The relentless march of mass coral bleaching: a global perspective of changing heat stress

The global coral bleaching event of 2014-2017 resulted from the latest in a series of heat stress events that have increased in intensity. We assessed global- and basin-scale variations in sea surface temperature-based heat stress products for 1985-2017 to provide the context for how heat stress during 2014-2017 compared with the past 3 decades. Previously, undefined "Heat Stress Year" periods (used to describe interannual variation in heat stress) were identified for the Northern and Southern Hemispheres, in which heat stress peaks during or shortly after the boreal and austral summers, respectively. The proportion of reef pixels experiencing bleaching-level heat stress increased through the record, accelerating during the last decade. This increase in accumulated heat stress at a bleaching level is a result of longer stress events rather than an increase in the peak stress intensity. Thresholds of heat stress extent for the three tropical ocean basins were established to designate "global" events, and a Global Bleaching Index was defined that relates heat stress extent to that observed in 1998. Notably, during the 2014-2017 global bleaching event, more than three times as many reefs were exposed to bleaching-level heat stress as in the 1998 global bleaching

Climate variability and change: monitoring data and evidence for increased coral bleaching stress

Coral reefs live within a fairly narrow envelope of environmental conditions constrained by water temperatures, light, salinity, nutrients, bathymetry and the aragonite saturation state of seawater (Buddemeier and Kinzie 1976; Kleypas et al. 1999; Hoegh-Guldberg 2005). Their natural environment, at the interface of land, sea and the atmosphere, can vary quickly and potentially be stressful. Reef organisms have, over millions of years, evolved strategies to cope with occasional environmental disturbances (such as tropical cyclones). Given sufficient time between disturbances, damage or destruction would normally be followed by recovery and regrowth (Buddemeier et al. 2004). As documented in numerous scientific studies and reports, the world's coral reefs are "in crisis" as a result of direct local- and regional-scale human impacts on their environment. These impacts include overfishing, destructive fishing practices, changed land-use that increases sediment, nutrient and pollutant flows into reef waters, and poorly designed coastal development. This ecosystem degradation is largely occurring in the many tropical countries whose increasing populations are heavily dependent on coral reefs yet have insufficient resources to develop appropriate, sustainable management practices (Wilkinson 2004). Coral reefs are now confronted with additional global-scale stresses due to the introduction of enhanced greenhouse gases that are rapidly changing coral reefs' environmental envelope through both ocean acidification and increased thermal stress due to climate change (Hoegh-Guldberg et al. 2007)

Mapping crustal structure across southern Australia using seismic ambient noise tomography

The rocks of southern Australia record over three billion years of Earth’s evolution, but the basement geology is veiled by sediment. Geophysical data are needed to unveil the geology. The 2018–2022 Lake Eyre Basin and 2020–2022 AusArray SA seismic arrays expand seismic coverage in South Australia. In conjunction with permanent and preceding temporary arrays, we extracted Rayleigh wave dispersion data from ambient noise recordings at a total of 501 seismic stations spanning the transition from Precambrian to Phanerozoic Australia. These data were used to develop Rayleigh wave phase velocity maps of southern Australia at periods 3–20s, and in turn, a shear wave velocity model to 20km depth. At upper-crustal depths, low velocity structure tracks Phanerozoic sedimentary accumulations. The Moyston Fault, regarded as the boundary between the Delamerian and Lachlan Orogens, has an intermittent expression in the shear velocity model: it has no obvious expression at depths shallower than ~10km, but in the mid-crust is marked by a velocity contrast in southern Victoria and a velocity contrast tracing the southern edge of the Darling Basin in western New South Wales. An arcuate velocity contrast characterising the western edge of deep, sediment-filled troughs of the Darling Basin is a candidate for the transition from Precambrian to Phanerozoic crust. Fluid derived from neotectonic metamorphic devolatilization and/or remnant hydrated mantle is our preferred hypothesis for explaining seismicity and coincident seismic and conductivity anomalies in the mid-to-lower crust beneath the Ikara– Flinders Ranges. Our model suggests that the Olympic Dam and Carrapateena IOCG deposits reside above the margin of a mid-crustal low seismic velocity zone. We surmise that this might reflect past metalliferous fluid movement associated with the Olympic Cu-Au Province, akin to low reflectivity and low resistivity zones evident in 2D reflection seismic and magnetotelluric profiles, respectively.J.P. O, Donnell, S. Agrawal, C.M. Eakin, S. Thiel, K. Brand, A. Gorbatov, B. Goleb

Improvements to and continuity of operational global thermal stress monitoring for coral bleaching

Mass coral bleaching results from periods of elevated sea temperature. Satellite monitoring of thermal stress has enhanced the capacity for the management of coral bleaching events worldwide. Satellite-based monitoring tools provide reef managers with cost-effective observations of temperature conditions to monitor the risk of bleaching and to target in situ observations in areas under stress. This paper describes improvements to satellite remote sensing products from NOAA's Coral Reef Watch to enhance product coverage and to correct identified errors in the production of coral reef-specific metrics for thermal stress. In addition, threats to the operational production of the thermal stress metrics are considered and a contingency plan is described to ensure continuity of operations

Endangered Species Act listing: three case studies of data deficiencies and consequences of ESA 'threatened' listing on research output

Determining whether a species warrants listing as threatened or endangered under the U.S. Endangered Species Act depends on the government's assessment of the species' extinction risk, usually in response to a petition. Deciding whether data are sufficient to make a listing determination is a challenging part of the process. We examined three case studies involving corals. A petition for deep-sea corals was rejected for full status review of the species, based on insufficient information on population trends and threats. Information on threats for 82 tropical corals was sufficient to propose listing of 66 species. Significant population declines and identified threats resulted in listing two Atlantic Acropora corals as 'Threatened'. There was no decrease in journal publication rate on the Acropora species after that listing, and no decrease in research permit applications in marine protected areas. However, the effects of listings on research that might help to sustain or recover species remains largely unknown