Seasonal reproduction in deep sea sponges - Triggered by vertical particle flux?

The examination of oogenesis and reproductive pattern in three deep-sea demosponge species from the foot of the Barents Sea continental slope (Norwegian Sea, similar to 2300 m, similar to 75 degrees 18'N; 9 degrees 55'E), Thenea abyssorum, Trichostemma sol and Tentorium semisuberities, suggests that sexual reproduction is triggered by the vertical flux of particulate organic carbon at least in one species. All three species examined reproduce sexually and proved to be oviparous and gonochoristic. A considerable number of asexually produced reproductive units was found in Thenea abyssorum, but owing to morphological details the origin of these buds is equivocal, and asexual reproduction is therefore judged to be of minor importance. Oogenesis in the three species can be divided into two developmental periods and does not differ greatly from processes known from shallow water species, except for the almost complete absence of nurse cells. For Thenea abyssorum a distinct seasonal reproductive cycle was found. The onset of yolk accumulation coincides precisely with a maximum in vertical particle flux as detected in sediment trap studies (von Bodungen et al. 1994). In addition, prior to yolk accumulation the sponge tissue appears almost ''empty'', without storage units. Once yolk accumulation (i.e. the second growth period) has started, gamete development and release are completed within a few weeks. Thus sexual reproduction is an important reproductive mode in deep-sea sponges, which may be triggered by the pulsed input of POC to this food-limited environment, the energy-dependent process of yolk accumulation being the most sensitive process.