A 3-year investigation of sexual reproduction in Geodia cydonium (Jameson 1811) (Porifera, Demospongiae) from a semi-enclosed Mediterranean bay

Abstract

The reproductive cycle of Geodia cydonium in a semi-enclosed Mediterranean bay (Porto Cesareo, SW Apulia) was studied with monthly frequency over a 3-year period. The investigation was carried out by uti- lizing a technique consisting of tagging ten individuals with a PVC stick and cutting oV, by means of a metal cork borer, small samples (cylinders about 5 cm 3 in vol- ume) from each of them for histological analysis. Sex- ual reproductive elements were detected in all individuals, but in the third year some specimens showed reduced reproductive activity or complete infertility. Spermatogenesis occurred in a short period (from June to August) whereas oogenesis lasted longer (from spring to late summer). Spermatic cysts occurred when the frequency of specimens with oocytes reached its maximum values. A relationship between water temperature and the onset of gamete diVerentiation was observed. G. cydonium is here conWrmed ovipa- rous and gonochoric with a sex ratio in favour of the females. However, in contrast with current literature on Porifera—which suggests that only a limited num- ber of sponges, all belonging to the same species are sexually active—the sexual reproduction of this species involves all the examined individuals. This Wnding can be explained by the methodological approach used in this research, which diVers from the traditional way of assessing the sponge reproductive cycle by analysing randomly collected specimens within a population. The study of a series of individuals over time represents a better "model technique" for investigating sponge sex- ual reproduction and the eVect of environmental parameters on gamete diVerentiation.