Bio-Engineers of Marine Animal Forests: Serpulidae (Annelida) of the Biostalactite Fields in the Submarine Cave “lu Lampiùne” (Mediterranean Sea, Italy)

Marine caves are complex habitats characterized by intense environmental gradients from the entrance towards the innermost dark sectors. The submarine caves at the Cape of Otranto (Mediterranean, SE Italy) host skeletonized invertebrates able to build 3D structures by intermingling their hard body parts with microbial carbonates, thus acting as bio-constructors of true marine animal forests. Complex bio-constructions named “biostalactites” (BSTs) with a core of calcareous tubes of Protula sp. (Serpulidae, Annelida) have been recently found in the dark sector of the “lu Lampiùne” submarine cave, one of the most complex and largest in the area. In the present study, we examined the outer surface of a BST from “lu Lampiùne” in order to evaluate species richness, abundance and distribution of Serpulidae at proximal, intermediate, and distal positions along the BST and on the two opposite sides of the BST with different textures (coarse vs. smooth). The BST surface hosted 1252 specimens belonging to 9 Serpulidae species differently distributed along the BST and on differently textured surfaces. As expected, sciaphilic Serpulidae dominated in terms of number of species and individuals. Remarkably, the large Protula tubes of the BST core that allowed it to grow from 6000 years ago have been largely replaced by small-sized Serpulidae species. The present study contributes to increase the knowledge of the metazoans associated with biostalactite fields from “lu Lampiùne” cave and allows for a comparison with findings from other Mediterranean BSTs.