Current-induced flow through living sponges in nature.

Abstract

Flow velocities through and immediately adjacent to the excurrent openings (oscula) were measured in eight species of marine sponges in their natural environments with a two-channel thermistor flowmeter. Flow through the oscula was positively correlated with both normal and artificially augmented ambient flow in both normally pumping and inactive animals. These results indicate that the passage of water through these sponges is, in part, induced by ambient currents.As a consequence of any of several physical mechanisms, internal flow through a structure may be induced by the flow of an external medium across that structure. Consider, for example, a fixed tube open at both ends exposed to a moving fluid. Flow through the tube may be driven by the increased pressure at an upstream-facing opening, by the reduced pressure at an elevated aperture with its axis normal to the external current (both according to Bernoulli's equation), and by the reduced pressure due to viscous entrainment at any opening normal to the external current. (1, 2).Organisms may take advantage of this phenomenon to induce flows through themselves or their domiciles. Of the various groups of organisms that might do so, the sponges constitute the most inclusive taxonomic category. Most of the members of the entire phylum seem morphologically and ecologically appropriate: these sedentary animals commonly filter-feed in moving water, with fluid entering tiny pores in their walls and leaving through much larger openings usually well-removed from the substratum. Flagellated cells within the sponges are demonstrably capable of driving substantial filtration currents; the present question concerns the existence of flow induced by the external medium and its magnitude relative to actively pumped flow.The suggestion that some of the flow through sponges might be a passive consequence of ambient currents was based on observations on physical models (1), and current-induced flow could also be demonstrated on living sponges in a laboratory flow tank (3). However, steady flow in a tank, while permitting straightforward comparisons with models, is far from the situation encountered by a sponge in nature; furthermore, the animals that actively pumped water in a tank did so at rates substantially lower than those expected in the field. The applicability of the laboratory observations to sponges in their natural environment has therefore been questioned (4).I now report the results of recordings of the flow of seawater through and immediately adjacent to living sponges in their normal habitats. The pumping activities of the present animals range up to an order of magnitude above those previously examined in the laboratory. Nonetheless, the correlation between ambient current and flow through the sponges is still evident. Artificial increases in ambient flow are associated with increased flow through the animals, and inactivated sponges show the same purely passive internal flow as previously observed. MATERIALS AND METHODSMeasurements were made in situ ...

Environmental Flow Regimes for Dysidea avara Sponges

“…They possessed the tallest protuberances with the largest terminal oscula. Their shape is correlated with the generally low flows found within their protected minicave habitat and is supported by the concept that oscula placed high on protuberances help insure maximum separation of ejected metabolic wastes and new oxygenated water and food particles entering the ostia at the surface of the sponge (Vogel 1977(Vogel , 1994.…”

“…From published studies on sponge fluid mechanics (Riisgård et al 1993;Vogel 1977Vogel , 1994, we know that Fig. 7 Sponge at site B, with the thermistor probe placed above an osculum.…”

“…The principle of operation is based on the rate of heat removed from a submerged, electrically heated thermistor (temperature sensitive electrical resistor), which is related to the speed of the water mass moving past it (Reiswig 1971(Reiswig , 1974Vogel 1977). The nondirectional flow probe comprised a 0.9-mm diameter glass bead-covered thermistor silicone sealed onto the distal end of a 2-mm diameter stainless steel tube.…”

Hydrodynamic aspects of fish olfaction

“…through viscous entrainment from the posterior nostril. Vogel (1977b) has reported that flow through living sponges, driven by flagella within their interiors, may be assisted by an external current, so there is a precedent for a combined mechanism of this sort in Nature. In at least one case, the lemon shark (Negaprion brevirostris), two mechanisms-the beating of cilia and (probably) an external flow-must act cooperatively to ventilate the organ, each mechanism on its own being insufficient (Zeiske et al 1987(Zeiske et al , p. 2411.…”

Purification, cDNA cloning and expression of a cadmium-inducible cysteine-rich metallothionein-like protein from the marine sponge Suberites domuncula

“…Some marine species filter 24 000 1 kg-' body weight d-' (Vogel 1977) or pump a volume of water equal to their own body volume every 5 s (Reiswig 1974). Hence they 'Corresponding author.…”