Spatio‐temporal Changes of Sabellarian Reefs Built by the Sedentary Polychaete Sabellaria alveolata (Linné)

Abstract

Abstract. Important intertidal sabellarian reefs are built by the polychaete Sabellaria alveolata (L INNÉ ) in the Mont Saint‐Michel Bay in Normandy at Champeaux (France). Typical profiles and plans were done over a ten year period. At the same time, population dynamics were examined during the last six years. At this site a nearly complete morphological cycle spread itself over more than ten years. Initially built on rock substrate (primary settlement phase), the studied reefs actually lie on a sandy shore. The growth phase begins by stages of balls which are then joined with new settlements between or on older tubes (secondary settlement). This phase comes to an end with an important platform stage. Then, the destruction phase brings us back to dead eroded reefs on which new worms can settle (secondary settlement). This cycle seems to be independent of the age of the living population, although new settlements of young worms and also sufficient hydrodynamics seem necessary.