High regional and intra-generic variation in susceptibility to mass bleaching in Indo-Pacific coral species

Abstract

AimMass bleaching is a major threat to reef-building corals and the ecosystems they underpin. Here, we identified regional variation in the nature of this threat in terms of the bleaching-susceptibility of individual coral species on some Indian Ocean and Pacific Ocean reefs.Location22 sites in the central Great Barrier Reef, Australia (GBR) and 30 sites in the central Maldives Archipelago (MA).Time period2002 for the GBR and 2016 for the MA.Major taxa studiedCorals (Order Scleractinia).MethodsFollowing marine heat-wave conditions, timed in-situ surveys were used to record bleaching responses (tissue colour) of large samples of individual coral colonies. Responses of 106 shared species were analysed for sites with similar levels of temperature stress, depth of occurrence and mortality. In each region, phylogenetic mixed models were used to partition the effects on responses of species of deep-time phylogeny, contemporary history and local-scale, among-site variability.ResultsRelative susceptibility to bleaching varied widely between regions: only 27 of the 106 shared species were in the same quartile for relative susceptibility in both regions. Few species were highly susceptible in both regions. Closely related species varied widely in their individual susceptibilities. Phylogenetic effects were moderate in both regions, but contemporary phenotypic effects indicative of recent evolution and acclimatization were greater in the MA, consistent with a stronger history of recent bleaching.Main conclusionsThe high regional and intra-generic variation in coral bleaching-susceptibility described here suggests there may be important differences in the extent to which these Indian and Pacific Ocean coral populations are exhibiting responses to deep-time evolutionary changes on the one hand, versus recent adaptation, on the other. There is a concerning scarcity of this type of data, by which coral species most at risk from bleaching in particular regions may be more accurately identified.

Screening for climate adaptative loci using seascape genomics resolves phenotypic variation in heat tolerance of the coral Acropora millepora.

“…In these natural settings, correlations between SST and coral bleaching are generally found from 4.0 Degree Heating Weeks (DHW) and widespread bleaching is observed from 8.0 DHW 91 . Although bleaching thresholds vary widely across genera and species 14 , Acropora species are generally considered more vulnerable to high temperatures because of their branched morphology, reduced tissue thickness and low mass-transfer rates 71 . In this study, we used long-term moderate levels of heat stress to reproduce a natural thermal anomaly and investigate variation in heat tolerance among conspecific corals from the same reef.…”

“…However, coral bleaching is rarely uniform in time, space and intensity as numerous biotic and abiotic factors drive the response of coral colonies to heat stress. Bleaching susceptibility varies among geographical regions 13 , species 14 , morphotypes 15 , thermal history 16 and environmental conditions (e.g. hydrodynamic flow 17 , nutrient enrichment 18,19 and light irradiance 20 ).…”

Climate adaptive loci revealed by seascape genomics corroborate phenotypic variation in heat tolerance of the coral Acropora millepora

“…For instance, 3.3 DHW led to bleaching in 10 Acropora species in a reef from Okinawa 129 and 4 DHW caused bleaching and > 75% coral cover decline in Acropora species on the GBR 5,130 . Although there is substantial intra-generic variation, a recent assessment of Indo-Paci c species vulnerability to climate change ranked A.millepora as medium high susceptible to mass bleaching 15 . Notably, two studies on A. millepora response to arti cial heat stress reported an 82% decline in Symbiodiniaceae concentrations and shifts in antioxidant systems after 6 days at 32°C (~ 4.2 experimental DHW (eDHW) 131 ) 74 as well as high bleaching levels after 8 days at 31°C (~ 4.5 eDHW) 132 .…”

“…Therefore, the Intergovernmental Panel on Climate Change predicts that 70-90% of global coral cover will be lost by 2100 under a 1.5°C warming scenario 13 . However, coral bleaching is rarely uniform in time, space and intensity as heat stress responses vary among geographical regions 14 , species 15 , morphotypes 16 , thermal history 17 and environmental conditions (e.g. hydrodynamic ow 18 , nutrient enrichment 19,20 and light irradiance 21 ).…”