Biogeomorphology of Phragmatopoma lapidosa Kinberg, 1867 reef formations of São Paulo State rocky coasts (Brazil).
Résumé
The polychaetous annelids of Sabellariidae family construct their tubes by means of an agglomeration of sandy particles. Two species are known to build significant bioconstructions, named reefs or bioherms, consisting of juxtaposed tubes : the temperate European species Sabellaria alveolata (Linnaeus, 1757) and the tropical and sub-tropical American species Phragmatopoma lapidosa Kinberg, 1867 (=P. Caudata Kirtley, 1994). P. Lapidosa distribution is reported from the Florida's coast to the southern coasts of Brazil. They both constitute consolidated mounds of various shape and size. In Brazil, the bioconstructions built are less developed than the real reefs of Florida or by the European species. The formations look like ridges and benches or sheet-like reefs. The São Paulo State reefs are a quite interesting area because P. lapidosa have colonized the entire lower intertidal zone of the exposed rocky shore. During high tide, P. lapidosa can collect through the flared and open ends of their tubes, the requisite sand-size particles for tube construction. The tubes consist entirely of sand-size particles bound together by organic cement which was analysed by Electron Microscopy and X Microanalysis. The grain-size distribution of the tubes and the surrounding sediments was carried out with Laser Granulometer technique. The horizontal and vertical growth of the reefs is controlled by biological factor, hydrodynamic conditions, and the availability of sandy particles. These bioconstructions present various forms which are modelled according to their wave exposure.