Clearance rates and aquiferous systems in two sponges with contrasting life-history strategies

The clearance rates and microarchitecture of the aquiferous systems of two sympatric sponge species, Crambe crambe (Schmidt) and Dysidea avara (Schmidt), are compared. We performed a filtration experiment with fluorescent latex microspheres with diameters ranging from 0.2 to 4 mu m. Microsphere concentration in the water was measured by flow cytometry, and the particles ingested were detected within the sponge cells through confocal microscopy. The two species studied showed contrasting life-history strategies, reflected by different structural organizations of the aquiferous system, which in turn correlate with clearance rates measured in the filtration experiment. The species with higher growth and regeneration rates also showed the highest clearance rates at all particle sizes assayed and displayed larger ostia, a thicker choanosome layer, and larger flagellate chambers and choanocytes. The particle size most efficiently retained by both species was 1 mu m, and maximal clearance rates were obtained in all cases after 15 min of incubation. The sites of particle capture were the choanocytes, which retained small particles (0.2, 0.5, and 1 mu m) and, in the case of D. avara, also 4 mu m particles. The pinacocytes captured the largest particles assayed (6 mu m) and, in the case of C. crambe, also retained particles of the smaller sizes. It is concluded that there is an adaptive interspecific variation in structure and efficiency of the filtering systems in sponges which correlates with diverse biological strategies. The clearance rates obtained, coupled with the abundance of sponge populations in the community studied, point to a significant grazing impact of sponges on the picoplankton of the area. (C) 1997 Wiley-Liss, Inc.