Ecosystem restructuring along the Great Barrier Reef following mass coral bleaching

Abstract

Global warming is markedly changing diverse coral reef ecosystems through an increasing frequency and magnitude of mass bleaching events. How local impacts scale up across affected regions depends on numerous factors, including patchiness in coral mortality, metabolic effects of extreme temperatures on populations of reef-dwelling species and interactions between taxa. Here we use data from before and after the 2016 mass bleaching event to evaluate ecological changes in corals, algae, fishes and mobile invertebrates at 186 sites along the full latitudinal span of the Great Barrier Reef and western Coral Sea. One year after the bleaching event, reductions in live coral cover of up to 51% were observed on surveyed reefs that experienced extreme temperatures; however, regional patterns of coral mortality were patchy. Consistent declines in coral-feeding fishes were evident at the most heavily affected reefs, whereas few other short-term responses of reef fishes and invertebrates could be attributed directly to changes in coral cover. Nevertheless, substantial region-wide ecological changes occurred that were mostly independent of coral loss, and instead appeared to be linked directly to sea temperatures. Community-wide trophic restructuring was evident, with weakening of strong pre-existing latitudinal gradients in the diversity of fishes, invertebrates and their functional groups. In particular, fishes that scrape algae from reef surfaces, which are considered to be important for recovery after bleaching, declined on northern reefs, whereas other herbivorous groups increased on southern reefs. The full impact of the 2016 bleaching event may not be realized until dead corals erode during the next decade. However, our short-term observations suggest that the recovery processes, and the ultimate scale of impact, are affected by functional changes in communities, which in turn depend on the thermal affinities of local reef-associated fauna. Such changes will vary geographically, and may be particularly acute at locations where many fishes and invertebrates are close to their thermal distribution limits.

Seabird nutrient subsidies alter patterns of algal abundance and fish biomass on coral reefs following a bleaching event

“…The lack of response to bleaching by herbivores and piscivores is consistent with previous studies, which demonstrate that immediately following bleaching events, these groups are either unaffected or exhibit short-term increases in abundance due to an increase in food availability (Pratchett et other hand, corallivores and planktivores often experience sharp declines within three years of mass bleaching events Pratchett, Wilson, & Baird, 2006;Stuart-Smith, Brown, Ceccarelli, & Edgar, 2018;Wilson et al, 2006). The lack of response to bleaching by herbivores and piscivores is consistent with previous studies, which demonstrate that immediately following bleaching events, these groups are either unaffected or exhibit short-term increases in abundance due to an increase in food availability (Pratchett et other hand, corallivores and planktivores often experience sharp declines within three years of mass bleaching events Pratchett, Wilson, & Baird, 2006;Stuart-Smith, Brown, Ceccarelli, & Edgar, 2018;Wilson et al, 2006).…”

Refugia under threat: Mass bleaching of coral assemblages in high‐latitude eastern Australia

“…Against the backdrop of species migrations (Baird, Sommer, & Madin, ) and tropicalisation of high‐latitude marine ecosystems (Smale et al, ; Vergés et al, , ; Wernberg et al, ), taxon‐specific bleaching, mortality, and spatial abundance patterns have the potential to broadly affect ecosystem structure and functioning (Hughes et al, ; Hughes, Kerry, et al, ; Pandolfi, Connolly, Marshall, & Cohen, ; Stuart‐Smith, Brown, Ceccarelli, & Edgar, ). While both Pocillopora and Porites experienced severe bleaching, bleaching severity was only linked to immediate mortality of Pocillopora (Figure d).…”

Coral reef ecology in the Anthropocene

“…Globally, human‐induced warming of the ocean is resulting in increasingly frequent mass coral bleaching events (Hughes, Anderson et al, ) that are transforming coral assemblages (Hughes, Kerry et al, ) and in some cases causing regime shifts to fleshy macroalgae (Graham, Jennings, MacNeil, Mouillot, & Wilson, ). In combination with human‐induced ocean acidification (Albright et al, ), these shifts in benthic composition have broader ecosystem effects, from compromising the growth of reef structures (Perry & Alvarez‐Filip, ; Perry et al, ) to changing the diversity, abundance and behaviour of other reef‐associated organisms (Keith et al, ; Richardson, Graham, Pratchett, Eurich, & Hoey, ; Stuart‐Smith, Brown, Ceccarelli, & Edgar, ). Hence, myriad interconnected human drivers are rapidly changing the structure and function of reefs (Pendleton, Hoegh‐Guldberg, Langdon, & Comte, ).…”