Serpula aggregates and their role in deep-sea coral communities in the southern Adriatic Sea

We document a remarkable abundance of thetubeworm Serpula vermicularis Linnaeus, 1767, in bathyalcoral habitats from the Bari Canyon System in the southernAdriatic Sea. Here, the specimens of S. vermicularis growfrom muddy substrate either as isolated individuals or aslocalized clusters of multiple individuals. Peculiar tubeaggregations are also associated with Madrepora oculatabuild-ups and other stony corals including Desmophyllumdianthus. Three types of coral-serpulid (C–S) frameworkshave been recognized based upon size and shape. Theabundance of S. vermicularis increases with the size ofC–S frameworks, which results from superimposition,overgrowth, and/or intergrowth of scleractinians and serpulids.Several generations of S. vermicularis contribute tothe C–S frameworks, each most probably accounting formore than 8 years and presumably existing in the area forthe last hundreds of years. At a meso-scale, the distributionpattern of serpulids seems to be mainly governed by currentsand siltation. A further constraint is the co-occurringsolitary coral D. dianthus within frameworks. The successfulsea-bottom colonization by S. vermicularis andassociated C–S frameworks is possibly related to a highoxygen content and food supply derived from the NorthAdriatic Dense Water (NAdDW). The flourishing populationsof S. vermicularis as well as the peculiarity of C–Sframeworks suggest that deep-sea canyons provideimportant benthic habitats in bathyal environments.