Area-dependent patterns of finfish diversity in a large marine ecosystem

The species-area relationship (SAR) is considered a cornerstone of terrestr ial and freshwater ecology and conservation. It has rarely been examined in a large marine ecosystem because it has been assumed that sufficient data are lacking and (or) the scales of oceanic systems are too large. Using dat a drawn from fishery surveys, we show a positive relationship between the n umber of finfish species and the area of submarine, offshore banks on the c ontinental shelf off eastern Canada. Banks of similar size yielded similar species richness regardless of the distance between them. Area per se had a stronger influence on species number than did habitat diversity. The slope of SAR observed is consistent with the tendency for many of the species to be highly migratory with widely dispersing offspring. This results in stro ng interactions among banks. The combined densities of all species increase d with bank area, suggesting that larger banks have higher resources per un it area. Populations and species on larger banks should be more resilient t o local extinctions relative to those on smaller banks, and natural or huma n-induced perturbations might be expected to impact the community structure of the small, extinction-prone populations at a faster rate.