Linking spatial gradients and habitat to reef fish assemblages: Insights from a remote coral reef system
Drastic loss of Caribbean coral reef habitat in the past decades has recently begun to negatively affect reef fish assemblage structures in the region. Additionally, significant reef fish declines have been caused by local anthropogenic pressures, including even small-scale fisheries. It is commonly suggested that healthy stocks of herbivore fish are needed on reefs to inhibit algal dominance and support coral reef resilience. Despite that the threats and ecological interactions are complex, we can improve our understanding of the impacts on reef fish and their associated benthos by studying their variability along a spatial gradient from land. To that end, data on twelve Underwater Visual Census (UVC) sites of the remote reef system known as the Saba Bank (neighbored by Saba and St. Eustatius) were explored for the relationship between the fish community and the influences of remoteness and benthic cover. As expected, fish density and biomass was generally higher (i.e. at least two-fold increase) at more remote sites and species composition was significantly different between the near- and far sided (i.e. E-NE vs. S-SE, respectively) reefs. In spite of the small-scale operations, the higher fishing pressure in the near-sided reefs mainly suggests that current fish communities at Saba Bank are (partly) shaped by local anthropogenic influences. While this relationship was also expected to be reflected in the trophic community, seemingly contradicting results were found between the univariate and multivariate analyses; top predator proportions were four-fold higher in remote sites, however insignificant trophic composition was found with relation to far-sided reefs. Hence, these particular findings do not allow concluding remarks regarding their potential influences. Besides remoteness, variability in fish assemblages was also significantly linked to gorgonians, bare substrate and macro algae cover. This suggested the driving role of the benthic habitat. Furthermore, a negative relationship between herbivore fish and macro algae was found to suggest the opposing ecological pathway. Nevertheless, the relationship was insignificant and the effectiveness of herbivore fish in controlling algae blooms on the Saba Bank can be strongly debated. Continued data collection of the biotic and abiotic environment from the Saba Bank and other remote reefs, consistent UVC methodology and advancements in multivariate analysis techniques could help reduce our doubts about the local and wide-spread impacts in Caribbean reef systems.
Keywords: coral reefs, reef fish, algae, herbivory, remote, fisheries, Caribbean
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