Hydroid and serpulid recruitment patterns using a new laser microtopography technique

Abstract The early settlement process is difficult to assess, due to the small size of the early settlers. Early recruitment counts generally concern individuals that have succeeded in taking the first step in this process, between the first larval contact with the substrate and the early growth of settled individuals. In this paper, a non-destructive technique is used to obtain information at organism level on the location and growth of freshly settled individuals. Settlement plates were collected every week for 2 months then replaced at sea. A video survey was combined with laser beam 3D surface analysis to obtain information on the individual location and size of settlers colonizing settlement panels immersed at two depths in western Mediterranean waters. Settling Pomatoceros (serpulid polychaete) were isolated with image analysis. Within hydroid colonies Clytia polyps were identified individually and their position stored on a database. Micro-topography was used to geo-localize settlers over time and thus identify inter-specific constraints during the settlement phase. Clytia colonies were seen to have a negative effect on the recruitment rate of Pomatoceros .