HONOLULU — On the map of the main Hawaiian isles, colored dots denoting the extent of bleached corals cover the north and south sides of Kauai, surround all of Oahu and blanket the west sides of Maui and Hawaii island.
Upon closer view there are also dots on smaller islands, including Niihau, Molokai, Lanai and Kahoolawe.
The dots — red for severe, orange for medium and yellow for light — are pinpointed on a map by hundreds of citizen scientists who are for the first time helping researchers track this year’s coral bleaching event in real time, in tandem with satellite imagery.
The map, a collaborative project by the state, the National Oceanic and Atmospheric Administration, and Arizona State University’s Center for Global Discovery and Conservation Science, offered researchers insight into the bleaching event’s progression from August to October.
“The dots started out as yellow,” said Greg Asner, director of ASU’s GDCS. “People were logging light bleaching, yellow, and in most recent weeks they’re hitting the red button, severe. It was a progression.”
Asner explained that even as ocean temperatures begin cooling, corals are still reacting to warmer-than-average summer temperatures, so bleaching is still occurring, putting new dots on the map.
These citizen scientist reports help inform researchers of what areas to measure, according to Asner, who said hundreds participated.
“It’s the citizen science in this process that directed us,” he said. “We would actually fly to the places where people were reporting, get in the water and not only verify reports, but do the more detailed, professional measurements.”
Those measurements include the severity of bleaching as well as what species of coral were involved and how fish populations responded. Satellite tracking, meanwhile, revealed “hot spots” of bleaching across the isles.
State and federal officials reported that coral bleaching was widespread across the state this summer but not as severe as previous events in 2014 and 2015.
Scientists had been alarmed when NOAA in August noted ocean temperatures in Hawaii were trending higher than in 2015. In September, NOAA noted they were 3.5 degrees Fahrenheit higher than typical for the month.
Still, as much as half of live coral bleached in the most heavily affected areas of the state, officials said.
When corals are stressed by changes in conditions, including temperature, they expel a symbiotic algae living in their tissues — zooxanthellae — which causes them to turn white. Corals can survive bleaching, but the chances of recovery decline the longer the stressors continue.
Survey teams found signs of heavy bleaching by Anini Boat Ramp on Kauai, as well as on the West and Windward sides of Oahu, near West Maui and at Molokini, according to David Delaney, coral planner for the state Division of Aquatic Resources.
Heavy bleaching occurred on Oahu at Makua Beach, Yokohama Bay and Ko Olina, as well as around Daniel K. Inouye Airport, where over 75% of some corals, mostly cauliflower corals, had bleached.
On Maui state teams found heavy bleaching of over 75% in West Maui. In September they reported, where roughly 50% of the corals are made up of the species Montipora capitata, as well as along the south shore, from Makena to Maalaea. On Molokai about 50% of sites around Kamalo Harbor experienced moderately heavy bleaching.
For Hawaii island, corals along the Kona Coast were most affected this year, according to officials. An average of 40% of live coral bleached in many survey locations in the area, which suffered from heavy bleaching in 2015, resulting in high mortality.
The bleaching off of Ka’u was severe, with up to 80% of the coral in the area bleached.
What was also new this year, according to Asner, was the depth at which coral bleaching occurred in the Hawaiian Islands. In 2015 most of the warm water was on the surface of the ocean, but this time it affected corals at depths of up to 70 feet.
“That’s a new phenomenon in Hawaii,” he said. “I’ve seen it in French Polynesia and other places, but that was a new one in Hawaii.”
Anticipating the widespread bleaching, the state this summer launched highlighting that residents and tourists alike can take to help reduce stressors on corals, vital to the state’s ecology, culture and economy. Tour companies are encouraged to share the pledge with their guests before heading into the water.
While this summer’s bleaching event was not as severe as feared, the growing concern is in the frequency of these events in the future, said Delaney, due to climate change.
“The intensity wasn’t as intense, but the frequency is growing,” said Delaney. “We used to have a lot of time in between bleaching events, but now they’re becoming far more frequent and we don’t have time for corals to recover.”
Models show that in future decades bleaching could become an annual event, he said, offering corals even less time to recover.