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Reef-dwelling Fish Resilience Despite Widespread Coral Bleaching

Paper Reviewed
Wismer, S., Tebbett, S.B., Streit, R.P. and Bellwood, D.R. 2019. Spatial mismatch in fish and coral loss following 2016 mass coral bleaching. Science of the Total Environment 650: 1487-1498.

In setting the stage for their work, Wismer et al. (2019) state that it is generally assumed that a loss of live coral due to a coral bleaching event results "in a proportional net loss of coral-dependent reef fishes." Yet they write that "no studies, to the best of our knowledge, have explicitly tracked host corals through a mass bleaching event and quantified the changes in the associated reef fish assemblage." Thus, they add, "the direct impact of individual coral bleaching, and subsequent mortality, on its 'resident' or closely associated reef fish assemblages is still largely unknown."

In an attempt to fill this data void, the team of four Australian researchers employed a new methodology to "explicitly test the assumption that coral mortality leads to the loss of resident fishes." The methodology included the use of generalized linear mixed effects models to examine differences in the proportional cover of corals, fish abundance and fish species richness that were observed before, during and after a major coral bleaching event at Lizard Island, an island situated in the northern region of the Great Barrier Reef, Queensland, Australia. Date utilized in the study were collected at Lizard Island (1) in January and February of 2016 just prior to a bleaching event, (2) in April 2016 during the peak of bleaching, and (3) in October of 2016, six months post-bleaching.

So what did their analysis reveal?

Wismer et al. report observing an overall decrease in both the cover of live coral and number of resident reef fishes in response to the mass bleaching event. However, they note that "patterns at a local, 1 m2 scale, were invariably spatially mismatched" such that "reef fishes were able to persist at degraded sites that were devoid of live coral and or inundated with cyanobacteria, while other sites exhibited considerable increases in post-bleaching fish abundance." What is more, they found that "the effects of coral loss on obligate live coral-dwelling [fish] species were surprisingly limited, compared to the staggering loses of live Acropora."

In commenting on their findings, the authors say that "these results challenge commonly held assumptions regarding the tight link between live coral-dwelling damselfishes and habitat-forming Acropora corals," adding that "the relationship between fish loss and coral loss, therefore, appears to be a rather complex one, and care is needed when ascribing causality from observed patterns obtained from larger spatial scales." Consequently, Wismer et al. conclude that their results (1) "offer a degree of optimism, albeit cautious, that fishes are far more behaviorally resilient than we may have previously assumed based on correlations at larger spatial scales," and that they (2) "highlight the potential for short-term resilience to climate change, in fishes, through local migration and habitat plasticity."

Posted 11 January 2019