Kelp Forest Zooplankton, Forage Fishes, and Juvenile Salmonids of the Northeast Pacific Nearshore

Abstract

AbstractKelp forests are an important ecological component of temperate coastal systems that are sensitive to anthropogenic disturbance and are in decline in many locations globally. In the northeastern Pacific Ocean off the coast of Washington, USA, bull kelp Nereocystis luetkeana forests are seasonally used by juvenile salmonids and forage fishes; however, details on ecosystem functional linkages for forage fishes and salmonids are not well quantified. Using a zooplankton drop net and snorkel surveys for fishes, we sampled two bull kelp forests across multiple years. Our goal was to quantify differences in the communities of zooplankton, juvenile salmonids (Chinook Salmon Oncorhynchus tshawytscha and Coho Salmon O. kisutch), and forage fishes (Pacific Herring Clupea pallasii, Surf Smelt Hypomesus pretiosus, and Pacific Sand Lance Ammodytes hexapterus) between kelp forests and adjacent nonkelp (open‐water) habitats. We tested the hypothesis that zooplankton common in the diets of surface‐oriented forage fishes and juvenile salmonids would be more abundant in kelp than in open water. At the overall assemblage level of organization, kelp and open‐water habitats had similarly abundant and diverse zooplankton communities. However, decapods and phytal‐associated harpacticoid copepods within this assemblage (i.e., groups that are an important component of fish diets) were significantly more abundant in kelp forests than in open‐water habitat. Greater presence and abundance of zooplankton, juvenile salmonids, and forage fishes in kelp forests compared to adjacent open‐water habitats suggest that kelp forests are important for culturally and economically valuable forage fishes and salmonids and warrant further study to define and conserve their ecosystem function.