Dissertation Defense

This dissertation examined the ecological forces shaping cryptobenthic reef fish communities across three Western Atlantic ecoregions: the Gulf of Mexico, western Caribbean, and southwestern Caribbean. Cryptobenthic reef fishes are small, diverse, and ecologically important benthic-associated fishes that include many habitat specialists. Their small size, diversity, and tight association with the seafloor make them a useful model for community ecology, yet many regions remain poorly documented. My aims were to i) characterize the cryptobenthic fish community and its habitat associations in an understudied region (the southwestern Gulf of Mexico), ii) assess the ecological forces that shape community assembly across the Greater Caribbean, and iii) identify behavioral patterns that underpin microhabitat associations in a specialist and generalist species of cryptobenthic fishes in an anthropogenically disturbed system.

I address these aims in three research chapters. Chapter 2 provides the first quantitative assessment of cryptobenthic reef fishes in the Veracruz Reef System in the southwestern Gulf of Mexico. Using standardized clove-oil collections across reef outcrops and specific microhabitats, I found that community composition was strongly shaped by selection associated with microhabitat type and availability. Chapter 3 assesses how ecological forces interact across the three ecoregions. I sampled fish communities, documented species-specific microhabitat associations as functional traits, examined patterns in taxonomic and functional diversity across regions, and generated species-microhabitat interaction networks. The western Caribbean supported the highest diversity, providing evidence for strong selection-based dynamics for local community assembly. In the southwestern Caribbean, resolved patterns suggest that human disturbance is shifting community assembly toward stochastic processes and greater homogeneity. In the Gulf of Mexico, low taxonomic and functional diversity and less modular species-microhabitat networks likely reflect isolation from the regional species pool, environmental filtering, and drift. Finally, Chapter 4 compares habitat preferences of a generalist and specialist goby species in controlled aquarium trials, simulating sedimentation as an anthropogenic disturbance, and examines patterns of community structure in a disturbed system relative to sediment depth. The specialist Elacatinus illecebrosus relied on coral replicas, showed strong site fidelity, and exhibited no response to sedimentation, with substantial individual variability. By contrast, the generalist Coryphopterus glaucofraenum showed higher swimming activity and limited use of coral replicas, and high homogeneity across the tested population. I found no correlation between cryptobenthic fish community structure and composition and ambient sediment loads in the field. 

Collectively, my findings suggest that cryptobenthic reef fish assemblages in the Neotropics are structured by the interplay of regional and local processes, with strong roles for local microhabitat availability and species-specific habitat use patterns. High diversity emerges where the regional species pool is rich and local benthic composition is heterogeneous, which sets the stage for a strong role of ecological selection in governing community assembly. In contrast, spatial isolation and human disturbance reduce diversity and boost the role of stochastic processes. Stable conditions foster diversity through niche differentiation, while variability, constraints, and isolation increase stochasticity and reduce diversity. My work shows that cryptobenthic reef fishes are sensitive to changes in benthic composition, with specialists particularly vulnerable to habitat loss. Conserving habitat heterogeneity and connectivity among reefs may therefore be essential to maintaining the processes that generate and sustain cryptobenthic fish communities in the Western Atlantic.