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Hawaii’s corals appear to have been spared this summer from another mass bleaching, a stress response caused by warmer waters that has ravaged reefs in recent years.
But they haven’t been so lucky with another emerging threat.
An invasive algae called leather mudweed is rapidly spreading in places where it had been mostly removed and has been found in new areas around Oahu, according to a site survey last month by the state Department of Land and Natural Resources Division of Aquatic Resources.
“It’s really kind of scary,” said Bruce Anderson, who heads the agency.
It’s unclear what the plan of attack will be at this point but the options are limited.
Managing the roughly 410,000 acres of living reef in the Main Hawaiian Islands is a perpetual challenge. There are technical hurdles in some cases, such as removing the mudweed, and political barriers in others, like establishing marine protected areas.
Many reefs in the state — especially those around Oahu, by far the most populous island with 1 million residents and more than 5 million visitors annually — are severely degraded from overfishing, polluted runoff and global factors that are causing a warmer, more acidic ocean.
The reefs play a critical role, such as protecting coastal communities from storm surges and providing homes for fish that people depend on for food and tourism.
DLNR, for a time, was able to get a handle on a mudweed infestation in Maunalua Bay on the eastern side of the island with the help of nonprofits and a $3.4 million grant from the National Oceanic and Atmospheric Administration.
“It’s really kind of scary.” — State Aquatics Resources Administrator Bruce Anderson, on the leather mudweed infestation.
Known as “The Great Huki,” volunteers pulled 3 million pounds of leather mudweed in 2010. Removing it by hand was incredibly labor intensive, Anderson said.
Unfortunately it has grown back. Dozens of volunteers returned to the bay’s shallow waters this summer, pulling thousands of pounds of the leather mudweed and another invasive, a prickly seaweed called gorilla ogo.
Now the aggressive mudweed is also at Bellows on Oahu’s windward side, Barbers Point on the south shore and in the northern portion of Kaneohe Bay. It’s also at depths of up to 100 feet, which had not been seen before. The algae thrives in degraded marine environments, Anderson said.
The invasive algae blankets reefs, depriving the corals from the sunlight they need to survive. It also outcompetes native algae and seagrasses while trapping sediment to form a muddy layer on the sand, according to the University of Hawaii’s Botany Department.
Scientists aren’t sure how the mudweed got to Hawaii. It was first discovered in 1981 on the leeward shore of Oahu.
It was University of Hawaii physiologist Celia Smith who found it this summer near Mokolii Island in Kaneohe Bay during a study sponsored by the Smithsonian Institute, called the MarineGeo Hawaii survey. The study will identify and document all aquatic life in Kaneohe Bay for research and management purposes, Anderson said.
Over the past several years, DLNR has been able to beat back two other types of invasive algae in Kaneohe Bay by deploying a one-two punch.
Elkhorn sea moss and smothering seaweed were introduced into the bay in 1974 with the intention of extracting carrageenan, a thickening additive used in milk and other foods. After that failed experiment, it started to take over in certain areas.
After sucking up much of the algae, DLNR started putting native sea urchins in the bay in 2011 to eat more of it and keep it down. By 2016, divers had placed more than 300,000 urchins, all grown in a hatchery on Sand Island.
Anderson said it’s been a “great success” and is being considered as a management tool for other areas. He said there’s some evidence that urchins might also eat the mudweed but it hasn’t been verified. The algae would have to be removed first, too.
Other options, like using the “super sucker,” won’t work for the mudweed. Anderson said it would vacuum so much sediment that it would clog the pipe and incidentally suck up things that shouldn’t be removed.
Ultimately, Anderson said, the best management strategy is reestablishing and maintaining healthy reefs that have substantial herbivorous fish populations to keep the algae down.
That’s as important in fighting leather mudweed and other invasive algae as it is for dealing with coral bleaching.
Hawaii’s reefs suffered their worst bleaching on record in 2014 and 2015. Up to 85 percent of corals in some areas of the Big Island were lost, and Kauai, Maui and Oahu were also hit hard.
“This was really an unprecedented, devastating impact on the state,” Anderson said.
Last year was not as bad. But he said Hawaii needs to be ready because coral bleaching will undoubtedly reoccur.
“It’s not a question about whether but when,” Anderson said, adding that Hawaii seems to have “dodged a bullet” this summer.
NOAA’s Coral Reef Watch forecast for the next four months places most of the Main Hawaiian Islands under “watch” status. That means the waters have been warmer than they have on average over the past 30 years. But the waters aren’t quite warm enough to warrant a “warning” level that signifies imminent bleaching, which is what most of the Northwestern Hawaiian Islands are experiencing.
Most of the bleaching in 2014 and 2015 began in September and continued into October before starting to subside.
