Low functional vulnerability of fish assemblages to coral loss in Southwestern Atlantic marginal reefs

Abstract

Marginal reefs sustain coral assemblages under conditions considered suboptimal for most corals, resulting in low coral abundance. These reefs are inhabited by numerous fishes with a generally unknown degree of association with corals that might lead to the assumption that corals play minor roles in determining fish occurrence, when corals could be actually sustaining diverse and resilient assemblages. Using site-occupancy models fitted to data of 113 reef fish species of different life stages (adults and juveniles) from 36 reefs distributed across the Southwestern Atlantic (0.87–27.6°S) we first assessed fish assemblage’s response to coral and turf algal cover, and identified coral-associated fish. Then, we simulated the loss of coral-associated fishes and contrasted it with random losses, providing inferences on the resilience of fish assemblage’s functional trait space to species loss. The entire fish assemblage responded more positively to coral than to turf algae, with 42 (37%) species being identified as coral-associated fish. The simulated loss of coral-associated fish reduced up to 5% the functional trait space and was not different from the random loss. These results reveal that marginal reefs of Southwestern Atlantic reefs host resilient fish assemblages that might preserve fundamental ecological functions and ecosystem services even with coral declines.

Functional diversity patterns of reef fish, corals and algae in the Brazilian biogeographical province

“…Notably, correlation of functional diversity metrics was stronger between corals and fish, and algae and fish, than between corals and algae. This could be explained by the diversity of habitats provided by corals and algae for fish assemblages (Darling et al, 2017; Fulton et al, 2019; Luza et al, 2022), and competition for space between algae and corals (Grillo et al, 2018; Lonzetti et al, 2022). Finally, pairwise residuals' correlations of functional richness and disparity between taxa were overall weak, suggesting that independent mechanisms for each taxonomic group might also be operating in structuring functional diversity along the Brazilian province.…”

“…Such cross‐taxon correlation might emerge from the functional dependence among fish and benthic organisms. Fish frequently rely on habitats provided by corals and algae for foraging, sheltering and reproducing (Darling et al, 2017; Eggertsen et al, 2017; Fulton et al, 2019; Luza et al, 2022). Here, more functionally diverse coral and algal assemblages coincide with fish assemblages with high functional diversity.…”

“…These divergent correlations indicate that more functionally rich fish assemblages are found in reefs with more even coral assemblages, while the converse is not true. It is unclear whether these correlations imply bottom-up or top-down causal effects, that of benthic organisms on fish and, in turn, that of fish on the benthos, given the varied degree of association between these groups in Brazil (Luza et al, 2022). Such patterns are more likely to be driven by a similar response of the assemblages to sea surface temperature, or other variables such as width of the continental shelf (Cord et al, 2022).…”

“…Notably, correlation of functional diversity metrics was stronger between corals and fish, and algae and fish, than between corals and algae. This could be explained by the diversity of habitats provided by corals and algae for fish assemblages (Darling et al, 2017;Fulton et al, 2019;Luza et al, 2022), and…”

Patterns of reef fish taxonomic and functional diversity in the Eastern Tropical Pacific

“…Further, historical predictors that influence surface area and distance from rivers determine species richness and phylogenetic diversity of freshwater fish in the Amazon River (Salgueiro et al 2022). In marine habitats, reef fish species richness varies with coral area (Luza et al 2022), energy availability (Parravicini et al 2013, Barneche et al 2016), and human impacts that concentrate close to reefs (Cinner et al 2018). Although these studies provided important insights regarding the factors determining species richness, disentangling the simultaneous influence of these multiple factors on functional diversity remains a central challenge in community ecology.…”