Spatial mismatch in fish and coral loss following 2016 mass coral bleaching.

Record-breaking temperatures between 2015 and 2016 led to unprecedented pan-tropical bleaching of scleractinian corals. On the Great Barrier Reef (GBR), the effects were most pronounced in the remote, northern region, where over 90% of reefs exhibited bleaching. Mass bleaching that results in widespread coral mortality represents a major disturbance event for reef organisms, including reef fishes. Using 133 replicate 1 m2 quadrats, we quantified short-term changes in coral communities and spatially associated reef fish assemblages, at Lizard Island, Australia, in response to the 2016 mass bleaching event. Quadrats were spatially matched, permitting repeated sampling of fish and corals in the same areas: before, during and 6 months after mass bleaching. As expected, we documented a significant decrease in live coral cover. Subsequent decreases in fish abundance were primarily driven by coral-associated damselfishes. However, these losses, were relatively minor (37% decrease), especially compared to the magnitude of Acropora loss (>95% relative decrease). Furthermore, at a local, 1 m2 scale, we documented a strong spatial mismatch between fish and coral loss. Post-bleaching fish losses were not highest in quadrats that experienced the greatest loss of live coral. Nor were fish losses associated with a proliferation of cyanobacteria. Several sites did, however, exhibit increases in fish abundance suggesting substantial spatial movements. These results challenge common assumptions and emphasize the need for caution when ascribing causality to observed patterns of fish loss at larger spatial scales. Our results highlight the potential for short-term resilience to climate change, in fishes, through local migration and habitat plasticity.

Wismer S ，Tebbett SB ，Streit RP ，Bellwood DR ... -  《-》

Ecosystem restructuring along the Great Barrier Reef following mass coral bleaching.

Stuart-Smith RD ，Brown CJ ，Ceccarelli DM ，Edgar GJ ... -  《-》

Predicting climate-driven regime shifts versus rebound potential in coral reefs.

Graham NA ，Jennings S ，MacNeil MA ，Mouillot D ，Wilson SK ... -  《-》

Mass coral bleaching causes biotic homogenization of reef fish assemblages.

Global climate change is altering community composition across many ecosystems due to nonrandom species turnover, typically characterized by the loss of specialist species and increasing similarity of biological communities across spatial scales. As anthropogenic disturbances continue to alter species composition globally, there is a growing need to identify how species responses influence the establishment of distinct assemblages, such that management actions may be appropriately assigned. Here, we use trait-based analyses to compare temporal changes in five complementary indices of reef fish assemblage structure among six taxonomically distinct coral reef habitats exposed to a system-wide thermal stress event. Our results revealed increased taxonomic and functional similarity of previously distinct reef fish assemblages following mass coral bleaching, with changes characterized by subtle, but significant, shifts toward predominance of small-bodied, algal-farming habitat generalists. Furthermore, while the taxonomic or functional richness of fish assemblages did not change across all habitats, an increase in functional originality indicated an overall loss of functional redundancy. We also found that prebleaching coral composition better predicted changes in fish assemblage structure than the magnitude of coral loss. These results emphasize how measures of alpha diversity can mask important changes in the structure and functioning of ecosystems as assemblages reorganize. Our findings also highlight the role of coral species composition in structuring communities and influencing the diversity of responses of reef fishes to disturbance. As new coral species configurations emerge, their desirability will hinge upon the composition of associated species and their capacity to maintain key ecological processes in spite of ongoing disturbances.

Richardson LE ，Graham NAJ ，Pratchett MS ，Eurich JG ，Hoey AS ... -  《-》

Climate-driven shift in coral morphological structure predicts decline of juvenile reef fishes.

Rapid intensification of environmental disturbances has sparked widespread decline and compositional shifts in foundation species in ecosystems worldwide. Now, an emergent challenge is to understand the consequences of shifts and losses in such habitat-forming species for associated communities and ecosystem processes. Recently, consecutive coral bleaching events shifted the morphological makeup of habitat-forming coral assemblages on the Great Barrier Reef (GBR). Considering the disparity of coral morphological growth forms in shelter provision for reef fishes, we investigated how shifts in the morphological structure of coral assemblages affect the abundance of juvenile and adult reef fishes. We used a temporal dataset from shallow reefs in the northern GBR to estimate coral convexity (a fine-scale quantitative morphological trait) and two widely used coral habitat descriptors (coral cover and reef rugosity) for disentangling the effects of coral morphology on reef fish assemblages. Changes in coral convexity, rather than live coral cover or reef rugosity, disproportionately affected juvenile reef fishes when compared to adults, and explained more than 20% of juvenile decline. The magnitude of this effect varied by fish body size with juveniles of small-bodied species showing higher vulnerability to changes in coral morphology. Our findings suggest that continued large-scale shifts in the relative abundance of morphological groups within coral assemblages are likely to affect population replenishment and dynamics of future reef fish communities. The different responses of juvenile and adult fishes according to habitat descriptors indicate that focusing on coarse-scale metrics alone may mask fine-scale ecological responses that are key to understand ecosystem functioning and resilience. Nonetheless, quantifying coral morphological traits may contribute to forecasting the structure of reef fish communities on novel reef ecosystems shaped by climate change.

Fontoura L ，Zawada KJA ，D'agata S ，Álvarez-Noriega M ，Baird AH ，Boutros N ，Dornelas M ，Luiz OJ ，Madin JS ，Maina JM ，Pizarro O ，Torres-Pulliza D ，Woods RM ，Madin EMP ... -  《-》