SUSPENSION-FEEDING IN MARINE SPONGES HALICHONDRIA-PANICEA AND HALICLONA-URCEOLUS - EFFECTS OF TEMPERATURE ON FILTRATION-RATE AND ENERGY-COST OF PUMPING

Filtration rate (measured as clearance of algal cells) was measured at different temperatures in the sponge Halichondria panicea. An increase in water temperature from 6 to 12-degrees-C caused the mean filtration rate to increase 4.3 +/- 2.3 times. This value was higher than previously found for other marine ciliary suspension-feeding animals. Filtration rate at 12-degrees-C was also measured in Haliclona urceolus by means of an indirect clearance method in addition to a direct technique for measuring pumping rate. It was found that the 2 sponge species had near-identical filtration rates, with maximum rates of approximately 60 ml min-1 (g dry weight)-1 at 12-degrees-C. The normal pump pressure, or operating point O(p), of a standard sponge (based on our own measurements and calculations from literature data for a 0.1 g dry weight Haliclona sp.) was estimated as the sum of main contributions to head losses along the flow path from entry (ostia) to exit (osculum). The head losses were as follows: ostia 0.0373 mm H2O; inhalant canal 0.1205 to 0.013 mm H2O; prosopyles 0.1153 to 0.02321 mm H2O; collar-filter 0. 122 mm H2O; exhalant canals = inhalant canals; and osculum 0.1576 mm H2O. The (maximal) O(p) was found to be 0.673 mm H2O and the power output P(p) from the sponge pump was 0.677 muW. The pump work, defined as P(p)R-1 where R is the respiratory output, was 0.85 %. The low energy cost of filtration and the temperature effect are discussed and compared with recent data for other ciliary suspension feeders. It is argued that passive current-induced filtration may be of insignificant importance for sponges.