Recruitment, habitat selection and larval photoresponse of Paraleucilla magna (Porifera, Calcarea) in Rio de Janeiro, Brazil

Little is known about the recruitment and behaviour of sponge larvae, especially of the class Calcarea. The calcareous sponge Paraleucilla magna is very common in Southeast Brazil, where it is considered a cryptogenic species. This study quantified recruitment rates in shaded and illuminated habitats for 2years in Rio de Janeiro, Brazil, and analyzed larval photoresponses of this species. Four structures, each containing a shaded and an illuminated surface, were exchanged every 3months for 2years. The number of recruits was quantified on each plate. In the laboratory, larvae of P.magna were placed in half-shaded Petri dishes and the number of settlers in each side was counted after 24h. Paraleucilla magna recruited continuously throughout the experiment. Recruits occurred in greater abundance on shaded surfaces than on illuminated surfaces, and the larvae were negatively phototactic in vitro. Despite the possible influence of other factors in the recruitment of sponges (such as sedimentation, competition and predation), the prevalence of P.magna in shaded habitats may also be related to larval choice.