THE REPRODUCTIVE-CYCLE OF THE SPONGE HALICHONDRIA-PANICEA PALLAS (1766) AND ITS RELATIONSHIP TO TEMPERATURE AND SALINITY

The reproductive cycle of the sponge Halichondria panicea was investig ated at Boknis Eck in the Western Kiel Bight over 2 yr, and over 1 yr on the island Helgoland in the North Sea and was compared with materia l collected earlier at Tjarno at the Swedish west coast. Temperature a nd salinity were monitored at the different stations in order to deter mine whether different hydrographic conditions could be linked to diff erences in seasonal patterns of the reproductive cycle. The results sh owed H. panicea to be gonochoristic at all stations. The ratio of male s to females varied between populations and years, but females predomi nated consistently. Comparison of the reproductive cycle in the years 1987 and 1989 at the brackish-water station Boknis Eck shows that high ambient winter and spring temperatures in 1989 resulted in a shorter period of oogenesis and earlier larval release, as compared to the yea r 1987. The reproductive cycle of the sponges at the fully marine stat ion at Helgoland in 1989 and the brackish-water station at Tjarno in 1 978 under temperature and salinity conditions similar to those at Bokn is Eck in 1989 showed the same seasonal pattern. We conclude that the lower salinities found at both Boknis Eck and Tjarno do not cause a de lay or slow-down of reproduction at these stations as compared to Helg oland. Under favourable temperature conditions, oogenesis was highly s ynchronous within the different populations, while it was more spread over time under the low ambient water temperatures at Boknis Eck in 19 87.