Habitat dependant growth of three species of bottom settling fish in a coastal fjord

Settlement of juvenile fish is often associated with structurally complex habitat such as eelgrass (Zostera marina L.). We tested whether juvenile Greenland cod (Gadus ogac Richardson), Atlantic cod (G. morhua L.), and white hake (Urophycis tenuis Mitchill) have higher feeding and growth rates in structurally complex eelgrass habitat compared to barren seafloor or the water column. We conducted five single species field experiments from September 2002–October 2003, to test whether juvenile Greenland cod, Atlantic cod, and white hake had higher feeding and growth rates in structurally complex eelgrass habitat compared to barren seafloor or the water column. In two experiments with G. ogac, growth rates did not differ among habitats in autumn 2002, but in autumn 2003 fish grew fastest in the water column (0.449 ± 0.055%·d−1) compared to barren (0.372 ± 0.028%·d− 1) or eelgrass habitats (0.254 ± 0.013%·d− 1). In two experiments with G. morhua, growth rates over the winter (2002–2003) did not differ among habitats, but in spring of 2003 growth was significantly greater in eelgrass (0.366 ± 0.026%·d− 1) compared to barren (0.327 ± 0.035%·d− 1) or water column habitats (0.065 ± 0.013%·d− 1). In one experiment with U. tenuis, growth was faster in eelgrass (0.713 ± 0.062%·d− 1) than barren (0.483 ± 0.055%·d− 1) or water column habitats (0.271 ± 0.040%·d− 1). Zooplankton abundance was consistently highest among seafloor habitats (i.e., eelgrass and barren substrate) and lowest in the water column. More food (by weight) was consumed by U. tenuis and G. ogac in eelgrass than other habitats, while G. morhua consumed the most food over barren substrate. Results are generally consistent with predictions of higher growth rates and food rations among seafloor habitats for white hake and Atlantic cod. Greenland cod did not grow as predicted indicating that potential trade-offs in habitat selection may vary with season and the response to habitat is not uniform among species.

► Growth of juvenile gadiformes varied with habitat type.
► Habitats with increased structural complexity generally promoted faster growth.
► Abundance of zooplankton was lower in water column than seafloor habitats.
► Foraging success was higher along the seafloor than in the water column.
► Foraging success was higher in eelgrass than barren habitats.