PEARSON, GARETH A*; SERRAO, ESTER A; Universidade do Algarve; Universidade do Algarve: REVISITING SYNCHRONOUS SPAWNING IN SEAWEEDS � IS IT JUST ABOUT SEX?

External fertilization is common in the marine environment. However, in the intertidal zone the prevailing hydrodynamic conditions may reduce the effectiveness of external fertilization as a reproductive strategy by dilution of the gametes. Fucoid algae overcome this problem by synchronizing gamete release to occur during periods of low water motion. We review our current understanding of the mechanisms controlling gamete release, which include inorganic carbon sensing (water motion proxy), as well as light quality photoreception (a putative depth sensor). The importance of synchronous gamete release in natural populations is predicted to vary with mating system; i.e., highly important for obligate outcrossing species, and less so for self-compatible species. However, long-term data sets for gamete release in natural populations of dioecious and hermaphroditic cogeners (Fucus vesiculosus and F. spiralis) indicate that patterns of release and levels of synchrony are very similar, independent of mating system (obligate outcrossing and largely selfing, respectively). The occurrence of synchronous gamete release in species with high rates of self-fertilization may indicate that fertilization success is not the only selection pressure operating on the trait. Specifically, synchronous release and fertilization under calm conditions may be equally important in reducing dispersal (and therefore zygote wastage) in intertidal organisms with restricted vertical distributions.