Seasonal Variations of Spicule Size in Hymeniacidon Perleve

Abstract

Jørgensen (1944) showed that young specimens of the siliceous freshwater sponge Spongilla lacustris L. obtained their skeletal silica from the water and demonstrated that, under experimental conditions, a relationship existed between the size of the microscleric spicules produced and the concentration of dissolved silicate in the culture medium. The thickness of the microscleres increased with increasing concentration of dissolved silicate in the medium but no changes were detected in the lengths of the microscleres or in the size of the megascleres. Prior to this report Jewell (1935) showed that specimens of 5. lacustris with normal spiculation were rarely found in natural waters with a silicate content below 0.005 to 0.01 mm Si02. Hartman (1958) suggested that the greater thickness of siliceous spicules found in specimens of Haliclona caniculata Hartman collected in winter from New England shores, compared with spicules from summer-collected specimens, might reflect the increased concentration of dissolved silicate in the sea water during the winter months. Similar effects have been demonstrated experimentally in calcareous sponges: Maas (1906) showed that calcareous sponge larvae reared in calcium-free water produced no mineral spicules but organic ‘spiculoids’ of similar form. A relationship between spicule size and environmental silicate has not, in the past, been conclusively demonstrated for any siliceous sponge in field conditions.