17.2 Wednesday, Jan. 4 The sponge pump: the role of current induced flow in the design of the sponge body plan LEYS, SP*; YAHEL, G; REIDENBACH, M; TUNNICLIFFE, V; SHAVIT, U; REISWIG, HM; University of Alberta; Ruppin Academic Centre; University of Virginia; University of Victoria; Israel Institute of Technology; University of Victoria email@example.com
Sponges are suspension feeders known to actively filter a volume of water equivalent to many times their body volume of water per hour, using flagellated collar-cells (choanocytes). Flow through sponges is thought to be enhanced by ambient current which induces a pressure gradient across the sponge wall. Studies of sponge filtration have estimated the energetic cost of pumping to be < 1 % of its total metabolism implying there is little adaptive value to reducing the cost of pumping by using “passive” flow. We quantified the pumping activity and respiration of the glass sponge Aphrocallistes vastus in situ at a 150 m deep reef and in a flow flume; we also modeled the glass sponge filtration system from measurements of the aquiferous system. Excurrent flow from the sponge osculum measured in situ and in the flume were positively correlated (r>0.75) with the ambient current velocity. During short bursts of high ambient current the sponges filtered two-thirds of the total volume of water they processed daily. Our model indicates that the head loss (due to resistance) across the sponge collar filter is 10 times higher than previously estimated across the demosponge collar. The difference is due to the resistance created by a fine protein mesh that lines the collar, which demosponges also have, but which was not included in previous measurements. These pumping rates give a conservative energetic expenditure of ~60 mJ (L pumped)-1, at least 25% of the total in situ respiration. We suggest that due to the high cost of pumping, current induced flow is highly beneficial for tall, thin walled sponges living in high flow environments. Our results call for a new look at the cost of biological pumping and its evolutionary role, especially in sponges.