Distribution of diversity and functional groups of marine benthic infauna in the Skagerrak (eastern North Sea) - Can larval availability affect diversity?

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Abstract
In the eastern Skagerrak a major discontinuity in distribution of species and larval developmental modes of soft-sediment infauna coincides with the border between two distinct current systems. The shelf area, overflown by coastal currents (composed of North Sea and Baltic water) harbours a diverse fauna of interface-feeding species, and planktotrophic larval development is equally common as lecithotrophic development. The basin area, overflown by a current of Atlantic continental-slope origin, which shows up-welling in the basin, harbours a fauna where the interface-feeding category has low diversity and where the planktotrophic mode of development is uncommon. While subsurface detritivores were positively correlated with the amount of sedimenting degradable organic matter, interface feeders showed no clear correlation, and abundance of this category was less variable spatially than the abundance of subsurface feeders. This suggests that numbers of subsurface detritivores are food-limited in the areas with low sedimentation. Several hypotheses to explain the differences in diversity between the two areas are discussed, and it is concluded that the ‘stability-time hypothesis’ does not provide an acceptable explanation. The observed diversity pattern is in accordance with five different hypotheses namely: ‘habitat complexity’, ‘intermediate disturbance’, ‘larval pool’, ‘island biogeography’ and ‘resource diversity’. It is suggested that the major determinants of species diversity within the studied area, are limits set by the physical environment. Factors affecting larval dispersal may be important.

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