Coral bleaching threat persists in Southern Hemisphere

Uptick in tropical cyclones intensifies impacts, hampers recovery

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A recent update from NOAA’s coral watch program shows that many reefs in the Southern Hemisphere face potential bleaching events in the next several months.

Staff Report

Along with the widely reported bleaching threat from over-heated oceans, coral reefs in many parts of the world also may have to cope with intensifying tropical storms, which could make it even more difficult for them to survive the Anthropocene.

New research published in the journal Global Change Biology looked at whether predicted increases in cyclone intensity might change the nature of coral reefs, using the Great Barrier Reef as a test case with reef data going back to 1996, as well as information gathered during recent tropical cycles. The study found that tropical cyclones between 2009 and 2014  caused record destruction of corals.

Then they modeled future impacts, with grim findings. Tropical storms strong enough to cause severe reef damage could happen every 25 years by 2100, presenting a significant threat to reefs independent of bleaching caused by global warming.

The implications extend beyond the projected coral and fish losses through associated decreases in biodiversity, increased vulnerability of coral reefs to long-term degradation and associated flow-on effects to social and economic services.

Meanwhile, scientists with NOAA’s coral reef watch program are warning that there’s widespread danger of bleaching this year even after last year’s powerful E Niño has faded. Areas at risk of significant mortality include  the Northern Cook Islands, Southern Cook Islands, the Samoas, Wallis & Futuna, Northern Tonga, Southern Tonga, the Society Archipelago, and the Austral Islands in the next 1-4 weeks. Alert Level 1 bleaching conditions are also expected in the Tuamotu Archipelago in the next 1-4 weeks and in Tuvalu in the next 5-8 weeks.

For now, Hawaii’s reefs are out of hot water, according to the NOAA update. Cooler waters have returned to  the Phoenix Islands (Kiribati), but extremely warm water temperatures starting in June 2015 have already killed most of the corals in that area. The high bleaching heat stress in Kiribati was tied to the very strong El Niño that dissipated in late 2016, but whose effects will last for many months in the southern hemisphere. It is estimated that only 1-5 percent of Kiribati’s reefs will survive and recover from this severe bleaching heat stress event.

The severe heat stress in East Asia also has dissipated,  but continues  in parts of the Coral Triangle, where a significant coral bleaching is expected in the next few weeks in Papua New Guinea and the Solomon Islands.

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