“If it’s going to happen this year, it’s going to happen really soon,” said Tom Oliver, a research scientist who works with NOAA’s Pacific Islands Fisheries Science Center. He’s the ocean acidification program manager and works on climate change and coral reef issues.
“It’s now becoming a new normal,” he said.
Oliver worked with Anne Chung and other scientists with the Division of Aquatic Resources to develop the state’s first-ever Hawaii Coral Bleaching Recovery Plan, published in May.
They reviewed hundreds of published scientific papers on coral bleaching and talked to researchers from around the world about what the state could do in response.
The plan ranks the list of management actions that can be taken, such as reducing sediment runoff, enhancing enforcement of existing rules and better managing certain herbivorous fish.
When corals bleach, algae can take over and prevent the reefs from recovering because the polyps can’t settle and grow. Parrotfish, or uhu, have been found to be a key species that eats the algae.
Anderson said DLNR officials are looking at new rules to help ensure there are sufficient parrotfish, which could take the form of bag limits or even outright bans on fishing for uhu in some places.
He said DLNR will work to get the proposed parrotfish rules out in the “near future.” That will start the six-month to yearlong rule-promulgation process that includes public hearings and approvals from the state land board and eventually Gov. David Ige.
“One size doesn’t fit all,” Anderson said. “Management measures that might be appropriate for Hawaii Kai might not be appropriate for West Hawaii, and vice versa.”
State officials are also working on plans for what to do with the research from places like the Hawaii Institute of Marine Biology, which is under the direction of Ruth Gates.
They are trying to help decide where the “super corals” that scientists are breeding to be more resistant to climate change might have the best chance of surviving.
Anderson said transplant experiments have had limited success in Hawaii but are worth trying.
“The future is really going to be in better managing the marine areas to let nature take its course and allow the proliferation of herbivores that naturally help coral reefs recover,” he said.
Other scientists at the institute are conducting their own coral experiments in response to climate change that they hope are used in management strategies.
Ku‘ulei Rodgers, who has been the principal investigator of the Coral Reef Ecology Lab since 1993, is researching how corals are acclimating to the changing environment.
“There’s going to be winners and losers in a warmer, more acidic ocean,” she said. “Corals will be among the losers.”
Part of the management strategy needs to be establishing a network of marine protected areas where no fishing is allowed, Anderson said. It was the top-ranked management action in the Coral Bleaching Recovery Plan.
But he said the “political viability” of doing that, given pressures from the fishing industry and other ocean users, makes that a “longterm solution” that will take time to happen.
Much of the work will also come down to funding from the Legislature, he added.
“I’m cautiously optimistic the public will see this as a serious threat and be willing to do something to change to help the reefs and health of our ocean,” he said. “Everyone loves the ocean and appreciates how important it is to our lives and lifestyle here in Hawaii. That’s the best thing we’ve got going right now.”
Bob Richmond, who heads the Kewalo Marine Laboratory, is working with other scientists to develop tools to help managers in Hawaii and beyond understand precisely what is harming the reefs — whether that’s runoff, invasive species, diseases or the effects of climate change.
He recounted the incredible declines in coral coverage that he’s seen over the past 43 years of work.
Richmond recently went back to one of his first reef sites in the Virgin Islands, at a protected national park off of St. Croix, where he started studying in 1974. There was 80 percent coral cover at the time.
Five years ago, it was 5 percent coral cover, he said, and instead of schools of fish he found one snapper about three inches long and everyone got excited about it.
“I just went back to the room and cried,” Richmond said. “I just couldn’t believe in my own lifetime I’d see that amount of loss of an incredibly precious ecosystem.”
Gates, Richmond and other scientists recognized that the solutions need to fit the place.
In Hawaii, there are about 30 species of corals whereas the Great Barrier Reef has hundreds. And the use of reefs is different. In Hawaii, the reefs are used more for recreation. Other places use them almost exclusively for food. In some areas, it’s a combination.
Scientists are building a “community of players” — engineers, biologists, business leaders and government officials — who will take action to solve the problem creatively and collaboratively, Gates said.
“It’s really an exciting time,” she said.
Gates said the end goal is translating the work being done in Hawaii to the hundreds of thousands of people who are also working in places adjacent to reefs and coming up with the best management solutions. And each community, she said, should develop its own plans that are suited to that particular place.
“We might not think so much about food security here in Hawaii now because many of the reefs have been completely fished out,” Gates said. “But coastal security is a huge issue, so we might decide to target our adaptation to make sure that we maintain structural integrity on that reef.
“It may mean we have to make some pretty difficult decisions,” she said.
Read the state’s Coral Bleaching Recovery Plan below.