ups in the Ionian Sea off southeastern Sicily, Italy, first discovered about 20 years ago, were recently studied as part of the Italian FISR project ‘CresciBluReef’. Coralligenous build-ups are a priority habitat in the Mediterranean Sea, yet their origin and species richness are still poorly known. In the studied area, calcareous algae constitute the primary framework of the concretions, and serpulid worms and other invertebrates contribute secondarily. Live and dead serpulid associations were sampled from four build-ups at a depth of 33–37 m. Thirty-five living species of Serpulidae were detected (12 Serpulinae, 15 Filograninae and 8 Spirorbinae), some of which were frequent and abundant. This greatly outnumbers the 7 species previously found at a single build-up in the same area, and the 10 species reported from nearby coralligenous concretions. All but two of the species were already known from the Mediterranean Sea, although eight of the species (three of which are still under description) are reported for the first time from the coralligenous biocoenosis. Our findings highlight that: (i) the serpulid species richness of the studied build-ups is higher than that known in other Mediterranean areas; (ii) the serpulid associations at the four build-ups are comparable in composition and structure, except for a slight reduction in numbers of individuals with depth; and (iii) at each build-up, serpulids are more abundant in the top part than in the bottom part of the concretions.