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Data associated with Matveev et al: Sense Induced Flow - Active use of ambient flow by a deep-sea glass sponge

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  • How flow moves through porous structures like sponges is a fluid dynamic problem that has challenged physical and biological scientists. Sponges possess biological pump cells that are known to drive water flow, and yet their porous bodies have often been proposed to take advantage of ambient currents passively. Here we focus on the ‘induced-flow’ theory which proposes that pipe-shaped structures can allow flow external to the tube to drive flow through the tube. This concept has been widely applied to both living systems and biogenic structures and particularly resonates with paleontologists who often give a poriferan-affinity to fossils with holes, assuming that the canals of sponges are inert. A modern understanding of sponge morphology and physiology however, shows sponges possess a sophisticated sensory system, even in the canals. Glass sponges (Hexactinellida) are an ideal group with which to re-examine the hypothesis because individuals have large oscula and have a well-studied sensory system that can cause feeding current arrests. Here we studied filtration and metabolism from glass sponges in their natural habitat on a glass sponge reef at 190m depth. We used custom oxygen and flow sensors to record oxygen removed per liter pumped over several tidal cycles, to test the hypothesis that the glass sponge Aphrocallistes vastus expends less energy to filter more water during higher ambient flow. We found that more water was filtered during periods of higher ambient current in only one of six individuals. However, all sponges arrested pumping independently of ambient currents, indicating they have control over pumping. We compared oxygen removal between low and high ambient flow during periods when sponges were pumping (high excurrent). Surprisingly, four of six sponges removed on average 30% less oxygen when the ambient current was high. This suggests a mechanism by which the sponge senses the increase in ambient flow rates and reduces the cost of filtration. The underlying mechanism by which the sponges sense the change in ambient current and control the flow through its body remains unknown, but may involve feedback from primary cilia at the osculum that are involved in flow sensing and dilation of canals in other sponges. Our experiments show that while sponges can take advantage of current-induced flow, the flow through these animals is controlled by their complex physiology. Overall these results imply that the feedback system in nerveless sponges functions in a manner similar to other animals formed by tubes.

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    Attribution-NonCommercial 4.0 International