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Author ORCID Identifier

https://orcid.org/0000-0002-5623-9323

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Marine Sciences and Technology

Year Degree Awarded

2019

Month Degree Awarded

May

First Advisor

Andy Danylchuk

Second Advisor

Adrian Jordaan

Third Advisor

Gregory Skomal

Subject Categories

Marine Biology

Abstract

The structural complexity of aquatic habitats can influence the ecological processes that occur within them, as fine-scale topographic features act as refugia for small fishes, buffering the effects of environmental stressors. Accordingly, the habitat requirements of juvenile demersal fishes in shallow littoral zones are often defined by their associations with distinct benthic microhabitats, such as densely vegetated substrates. However, an array of ecologically-important juvenile fishes also associate with topographically-homogeneous, sparsely-vegetated substrata. Absent the benefits offered by structural refugia, such fishes may be more affected by environmental variability and may have evolved distinct strategies for coping with stressors. I examined this hypothesis by assessing the factors shaping juvenile fish assemblages across the littoral zones of a subtropical island, where I predicted that flow-related stress and positive social interactions would be influential in governing the distributions of species occupying open, unstructured habitats. Spatio-temporal variability in the strength of wave-and tide-driven water movement were among the principal drivers of habitat use for a variety of juvenile fishes, exerting the most pronounced effects on species with an aversion to dense benthic vegetation (i.e., Bothus spp., and Albula vulpes), with little impact on species inhabiting seagrass (Haemulon spp. and Halichoeres bivittatus). Spatial segregation between A. vulpes and its cryptic congener Albula goreensis was unrelated to benthic habitat characteristics but well-explained by differential relationships with wave exposure, suggesting that niche partitioning between these functionally-indistinct species was mediated by flow. After accounting for phenotypic clustering caused by an extensive suite of environmental filters, residual correlations in species abundance were dominated by strongly- asymmetric positive associations, primarily between soft-bottom benthivores and Eucinostomus spp. Interspecific relationships were weak among seagrass-associated taxa. Disparities in the foraging behaviors and putative vigilance-keeping abilities of Eucinostomus spp. and its associate A. vulpes implied that the large organizational influence of eucinostomids could be explained by their capacity for producing risk-related information, which more vulnerable species exploited. Collectively, these findings support the hypothesis that fishes using unstructured habitats are more exposed to flow-related stress than those occupying complex habitats, and likewise that they employ alternative antipredator strategies, relying on social mechanisms to reduce predation risk.

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