Date

Fall 2025

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Fish species are not randomly distributed across space and changes in fish assemblages often occur in response to environmental variation, habitat characteristics, and species interactions, which are often scale-dependent. Understanding fine scale habitat associations can contribute to marine spatial planning, modeling efforts, and marine resource management. While habitat associations have been observed and studied on a variety of different scales, there is a distinct lack of information about how these factors influence fish assemblages in mesophotic depths in temperate ecosystems. In this study, I investigated species-habitat associations of demersal fish communities within an intermediate depth zone (20 60 m) and identified the importance of different habitat variables in shaping these communities. Using remote underwater video platforms equipped with stereo-video, I examined how abundance, size, diversity, species richness, and community composition changed at three different sites, with respect to three different habitat and environmental variables: depth, habitat complexity, and wave energy/exposure. Overall, fish communities did not differ significantly across the depth range examined, although fish abundance was positively associated with depth at one site, suggesting its importance is likely site specific. Certain habitat characteristics, such as relief and rugosity, singularly contributed to changes in diversity and species richness. Others, such as vector ruggedness measure and topographic position index worked in combination with depth, to explain observed differences in fish abundance and fish body size, with both abundance and size increasing along a depth gradient in areas of high habitat complexity. Wave energy negatively influenced fish abundance at the more exposed site, and wave exposure may also have driven overall differences in body size. This work highlights how environmental and habitat characteristics influence fish communities differently at different locations, despite similar species and close proximity. Future research should aim to include more environmental variables to further our knowledge regarding specific habitat associations. This knowledge can be used to inform future species distribution modeling efforts, along with future marine spatial planning. With the growing use and implementation of marine spatial protections, accurate species-habitat models are important to help reduce survey efforts and cost, and ensure spatial protections are appropriately designated.

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