Sexual reproduction of Geodia barretti Bowerbank, 1858 (Porifera, Astrophorida) in two Scandinavian fjords

The gametogenesis in the common cold-water sponge Geodia barretti is described from two Scandinavian fjords through a year cycle: in Korsfjorden, western Norway, and in Kosterfjorden on the Swedish west-coast. The reproductive cycle is annual for both populations, with one or two periods of gamete release per year. Individuals within the same local population reproduce simultaneously within a restricted period of time. Geodia barretti is a dioecious and oviparous sponge, with oocytes (up to 100 μm in diameter) and spermatic cysts (up to 125 μm in diameter) organised in clusters within the mesohyl. The sponge has asynchronous spermatogenesis and synchronous oogenesis. Asexual reproduction has not been observed. The onset of the reproduction coincides with the phytoplankton blooms in both fjords: Gametes are released in early summer, just after the phytoplankton spring bloom is over. In Kosterfjorden, however, an additional release of gametes occurs in October, just after the autumn phytoplankton bloom. In both fjord systems reproduction of G. barretti thus matches the peaks in sedimentation of organic matter that follow after phytoplankton blooms