Osculum dynamics and filtration activity in small single-osculum explants of the demosponge Halichondria panicea

Abstract

Contraction-inflation behavior, including the closure and opening of the exhalant opening (osculum), is common among sponges. This behavior may temporally affect filtration activity, making it difficult to study and understand sponge feeding biology. To examine the interplay between osculum dynamics and filtration activity, small (18 mm3) single-osculum explants of the demosponge Halichondria panicea were studied. Time-lapse video stereo-microscope recordings of the osculum cross-sectional area (OSA) were made simultaneously with measurements of the filtration rate (∼15°C, ∼20 PSU) using the clearance method. Osculum dynamics, as expressed by temporal variation of the OSA, including osculum contraction and expansion, correlated with variability in the explant filtration rate, and no water pumping was observed during periods of osculum closure. A linear relationship between filtration rate (FR) and OSA revealed a constant exhalant jet velocity: vjet = FR/OSA = 2.3 ± CI95% 0.13 cm s-1. The mean filtration rate of explants was 0.28 ± CI95% 0.06 ml min-1, corresponding to a volume-specific filtration rate of 15 ml min-1 (cm3 sponge)-1, which is 2 to 3 times higher than that reported for larger individuals of H. panicea with multiple oscula. This is the first demonstration of a direct relationship between filter feeding and osculum dynamics in a sponge.