Kelp beds as fish and invertebrate habitat in southeastern Alaska

Abstract

Throughout the temperate marine regime, the shallow subtidal is dominated by rocky reefs and algal assemblages. The ecological significance of high-latitude, cold-water kelp systems is poorly understood particularly for Alaska. Two large-scale experiments conducted near Juneau, Alaska were designed to study fish and invertebrate assemblages in regard to (1) canopy forming Nereocystis luetkeana (1500 m² manipulations) and (2) sub-canopy forming Laminaria bongardiana (600 m²). Fish and invertebrates were quantified using Standard Monitoring Units for the Recruitment of Fish (SMURFs), light traps, and visual surveys. The canopy kelp experiment revealed significantly greater abundance (X=0.57 fish/SMURF; X=0.28 fish/SMURF) and biomass (X=0.95 g/SMURF; X =0.23 g/SMURF) of benthic fishes at Nereocystis sites versus sites without canopy kelp. In contrast, a direct negative effect of Nereocystis was observed for schooling fish; significantly more fish were observed at sites without canopy kelp as compared to Nereocystis sites (X=27.3 fish/15 m³; X=4.2 fish/15 m³). Fish assemblages were independent of L. bongardiana, yet invertebrates were twice as abundant at sub-canopy sites. Nereocystis has direct and indirect effects on fish distributions through behavioral and habitat modifications. Overall, canopy kelps with associated sub-canopy kelps promote more abundant and rich fish assemblages in southeastern Alaska, while invertebrate assemblages are greater in sub-canopy areas.