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Do subsurface deposit-feeders partition resources by vertical stratification in the sediment?
A.B. Josefson

It has been proposed that to a great extent deposit-feeding infaunal species partition resources (food and space) by vertical segregation in the sediment, and thereby avoid competitive interactions. Among deposit-feeders, subsurface feeders is a category where interspecific competition may be expected to be a potent structuring force, for the following reasons: l) the food resource (buried organic matter) is predictable; 2) the sediment acts as a refuge decreasing the impact of predation; 3) a high proportion of the species have lecitotrophic larval development which may facilitate co-evolution (co-adaptation). According to some competition theory, interactions are, or have been, most intense between closely related species. In this report the prediction that the following categories of subsurface deposit-feeders segregate vertically in the sediment to a greater extent than other detritivores was tested: All species; Species with high abundance; All confamilials; Confamilials with high abundance; All congenerics; and Congenerics with high abundance. Box-core samples were taken at six different localities, from 30 to 620 m water depth, in the Skagerrak, off the west coast of Sweden. The cores were immediately sectioned on deck, and the animals from each section were determined and enumerated. The niche overlaps (sensu SCHOENER, 1970) in terms of vertical feeding1 dwelling position in the sediment were calculated between all species of detritivores. Comparisons were made between the different species categories and a random sub-set of all detritivorous species. Niche overlaps for any of the species categories were not significantly less than for the random sub-set of species. The average overlap showed the strongest correlation with the degree of concentration of individuals at the sediment surface, and not with for instance water depth (i. e., environmental stability). The results do not corroborate the hypothesis that subsurface deposit-feeders segregate vertically in the sediment as a consequence of competition.

Keywords: deposit-feeders, resources, stratification
Contents of this volume Sci. Mar. 53(2-3) : 307-313 Back PDF
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