Sponge fauna associated with mesophotic invertebrate bioconstructions along the Apulian coasts (southern Italy, central Mediterranean)

This study characterizes the sponge fauna associated with mesophotic invertebrate bioconstructions along the Apulian coasts (southern Italy), providing new insights into their taxonomic composition and distribution. Through image analysis, taxonomic identification and morphological assessments, we identified a rich sponge assemblage inhabiting mesophotic invertebrate bioconstructions built by corals (MCB) and oysters (MOB) at depths between 40 and 65 m. Of a total of 140 Porifera taxa identified, 27 species were exclusive to MCB and 46 to MOB, and 47 were found in both bioconstructions. Although α-diversity did not differ significantly between bioconstruction types, with 74 species recorded at MCB and 93 at MOB, coverage values were lower for MCB than for MOB (20.5% ± 1.91 vs. 32.3% ± 3.1). Sponge assemblages were dominated by massive growth forms (78%), followed by encrusting (13.7%) and erect (7.7%) morphologies, with Aplysina cavernicola and Keratosa showing the highest median coverage. These findings highlight the importance of mesophotic invertebrate bioconstructions as biodiversity hotspots and underscore the role of sponges as key habitat engineer organisms, emphasizing the need for their inclusion in conservation and monitoring frameworks.