Effect of nursery habitat on density-dependent habitat selection in juvenile flatfish

Abstract

Nursery habitats contribute significantly to adult recruitment of marine fish, but the density of juveniles that they can support depends in part on conspecific interactions among juveniles. Density-dependent habitat selection (DDHS) was compared in the laboratory using two species of age-0 yr flatfish: 1) English sole Pleuronectes vetulus, which utilizes estuarine nurseries at high densities and 2) northern rock sole Lepidopsetta polyxystra, which occurs at lower densities in coastal nurseries and is known to exhibit DDHS. The pattern of DDHS was hypothesized to be similar in both species, but to initiate at higher densities and be less responsive to predation risk in English sole. Trials were conducted over eight density treatments (0.4, 0.8, 1.5, 3.0, 6.1, 12.2, 18.6, and 23.8 fish m − 2 ), both with and without predation risk, and offered fish equal access to a preferred sand habitat and a less-preferred gravel habitat. Rock sole showed typical DDHS by increasing percentage use of the gravel habitat as conspecific density increased, with DDHS initiated at about 1.5 fish m − 2 . English sole showed no DDHS: there was no relationship between percentage use of gravel habitat and conspecific density. Predation risk caused rock sole to significantly decrease gravel usage across all densities, but did not significantly change habitat selection for English sole. These results suggest that each species may be behaviorally adapted to the conspecific density and predation risk of their respective nursery habitats, and correspond well with the comparatively risk-prone behaviors of English sole. The relationship between nursery habitat and density-dependent behavior may be further understood by studies integrating factors such as turbidity, food resources and ontogeny.