Date

Fall 2025

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Geographic differences in ecological communities often arise due to environmental gradients that influence physiological tolerances, species-specific habitat affinities, and various biological interactions. Fish assemblages in temperate upwelling systems, such as the California Current System (CCS), provide an ideal model system to examine these drivers of community structure. Within the CCS, demersal fish communities are often associated with certain benthic habitats, known as fish-habitat associations. To further explore where species are found in relation to certain habitats and location, I used data collected from analysis of stereo-video landers deployed from 2012-2021 to quantify fish-habitat associations across the California coast from Cordell Bank (38.03 N) to San Clemente Island (32.80 N). The data collected included observations of substrate from 1,117 locations and counts of 29,975 fishes, from 115 species. Using the video lander survey information, I evaluated how habitat type (substrate), seafloor complexity, depth, and latitude shaped species richness, density, diversity, community composition, and size structure of fish populations. Hard and mixed-hard substrates consistently supported higher species richness, density, and diversity than soft and mixed-soft habitats. Species richness increased with depth; however, density and diversity decreased with depth. Fish densities were generally higher south of Point Conception (34.45 N), where water temperatures are warmer. Fish community structure was driven foremost by locations along the coast, with significant effects of habitat in certain locations. Ordinations highlighted multiple rockfish (Sebastes) species as key contributors to differences in fish assemblage structure, and indicator-species analysis identified taxa characteristic of specific locations and habitats. Cooler, more temperate rockfishes were found at northern sites and more tropical species were found at southern sites. Habitats with larger rockfishes were observed over higher relief rocky reefs, whereas flatfishes and smaller schooling species were observed over soft sediment, low relief habitats. Fish body size was associated with habitat, relief, and rugosity, such that relatively large individuals within a species were more likely to occur on hard or soft, high relief, high rugosity reefs. Results corroborate previous research to support the need to identify structurally complex hard-bottom habitats as priority areas for monitoring, marine spatial planning, and sustaining productive fisheries. Ecosystem-based spatial planning supported by MPA networks can target biodiversity and fishery management objectives by prioritizing hotspots identified with video surveys, remote sensing, and adaptive monitoring.

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