SILICA UPTAKE KINETICS OF HALICHONDRIA-PANICEA IN KIEL BIGHT

Besides diatoms Demospongiae are the most important consumers of disso lved silica in the sea. They can play an important role for the silica budget especially in the shallow water areas of the Baltic Sea. The d ependence of the silica uptake rate on the silica concentration of the seawater was measured for the sponge Halichondria panicea (Pallas, 17 66). The sponges were collected in Kiel Eight. The uptake conformed to Michaelis-Menten kinetics with a half-saturation constant of 46.41 mu M and a saturated uptake rate of 19.33 mu mol h(-1) g(-1) (p < 0.01). In the red algae zone of Kiel Eight the sponges depend on silica supp ly from the surrounding waters and map be silica-limited rather than f ood-limited in growth. Because of the much faster uptake of silica by diatoms and their lower saturation point, as well as the difference in spatial distribution of the two main silica consumers, a competition for silica between sponges and diatoms seems unlikely.