Larval bloom of the oviparous sponge Cliona viridis: coupling of larval abundance and adult distribution

We performed an intensive year-round sampling with the aim of studying the abundance of sponge larvae in four Mediterranean benthic communities: photo philic algae, sciaphilous algae, semi-obscure (i.e. low light-intensity) ca ves and sandy bottoms. We record here for the first time, a larval bloom of Cliona viridis (Schmidt 1862), the most common excavating sponge in the Me diterranean, which took place simultaneously in several rocky communities o f the Blanes sub-littoral (NE Spain), and discuss the role of restricted la rval dispersal in the distribution of adult sponges. In the communities stu died, C. viridis larvae bloomed synchronously once, in June. Spawning and c onsequent embryo development presumably occurred in May, when water tempera ture was 16 degreesC. The free larva is a small, evenly ciliated, weakly sw imming parenchymella with low dispersal capabilities. The number of larvae m(-3) and sponge abundance las percent cover and biomass) were significantl y higher in the community of sciaphilous algae than in the other communitie s studied. Because of limited larval dispersal, larval and adult abundance in the communities were positively correlated. Larvae developed into juveni le sponges 10 to 15 d after settlement. Settlers displayed distinctive feat ures: a peripheral cuticle, vacuolar etching-like cells at the sponge base, absence of oscular chimneys, and the presence of zooxanthellae, which were presumably transmitted during oocyte maturation.