Nature of relation between ventilation and oxygen consumption in filter feeders

Abstract

Correlations between rates of ventilation and oxygen consumption in filter feeders are usually interpreted in terms of causal relations, but authors disagree on whether ventilation is regulated to meet respiratory needs or whether oxygen consumption reflects energetic costs of water transport. It seems, however, that neither causality applies, the correlations being determined by physical characteristics of the ventilatory systems. The ventilatory currents both in a tube dwelling worm, Urechis caupo, and in bivalves, such as Mytilus edulis, are laminar, and oxygen in the water is available to the animals solely by diffusion. Various estimates of the diffusive boundary layer 6, developing at the interface between the ventilatory current and the body surface of U. caupo and mantle cavity in M. edulis, were in good agreement. The estimates of 6 amounted to about 0.1 mm, or a small fraction of the thickness of the ventilatory current, indicating that the larger part of the dissolved oxygen in the current is unavailable to the animals. At low rates of ventilation oxygen uptake is governed by the condition of diffusion in the ambient water. Oxygen consumption increases steeply with increasing ventilation until threshold levels are reached, and processes within the body become limiting for the rate of oxygen consumption. Oxygen consumption approaches independency of ventilation at ventilatory rates amounting to only one-fifth or less of the rates of the undisturbedly filtering animal. Regulation of respiration by means of ventilatory regulation thus seems incompatible with filter feeding in habitats that require high rates of water processing. The energetic costs of ventilation are insignificant. Presumably, in most habitats, water processing at low costs is a prerequisite for a life based on filter feeding.

Seasonality of in situ respiration rate in three temperate benthic suspension feeders

“…Physical factors-including temperature, salinity, ambient oxygen concentration, and water flow-and trophic effectsincluding particle size, filtration activity, and food concentration-have all been suggested as important factors that affect respiration of benthic filter feeders (Jørgensen et al 1986;Sebens 1987;Patterson et al 1991;Lucas 1996;Riisgård and Larsen 2001). Any measured respiration rate is composed of several processes that may include the costs of (1) basal metabolism, (2) locomotion activity, and (3) secondary production (i.e., synthesis of somatic and reproductive tissue).…”

“…In their natural environments, organisms are subjected to the combined effect of several factors. Temperature, salinity, ambient oxygen concentration, water flow, size, investment in secondary production, state of expansion and contraction, filtration activity, and food concentration have been suggested as important factors that affect respiration (e.g., Jørgensen et al 1986;Sebens 1987;Patterson et al 1991;Lucas 1996;Riisgård and Larsen 2001). By obtaining measurements in the natural environment as well as repeating them throughout the year, we examined respiration rate within the natural range of conditions to which organisms are subjected.…”

Particle capture mechanisms in suspension-feeding invertebrates

“…Echiurans: Urechis caupo is a large mucus-net filterfeeding echiuran worm living in a U-shaped burrow in mudflats along the Pacific coast of California. The filter-feeding behavior of U. caupo has been thoroughly studied under laboratory conditions (Fisher & MacGinitie 1928, Hall 1931, MacGinitie 1945, Jørgensen 1955, Lawry 1966, Pritchard & White 1980, Jørgensen et al 1986, Julian et al 2001) and in the field (Osovitz & Julian 2002). It pumps seawater using anterior-toposterior peristaltic muscular contractions of its body wall, and the water current is filtered through a funnelshaped mucus net that is secreted by specialized glands near the worm's proboscis and which surrounds the anterior end of the body.…”

Magnetic resonance imaging analysis of water flow in the mantle cavity of live Mytilus galloprovincialis

“…However, there is a lack of knowledge regarding volume flow in the mantle cavity. For example, the patterns of flow through the mantle cavity of the mussel are presumably less well defined, and it is necessary to assume a cross-sectional area and length for the mantle cavity to analyse the water flow (Jørgensen et al, 1986a). Indeed, even using a dissecting microscope, water flow is normally estimated by the movement of particles.…”

“…The suspended particles are then filtered by the gill, and the water leaves from the exhalant siphon (Wallengren, 1905;Mill, 1972;Jørgensen et al, 1986a). Intensive studies have been conducted to measure the filtration rate, using either particle clearance or direct measurements of inhalant and exhalant flows (Bayne, 1976;Kiøboe et al, 1980;Riisgård, 2001).…”