Sponge explants were placed onto mesh racks 5 cm above the bottom of the tank and circulation was maintained within the oval tank by four power head pumps (Aquaclear 702). Each aquarium was illuminated on a 10:14 h light:dark regime. Surface-associated fouling organisms were carefully removed from the surfaces of all individuals to ensure that the respiration rates measured were only those of the sponge and its associated micro-organisms.