ENVIRONMENTAL INSTABILITY AND DEMOGRAPHIC VARIABILITY IN ACROCNIDA-BRACHIATA (ECHINODERMATA, OPHIUROIDEA) IN DOUARNENEZ BAY (BRITTANY - FRANCE)

The recruitment and growth modalities of two populations of Acrocnida brachiata (Echinodermata:Ophiuroidea) from the intertidal and from a depth of 20 m in Douarnenez Bay (Brittany) were compared. This study was conducted in order to establish whether the populations developed differently according to environmental stability. The results were compared with those found in another amphiurid, Amphiura filiformis, distributed along a similar gradient of disturbance in the subtidal zone. The purpose was to determine whether the biological parameters from different species vary in a similar manner along such a gradient and, if not, what is the role of biotic and physical factors in the control of demographic structure in intertidal and subtidal populations.