title: The energetic cost of filtration by demosponges and their behavioural response to ambient currents.
abstract: Sponges (Porifera) are abundant in most marine and freshwater ecosystems, and as suspension feeders they play a crucial role in filtering the water column. Their active pumping enables them to filter up to 900 times their body volume of water per hour, recycling nutrients and coupling a pelagic food supply with benthic communities. Despite the ecological importance of sponge filter feeding, little is known about how sponges control the water flow through their canal system or how much energy it costs to filter the water. Sponges have long been considered textbook examples of animals that use current-induced flow. We provide evidence that suggests that some species of demosponge do not use current-induced flow; rather, they respond behaviourally to increased ambient currents by reducing the volume of water filtered. Using a morphometric model of the canal system, we also show that filter feeding may be more energetically costly than previously thought. Measurements of volumetric flow rates and oxygen removal in five species of demosponge show that pumping rates are variable within and between species, with the more oxygen consumed the greater the volume filtered. Together, these data suggest that sponges have active control over the volume of water they process, which may be an adaptation to reduce the energetic cost of filtration in times of high stress.
authors.affiliation: Department of Biological Sciences, University of Alberta, CW 405 Biological Sciences Building, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Danielle A
authors.initials: DA
authors.lastname: Ludeman
authors.affiliation: Department of Environmental Sciences, University of Virginia, 291 McCormick Rd, Clark Hall, Charlottesville, VA 22904, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Reidenbach
authors.affiliation: Department of Biological Sciences, University of Alberta, CW 405 Biological Sciences Building, Edmonton, Alberta T6G 2E9, Canada sleys@ualberta.ca.
authors.forename: Sally P
authors.identifier: 0000-0001-9268-2181
authors.initials: SP
authors.lastname: Leys
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D017753:Ecosystem; D004734:Energy Metabolism; D005374:Filtration; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D011161:Porifera / Q000033:anatomy & histology / Q000502:physiology* / Q000648:ultrastructure*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D010100:Oxygen
keywords: Current-induced flow; Energetic cost; Filter feeding; Oxygen; Passive flow; Porifera