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 mm 3 ) 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: v jet = FR/OSA = 2.3 ± CI 95% 0.13 cm s , 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.
Sponges pump large amounts of seawater through their water canal system, providing both food and oxygen to the sponge body. Sponge pumping activity may show considerable variation as a consequence of contractile behavior, which includes contraction and expansion of the exhalant opening (osculum) in regular or irregular time intervals. The present study unravels short-and long-term effects of contractionexpansion events on the respiration rate of small single-osculum explants of the demosponge Halichondria panicea. Based on simultaneous video-microscopic timelapse recordings of osculum cross-sectional area (OSA) and projected area (A), combined with respiration rate measurements, we further evaluate the role of pumping activity for oxygen uptake in the explants. Pumping dynamics were expressed by cyclic contraction-expansion events of the OSA and A, including osculum closure with a mean duration of 37.5 ± CI 95% 13.7 min. The respiration rate of sponge explants remained relatively constant at 0.046 ± CI 95% 0.014 µmol O 2 h −1 (i.e., 7.41 µmol O 2 h −1 g −1 DW sponge) during contraction-expansion cycles, but with a marginal decrease of 9.6% during osculum closure. Periods of pumping cessation during osculum closure likely caused reduced oxygen levels in the sponge body, increasing the oxygen gradient between the environment and the sponge interior, allowing enhanced diffusion of oxygen across the explant surface. This is a key mechanism for balancing respiratory demands during sponge contractions. While contractile behavior is only marginally associated with decreased respiratory demands in small single-osculum H. panicea explants, it may control the degree of internal oxygen depletion and thereby ensure maintenance of sponge-associated microorganisms during non-pumping periods.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.