Functional Mechanisms of Control in the Bivalve Pump: an Experimental Approach to Resolve Current Controversy

University Of Connecticut, Storrs CT

Investigators

Abstract

Functional Mechanisms of Control in the Bivalve Pump: An Experimental Approach to Resolve Current Controversy J. Evan Ward and Sandra Shumway University of Connecticut Bivalve molluscs (e.g., clams, oysters, scallops) are found in almost all depths in marine, estuarine and freshwater environments. These organisms obtain their food by filtering particles from the water surrounding them. They possess highly efficient and complicated mechanisms for extracting these particles, and therefore are significant ecologically in coupling water-column and bottom communities. They exert great control over the supply and distribution of particles (their food) in many coastal ecosystems, and thus can influence the general well-being of other organisms as well as the overall environment. Because these organisms play such a key role in ecosystems, it is important to understand how they obtain and process food and non-food particles, and the intrinsic and extrinsic controls of the feeding process. The ability to study feeding processes of bivalves has been linked with advances and application of analytical equipment. These investigators have pioneered the use of two systems, flow cytometry and video endoscopy, in studies related to suspension feeders. In doing so, they have greatly increased our understanding of the functional morphology of feeding structures and kinematics of particle capture, transport, rejection, and ingestion in several groups of suspension feeders. In the present study, two new techniques will be used, a newly developed Pressure-Gape System and Particle Image Velocimetry (PIV). These methods will further our understanding of the physiological bases of water processing, i.e. pumping and filtration, in bivalve molluscs. The research is divided into three major projects and will examine feeding in three species of bivalves, each with a specific gill structure: blue mussels (Mytilus edulis), eastern oysters (Crassostrea virginica) and sea scallops (Placopecten magellanicus). The overall objectives are to: 1) Investigate the functional mechanisms of water processing in suspension feeding bivalves at levels of both the organism and organ using newly developed techniques, and 2) Test key assumptions of existing models of water-pumping performance in bivalves. Experiments are designed to: a) Determine relationships between pumping pressure and rate (volume flux) to obtain base-line data on pumping characteristics for the three bivalve species; b) Investigate mechanisms by which bivalves alter pumping activity by examining potential loci for control, e.g. changes in lateral cilia activity, valve gape, contractions of the gill; c) Test the hypotheses that bivalve pumping activity is a binary process (on/off), or an autonomous process; d) Test the hypothesis that bivalve pumping activity is mediated by exogenous factors, such as food quantity and quality, and is under compensatory control; e) Examine the variation in pumping behavior and performance among the three bivalve species. This research has the potential to resolve some of the long-standing controversies regarding the physiological basis of water processing in bivalves, and to provide a starting point for the study of these processes in other suspension-feeding invertebrates. The approach is unique in that the researchers are integrating several techniques to study mechanisms associated with a fundamental process, filter feeding, at both the organ and organism level. The researchers will be able to relate these findings to performance by the animals in the natural environment. Graduate and undergraduate students will be involved in all aspects of the study and participation by females and underrepresented minorities will be encouraged.