Despite their abundance in benthic ecosystems, life cycles and reproductive features of most sponge species remain unknown. We have studied the main reproductive features of two demosponges, Dysidea avara and Phorbas tenacior, belonging to phylogenetically distant groups: Orders Dictyoceratida and Poecilosclerida, respectively. Both sponges are abundant and share habitat in the Mediterranean rocky sublittoral. They brood parenchymella larvae with different morphology and behaviour. Sampling was conducted monthly over a two-year period in a locality where both species coexist. The two species reproduced in spring-summer, and presented species-specific reproductive features despite being subject to the same environmental conditions. D. avara has a shorter reproductive period than P. tenacior, ending before the peak of temperature in summer, while the reproductive period of P. tenacior lasts until beginning of autumn. Brooding larvae were present in June-July in D. avara, and in August-October in P. tenacior. Larval size, reproductive effort and number of larvae produced (measured the month with the maximum production) were significantly higher in D. avara than in P. tenacior. A higher reproductive effort and larval traits point to a more opportunistic life strategy in D. avara than in P. tenacior. A lack of overlap in the timing of larval release, as well as different reproductive traits, may reduce competition and facilitate the coexistence of these two sympatric and abundant sponges.
Keywords: Larvae; Marine invertebrates; Mediterranean sea; Reproduction; Sponges.