Polychaetes as Habitat Former: Structure and Function

Polychaetes are one of the highest diversified group of invertebrates, playing a significant role in the functioning of benthic communities. They have colonized every marine environment, they reach high density in various seabed habitats and show a wide range of morphological and feeding habit diversity. Many species are able to create primary biogenic structures that offer new substrates for other benthic species, or to modify the abiotic characteristics of the pre-existing substrate both on rocky and on soft bottoms. A large number of polychaetes consists of sessile and tube-dwelling forms, often gregarious, which act as real bioconstructors, playing the role of both primary and secondary frame builders. Also in soft-bottoms some species are able to create biogenic, forest-like structures which affect habitat conditions and regulate ecosystem functioning. Thus, polychaetes are ascribed to the engineers of animal forests. In this paper the main evidences of polychaetes as ecosystem engineers are synthetically reported highlighting their ecological role as habitat formers; the time-scale variations of the biogenic structures are considered and the sensitivity and threats of polychaete forests are exhibited in the light to sustainable management measures and protection of marine coastal ecosystems.