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Spatial gradients in predation pressure and their influence on the dynamics of two littoral bivalve populations
Griffiths, C.L. (1990). Spatial gradients in predation pressure and their influence on the dynamics of two littoral bivalve populations, in: Morton, B. (Ed.) The Bivalvia: Proceedings of a Memorial Symposium in honour of Sir Charles Maurice Yonge (1899-1986) at the 9th International Malacological Congress, 1986, Edinburgh, Scotland, UK. pp. 321-332
In: Morton, B. (Ed.) (1990). The Bivalvia: Proceedings of a Memorial Symposium in honour of Sir Charles Maurice Yonge (1899-1986) at the 9th International Malacological Congress, 1986, Edinburgh, Scotland, UK. Hong Kong University Press: Hong Kong. ISBN 962-209-273-X. 355 pp., more

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    Marine

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  • Griffiths, C.L.

Abstract
    The interactive roles of predation, competition and tidal elevation in structuring populations of two contrasting bivalve species, the cockle Cerastoderma edule and the mussel Choromytilus meridionalis, were compared. Cockles settled at relatively low densities throughout the adult range and thereafter grew at a rate that declined with tidal elevation. Competition for space was not thought to result in significant mortality, but shore crabs (Carcinus maenas) fed voraciously on small cockles low on the shore and oystercatchers on large ones high on the shore. As a result lowshore populations consisted only of new settled spat and the few large individuals that had survived to accumulate in the largest size classes. Higher up the shore cockles survived well until they became attractive to oystercatchers, after which they were rapidly eliminated. Mussels settled at high densities and grew rapidly, competing intensely with one another for space as they did so. They were attacked by a wide range of predators, each differing in distribution pattern, feeding rate and in the size range of prey preferred. Despite the density and diversity of the predator array, however, predatory losses fell well below those attributable to self thinning, particularly where mussel growth rates were at their fastest early in life and low on the shore.

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