112 P
. Sobral, J. Widdows J. Exp. Mar. Biol. Ecol. 245 2000 111 –125
natural environment containing a mixture of phytoplankton, suspended benthic algal cells and silt.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Current velocity; Feeding activity; Particle selection; R. decussatus; Scope for growth; Turbidity
1. Introduction
Water currents are essential for the supply of suspended food particles, including phytoplankton, microphytobenthic organisms and resuspended sediment particles to
sessile suspension-feeding bivalves. Current velocity influence sediment dynamics, as well as settlement of the larval stage, and the feeding and growth of adult benthic
animals Kirby-Smith, 1972; Walne, 1972; Wildish and Peer, 1983; Wildish and Kristmanson, 1997.
Furthermore, hydrodynamics are important in determining the settlement of bivalve ´
larvae Andre et al., 1993 and thus recruitment of species to the benthos. However, relatively few studies have examined the performance of marine organisms in response
to a wide range of current velocities. Wildish et al. 1987, 1992, Wildish and Kristmanson 1985 and Wildish and Miyares 1990 have examined the feeding
responses to flow-rate in Mytilus edulis and Placopecten magellanicus. The influence of flow velocity on growth was studied on Argopecten radians by Cahalan et al. 1989, on
Mercenaria mercenaria and Crassostrea virginica by Grizzle et al. 1992 and on Modiolus modiolus by Lesser et al. 1994.
˜ In the Ria Formosa lagoon system, freshwater input is minimal Falcao and Vale,
1990, and the tidal water movement is the principal process generating currents. Tidal processes together with storm generated waves and currents have a major role in the
evolution of the barrier islands of the Ria Formosa system Pilkey et al., 1989. The lagoon is largely filled with an accumulation of fine sediment in salt marshes and
the tidal-delta sands. This fine sediment is readily resuspended by tidal currents and storm conditions and therefore turbidity and the concentration of suspended particulate
matter in estuarine and coastal systems show tidal, seasonal and inter-annual variation. R
. decussatus an infaunal bivalve of tidal flats in the Ria Formosa, is consequently exposed to wide variations in both water currents and suspended particulate matter
SPM. In this dynamic system resuspension of sediment is a common feature and the ability of clams to filter and select the appropriate food particles will determine their
performance and growth. Several studies indicate that suspended bottom material is an important food source for suspension feeding bivalves such as M
. edulis Kiørboe et al., 1980, 1981; Bayne et al., 1987, Spisula subtruncata Møhlenberg and Kiørboe, 1981
and Ostrea edulis Grant et al., 1990. There are no previous studies on the feeding responses of R
. decussatus to changing current velocities and SPM, two variables that co-vary in the estuarine and coastal
environment. Therefore the objective of this study was to investigate the effects of current velocity and suspended particulate matter SPM on the feeding rate and particle
selection efficiency of the clam R . decussatus.
P . Sobral, J. Widdows J. Exp. Mar. Biol. Ecol. 245 2000 111 –125
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2. Materials and methods
