Differences in reproductive timing among sponges sharing habitat and thermal regime

The reproductive cycles of four Mediterranean demosponges (Axinella damicornis, Corticium candelabrum, Raspaciona aculeata, and Chondrosia reniformis) were investigated during 2 consecutive years. Three of the species had annual gametogenic cycles characterized by a single peak of gamete production, but members of C. candelabrum showed continuous oocyte production during the 2 years. The relationship between gametogenic dynamics and seawater temperature varied substantially among species, contrary to the widespread belief that gamete production is associated with seasonal water warming. The annual temperature increase (in June) concurred with oocyte production only in C. reniformis, although maximum temperatures were simultaneous with the production of both oocytes in R. aculeata and sperm in C. reniformis. In contrast, the annual temperature decline in October was associated with both oogenesis in A. damicornis and spermatogenesis in R. aculeata. Spermatogenesis in A. damicornis started after a 5-month period of low-temperature values (December-April in 2004 and November-March in 2005). Likewise, in C. candelabrum, spermatogenesis started after a 3-month period of low-temperature values (November-February), a period concomitant with a slow increase in oocyte production. These findings reveal that sponge species that cooccur and share similar thermal regimes may differ substantially in their timing of gamete production. If we are to predict the future effects of climate change on marine benthic communities, there is an urgent need to improve our knowledge of the species-specific relationship between timing of gametogenesis and temperature, at least for those sponges that are key species in benthic communities.