Testing passive flow and oxygen consumption in three temperate demosponges

Meeting Abstract

116.10  Monday, Jan. 7  Testing passive flow and oxygen consumption in three temperate demosponges LUDEMAN, DA*; REIDENBACH, MA; LEYS, SP; University of Alberta; University of Virginia; University of Alberta sleys@ualberta.ca

Sponges are suspension feeders that process up to 900x their body volume in water daily, and extract bacteria with up to 98% efficiency. Because of their small incurrent openings and larger excurrent vents, sponges have long been considered to take advantage of passive flow to reduce the cost of pumping for filtration. But it is unclear whether all sponges a) need to use passive flow, and b) are able to use passive flow. Deep-water glass sponges live in nutrient-poor waters, and are found mainly in areas of constant high ambient flow. The cost of pumping (resistance through their filtration system) for glass sponges has been found to be nearly 30% of their metabolism, and the expense of pumping is reduced by taking advantage of current induced flow. Demosponges have much finer canal systems which should provide higher resistance than in glass sponges. We predict that passive flow does not occur in these sponges, but instead their food-rich temperate waters provide enough energy to sustain maintenance and growth despite the high cost of pumping. To determine this we studied excurrent filtration rates and oxygen consumption during ambient flows of 0-18cm/s in three temperate demosponges using particle imaging velocimetry, profiling acoustic Doppler velocimeters, and an oxygen optode. We found that excurrent velocities varied among the three demosponges, but none increased with increasing ambient flow. Oxygen drawdown was similar for all three sponges (0.1-0.4 mg/mL) and also did not increase with increased ambient flow, meaning no additional energy was expended to pump during increased ambient flow. Morphometric analysis of the aquiferous system will be used to model whether increased ambient currents can induce excurrent flows.

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