Three months after Hawaii’s corals endured the worst bleaching on record, state officials say island reefs could face conditions later this year that could produce even greater damage.
While the good news is that most of the coral colonies that whithered in Hawaii waters late last year are showing signs of recovery, officials warned Thursday that a second and even more severe bleaching episode could act as a knockout blow to some vulnerable corals.
"It seems like we were lucky this time around," said Anne Rosinski, a marine resource specialist with the state Department of Land and Natural Resources. "Our corals are pretty resilient. They’re able to bounce back. But just like with people, if you keep mounting on all these stresses, eventually they’re not going to make it."
Bleaching is a stress response to unusually warm water. Corals lose algae and color from their tissue, making them appear snow white and leaving them in a weakened state that makes them vulnerable to disease and possible mortality, depending on severity. It can take weeks to several decades for a coral reef to recover.
State Division of Aquatic Resources officials, speaking to reporters at Heeia Kea Small Boat Harbor in Kaneohe, said water temperatures are predicted to become dangerously warm for corals again in 2015, with El Nino conditions expected to develop.
Bleaching is expected from July to October, the time of highest sea temperatures. On a global scale, coral bleaching is expected to worsen in the coming decades as the climate changes, scientists say.
As for last year, not only did the main Hawaiian Islands experience their worst bleaching event on record, according to the National Oceanic and Atmospheric Administration, but a record level of heat stress was observed in the ocean surrounding the Northwestern Hawaiian Islands.
In the main islands, sea temperatures spiked at 86 degrees, and bleaching was seen in mostly shallow water from Kauai to Hawaii island. But the worst of it occurred off Windward Oahu, where 80 percent of the dominant corals experienced bleaching, Rosinski said.
"Just the past couple of weeks, we have seen the color returning to the corals," she said. "When we went out in October, it looked like a coral graveyard. Everything was white and gray and very dead-looking. And when we went out a couple of weeks ago, the color was back. You definitely can see it."
Of the 50 sites tagged in Kaneohe Bay, 12 percent of the coral colonies died. Some of the victims succumbed to a combination of factors, including episodes of freshwater flooding and boat propeller marks.
Why was Kaneohe Bay hit so hard?
"It’s like a bathtub," Rosinski said. "When the bathtub heats up, the water will flush out a lot more slowly than a place like Kauai where there’s a lot of wave action."
Since October, sea temperatures have cooled by about 5 degrees.
State aquatic biologist Stacy Bierwagen said, "I think overall the general consensus has been that everything in Kaneohe Bay that is recovering is going to stay recovered at this point. What we are wondering about in the future is if the corals that have recovered will do so again after the next bleaching event, or will it be worse?"
Rosinski said officials plan to meet with conservation groups to outline a plan for assessing damage from the upcoming bleaching season. A multi-agency response team will assess the severity and extent of the bleaching.
"Kaneohe Bay is a very unique place, and it supports a lot of life, so we’re definitely trying to preserve that," she said.
Last year, officials received more than 100 reports from citizens in the field as well as some 60 photographs showing bleaching across the state.
"We were really fortunate to get reports from the public," Rosinski said. "Having those reports was critical. It allowed us to prioritize where we were going."
Anyone who observes bleaching this year can report it and send photographs to www.eorhawaii.org.
"Everyone has a (camera) these days," she said, "Just take a picture and send it to us. It really does help us."
