Unprecedented Mass Bleaching and Loss of Coral across 12° of Latitude in Western Australia in 2010–11

Abstract

BackgroundGlobally, coral bleaching has been responsible for a significant decline in both coral cover and diversity over the past two decades. During the summer of 2010–11, anomalous large-scale ocean warming induced unprecedented levels of coral bleaching accompanied by substantial storminess across more than 12° of latitude and 1200 kilometers of coastline in Western Australia (WA).Methodology/Principal FindingsExtreme La-Niña conditions caused extensive warming of waters and drove considerable storminess and cyclonic activity across WA from October 2010 to May 2011. Satellite-derived sea surface temperature measurements recorded anomalies of up to 5°C above long-term averages. Benthic surveys quantified the extent of bleaching at 10 locations across four regions from tropical to temperate waters. Bleaching was recorded in all locations across regions and ranged between 17% (±5.5) in the temperate Perth region, to 95% (±3.5) in the Exmouth Gulf of the tropical Ningaloo region. Coincident with high levels of bleaching, three cyclones passed in close proximity to study locations around the time of peak temperatures. Follow-up surveys revealed spatial heterogeneity in coral cover change with four of ten locations recording significant loss of coral cover. Relative decreases ranged between 22%–83.9% of total coral cover, with the greatest losses in the Exmouth Gulf.Conclusions/SignificanceThe anomalous thermal stress of 2010–11 induced mass bleaching of corals along central and southern WA coral reefs. Significant coral bleaching was observed at multiple locations across the tropical-temperate divide spanning more than 1200 km of coastline. Resultant spatially patchy loss of coral cover under widespread and high levels of bleaching and cyclonic activity, suggests a degree of resilience for WA coral communities. However, the spatial extent of bleaching casts some doubt over hypotheses suggesting that future impacts to coral reefs under forecast warming regimes may in part be mitigated by southern thermal refugia.

Assessing the drivers of spatial variation in thermal forcing across a nearshore reef system and implications for coral bleaching

“…5B). Not surprisingly, this period of historically elevated temperatures led to the mass bleaching of around 30% of the coral cover within Coral Bay (Moore et al 2012). Although this period of extreme offshore temperatures continued well into April, temperatures inside Coral Bay switched from being predominantly higher than offshore SST to being predominantly lower than offshore SST by late March (Fig.…”

“…This was best demonstrated by a historically unprecedented ''marine heat wave'' that formed along Ningaloo Reef and much of Western Australia in early 2011 due to particularly strong La Niñ a conditions across the Indo-Pacific (Feng et al 2013). The mass bleaching associated with this event (Depczynski et al 2012;Moore et al 2012) clearly demonstrated how global climate patterns could affect coral communities within an individual reef system through regional climate-forcing mechanisms.…”

Stability of marine phytoplankton communities facing stress related to global change: Interactive effects of heat waves and turbidity

“…Heat waves, in this context, are defined as a period of at least three to five days during which mean or maximum temperature anomalies were at least 3-5°C above normal (Hobday et al, 2016;Meehl and Tebaldi, 2004). Such heat waves affect marine ecosystems with respect to invertebrate, fish and macroalgal mortality, and the occurrence of algal blooms, as events in the North-western Mediterranean in 2003 (Garrabou et al, 2009) and heat waves in 2011 along the western Australian coast (Moore et al, 2012;Rose et al, 2012) have shown.…”

Validation of Reef-Scale Thermal Stress Satellite Products for Coral Bleaching Monitoring

“…Throughout this period, the U.S. National Oceanic and Atmospheric Administration's Coral Reef Watch (NOAA CRW) program developed and released coral-specific satellite-based tools and successfully monitored thermal stress causing mass bleaching events around the world [1][2][3][4][5][6][7][8]. These products have been instrumental in aiding reef managers and other stakeholders to prepare for and respond to coral bleaching events.…”