INORGANIC SKELETON OF THE DEMOSPONGE HALICHONDRIA-PANICEA - SEASONALITY IN SPICULE PRODUCTION IN THE BALTIC SEA

Seasonality in spicule production of the demosponge Halichondria panic ea (Pallas, 1766) was studied in the Western Baltic from July 1992 to July 1993. Spicule production increased in parallel with increasing te mperatures in spring, being most pronounced during summer after releas e of larvae. Large proportions of up to 30% immature spicules occurred in the population during skeleton production peaks, and this resulted in reduction of mean spicule dimensions by similar or equal to 20%. E ffects on spicule width were more obvious than on spicule length. In w inter, when wave forces were largest, higher percentages of mineral sk eleton were observed: 50% of dry weight compared to 40% in summer. Enh anced spicule densities in the tissues were not attained by marked spi cule production but through a reduction in organic content by shrinkin g. In spring, growth of body tissue was faster than the build-up of sk eleton, so that the relative amount of the latter was reduced. The ind irect, growth-related developments of the skeleton were inversely prop ortional to temperature and directly to salinity, silicate concentrati ons and wave energy. Spicule size and the number of immature spicules were correlated with temperature and only slightly with salinity. No c orrelation with oxygen concentration or pH could be detected.