Colonization dynamic on experimental limestone substrata. The role of encrusting epilithics favouring boring polychaetes

Polychaetes inhabit all the marine benthic communities and play a significant role in the degradation of calcareous substrates in marine environment. Colonization dynamics of encrusting epibenthos and polychaete assemblages on limestone experimental substrates were studied over a 3-year period in a Marine Protected Area: the Underwater Archaeological Park of Baiae (central Tyrrhenian Sea). Competitive and encrusting organisms replaced the pioneer species, dominating the epilithic community, and increasing the available surface. Polychaetes increased in species number over time. Several boring specimens of the species Polydora ciliata and Dodecaceria concharum were responsible for the bioerosion of the calcareous material. The former species characterized the early stage of the succession, whereas the latter settled during the late stages, together with the nestler species Lysidice unicornis, whose boring activity has been hypothesized. Four different surface trace morphologies attributable to boring polychaetes are here reported and described. The number of the polychaete boring traces increased according to the surface covered by ascidians, barnacles, and bryozoans. The present work provides evidence regarding positive interactions between encrusting epibenthic organisms and endolithic worms.