Date of Award

5-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Wildlife and Fisheries Biology

Committee Chair/Advisor

Brandon Peoples

Committee Member

Luke Bower

Committee Member

Sean Kelly

Abstract

Freshwater fauna on tropical islands face increasing environmental and anthropogenic pressures, yet these systems remain poorly studied. This gap is especially evident in the U.S. Virgin Islands (USVI; St. Croix, St. John, and St. Thomas), where freshwater streams, locally known as “guts,” are scarce, highly variable, and declining. Despite this, no study has comprehensively quantified freshwater fauna across the territory, limiting our understanding of species’ occurrence and ecological patterns. We address these gaps by characterizing species’ rarity across freshwater fishes and decapods and then by evaluating environmental drivers of species occurrence using generalized linear mixed models and assemblage structure using variation partitioning and distance-based redundancy analysis. We sampled 59 sites using backpack electrofishing over two years and recorded a total of 7,336 individuals representing all known native species and several newly documented occurrences in the USVI. Species occurrence was strongly mediated by distance from the ocean and by interactions among connectivity and habitat variables, with some species showing reduced occurrence in systems with more downstream barriers and unfavorable water conditions. Connectivity variables explained more variation in freshwater assemblage structure than local habitat conditions, longitudinal position and dispersal constraints are the primary drivers of freshwater assemblages in USVI guts. Species composition reflected differences in climbing ability and life history. Together, these findings demonstrate that connectivity governs access to habitat in dynamic island systems, while local environmental conditions influence persistence once present. Maintaining longitudinal connectivity, particularly by improving barrier passability, will be critical to conserving freshwater biodiversity in the USVI.

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