Microhabitat influence on young-of-year fish assemblages within the vegetated beds of the St. Louis River estuary

Abstract

Coastal wetlands within the Laurentian Great Lakes provide crucial habitat for an abundance and diversity of fishes during larval and juveniles stages; however, young-of-year fish habitat association studies at the microhabitat scale are rare. Because studies at this fine scale are crucial for understanding the habitat properties that support fishes at this critical life stage, I examined larval and juvenile fish assemblage structure in relation to microhabitat variables within the St. Louis River estuary, a drowned river mouth of Lake Superior. Fish were sampled in aquatic vegetated beds throughout the estuary, across a gradient of aquatic vegetation types and densities. Canonical correspondence analysis, relating species abundances to environmental variables revealed that principally microhabitat variables, including plant species richness, depth, and aquatic plant cover explained difference in fish assemblages. In addition, I evaluated the specific habitat associations of non-native Tubenose Goby (Proterorhinus semilunaris) to provide insight on habitat overlap with native species and further invasion risk. Tubenose Goby were nearly ubiquitous (75% if study sites) and abundant (0.59 fish/m2) in the study site. Non-metric multidimensional scaling revealed that sunfish, Tadpole Madtom and Johnny Darter have the most potential for habitat overlap with Tubenose Goby. Generalized linear modelling revealed that Tubenose Goby occupied a specific microhabitat within vegetated beds consisting of dense cover and high plant species richness. Results from this microhabitat analysis at this critical life stage has potential to inform wetland management and restoration efforts within the St. Louis River estuary and other Great Lake Coastal Wetlands.