SILICA UPTAKE OF THE MARINE SPONGE HALICHONDRIA-PANICEA IN KIEL BIGHT

The silica uptake of Halichondria panicea Pallas, 1766 was measured in laboratory experiments from February until August 1995. Uptake rates were determined by measuring the decrease of dissolved silica in the s urrounding seawater. All specimens were collected in Kiel Bight and ma intained in aquaria up to several weeks prior to the experiments. Up t o 5.27 mu mol Si g(-1) AFDW h(-1) were incorporated by the sponges, wi th a strong, size-independent individual variation. A positive correla tion between the content of dissolved silica in the seawater and the s ilica uptake was found. Temperature had no decisive effect on uptake r ates. The nutritional condition of the sponges turned out to be of gre at importance. After 1 wk of starvation, Halicondria panicea uptake ra tes were only 15% of the previous amount, which indicates that silica transport is an energy-consuming process. During the most intense phas e of reproduction activity in spring, female specimens showed a signif icant drop in their silica uptake. Obviously they did not produce spic ules during this time. An attempt to estimate the influence of H. pani cea on its habitat as a consumer of dissolved silica led to the conclu sion that in summer the sponges might affect the phytoplankton species composition by competing with diatoms for dissolved silica.