The role of apex predators, habitat, and seascape complexity on nearshore fish assemblages in Southeast, Alaska

Abstract

Nearshore marine ecosystems contain dynamic and complex submerged vegetated habitats that offer shelter and prey for juvenile, migratory, and residential species, including many commercial, subsistence, and recreationally important species. The efficacy of the nursery role, shelter, and source of prey of the nearshore is influenced by various abiotic and biotic forces and in this dissertation, we examine the influence of submerged vegetation type, presence of apex predators, and the seascape context on patterns of nearshore fish assemblages in southern Southeast Alaska. We found species-specific responses by juvenile salmon in the nearshore, with seasonality overwhelmingly driving juvenile salmon abundance in eelgrass meadows and Chum Salmon present in greater abundance in understory kelp beds compared to eelgrass meadows, whereas Pink Salmon exhibited no difference. As a known apex predator, the reintroduction of sea otters likewise altered the nearshore fish assemblage with increased richness in eelgrass meadows and assemblage-wide shifts in understory kelps. Finally, in addition to habitat type and apex predators, spatial patterning and presence of adjacent vegetation can affect the nursery role of nearshore habitats. We observed differences in the fish assemblage in eelgrass meadows sampled in homogeneous seascapes with continuous eelgrass meadows and heterogeneous seascapes that included adjacent habitats, including more abundant commercial and forage species in heterogeneous seascapes. This research reinforces the importance of nearshore ecosystems in supporting robust fisheries and highlights the structuring role that submerged vegetation, apex predators, and complex seascapes have in sustaining diverse fish populations. Considering the greater ecological dynamics in the nearshore is vital for decision making in habitat conservation and management and for evaluating its role for fisheries, particularly in the context of increased threats to nearshore ecosystems.