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Abstract. The major in situ physiological activities of the common, tropical, West Atlantic demosponge Verongia (=Aplysina) fistularis were determined in order to relate the carbon and energy budgets of this species to the two contrasting patterns documented for bacteriosponges (sponges harbouring large symbiotic bacterial populations) and non‐bacteriosponges (sponges lacking such large bacterial populations and considered “normal” sponges). Measurements of specimen dimensions and exhalant water velocity, and samples of exhalant water were obtained from undisturbed field specimens for estimation of rates of water transport, respiration and particulate organic carbon retention. Partial carbon and energy budgets were developed from calculated rates of particulate feeding, respiration and growth. The bacteriosponge, V. fistularis, is very similar to Verongula sp., another bacteriosponge, in terms of high respiration rate, 5.33% of available oxygen being removed during a single‐pass water transit, and gross imbalance in particulate carbon and energy budgets, particulate sources supplying only 14% of respiration and growth requirements. The nutrient resource spectrum of Verongia fistularis and other bacteriosponges appears to be overwhelmingly dominated by dissolved organic matter, and thus contrasts strikingly with the present knowledge of nutrition in the normal non‐bacteriosponges.

Sponges are suspension feeders that use flagellated collar-cells (choanocytes) to actively filter a volume of water equivalent to many times their body volume each hour. Flow through sponges is thought to be enhanced by ambient current, which induces a pressure gradient across the sponge wall, but the underlying mechanism is still unknown. 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 induced by the ambient current. We quantified the pumping activity and respiration of the glass sponge Aphrocallistes vastus at a 150 m deep reef in situ 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 across the sponge collar filter is 10 times higher than previously estimated. The difference is due to the resistance created by a fine protein mesh that lines the collar, which demosponges also have, but was so far overlooked. Applying our model to the in situ measurements indicates that even modest pumping rates require an energetic expenditure of at least 28% of the total in situ respiration. We suggest that due to the high cost of pumping, current-induced flow is highly beneficial but may occur only in thin walled sponges living in high flow environments. Our results call for a new look at the mechanisms underlying current-induced flow and for reevaluation of the cost of biological pumping and its evolutionary role, especially in sponges.

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Glass sponges are conspicuous inhabitants of benthic communities in the cool waters of the Antarctic and north Pacific continental shelf. We used an ROV outfitted with a new device for simultaneous sampling of water inhaled and exhaled by the sponges to provide the first data on the nutritional ecology and metabolism of two glass sponge species in their natural deep-water habitat (120-160 m). Aphrocallistes vastus and Rhabdocalyptus dawsoni were found to be mostly bacteriovores, removing up to 95% of the bacteria (median removal was 79% for both species) and heterotrophic protists (,10 mm) from the water they filter. The relatively scarce microbial cells were efficiently selected from a 'soup' of suspended clay and detritus particles (microorganisms accounted for ,1% of the total ambient suspended solids). Removal of planktonic microorganisms (2.2 6 1.3 mmol carbon [C] C L 21 and 0.37 6 0.17 mmol nitrogen [N] L 21 ) accounted for the entire total organic C uptake and ammonium excretion by both species, with no evidence for dissolved organic uptake. Similar results were obtained in laboratory experiments in which dissolved organic C was directly measured. Despite the massive siliceous sponge skeleton, silica uptake was below detection levels (0.28 mmol L 21 ), supporting previous suggestions of low growth rates in Hexactinellida. Reported mean sponge abundances of .1 individual m 22 indicate that the sponge filtering activity may significantly affect the deep microbial community and benthic-pelagic mass exchange in some northeast Pacific fjords.Shallow-water benthic suspension feeders have an important role in the functioning of coastal and freshwater ecosystems (Gili and Coma 1998;Thorp and Casper 2003). The feeding activity of these animals can control the water column properties in shallow bays (Cloern 1982), rivers (Strayer et al. 1999), and fjords (Riisgå rd 1998), either directly (through grazing on the plankton community) or indirectly (by intensifying nutrient recycling or by selective removal of a specific planktonic component) (Thorp and Casper 2003). These activities are tightly coupled with hydrodynamic processes.Whereas the nutritional ecology of shallow suspension feeders has been well studied, equivalent studies of the nutritional ecology of deep-dwelling suspension feeders (below scuba depth) are scarce (Roberts and Hirshfield 2004) and rely largely on descriptive anatomy and in vitro experiments (e.g., Fiala-Medioni et al. 1986;Witte et al. 1997; Pile and Young 1999

Samples of ambient aquarium water (inhalant) and oscular stream (exhalant) of the sponges Haliclona permollis (Bowerbank) and Suberites ficus (Johnston) were analyzed for bacteria by three methods. Bacterial removal efficiencies were 70.3 and 77% from plate cultures, 44 and 68% from surface fouling, and 77% from direct filter counting in a single transit of the sponge filter. Bacteria alone can satisfy the entire food requirements for these sponges. Bactericidal activity is not expressed in exhalant water samples. If bacterial toxins are produced by these sponges, their activity must be restricted to local sites within the confines of the organisms.