Environment

Second consecutive year of severe coral bleaching in Hawaii

Hawaii's reefs are already reeling from their worst coral bleaching event in recorded history in 2014, when record warm ocean temperatures caused 50 - 70% of the corals sampled in Northeast Oahu's Kāneʻohe Bay to bleach. When the sea surface temperature is 1°C warmer than the highest monthly mean temperature corals usually experience, coral polyps will expel the symbiotic algae that live in their tissues, exposing the white skeleton underneath, resulting in a white "bleached" appearance. Death can result if the stress is high and long-lived. In Hawaii's waters, corals cannot tolerate water temperatures above 83°F (28.3°C) for multi-week periods without suffering bleaching. Corals typically recover from mild bleaching, gradually recovering their color by repopulating their algae. However, if the bleaching is severe or prolonged, individual polyps or whole colonies will die. With Hawaii likely to undergo a second consecutive year of record warm waters and coral bleaching in 2015, widespread mortality in many of Hawaii's coral reefs is possible, particularly around the Big Island.