Japan Times: Tourism Takes Its Toll on Coral

The Japan Times:  Margaret Mars Brisbin is a Ph.D. candidate in marine science at the Okinawa Institute of Science and Technology (OIST), which probably brings to mind frolicking dolphins and giant schools of tropical fish. But Brisbin’s focus is much, much smaller: marine microeukaryotes, the photosynthetic organisms that make coral possible. In a healthy reef, these microscopic symbionts live inside hard corals, providing the energy that powers their growth. In an unhealthy reef, stressed corals expel their tiny residents, resulting in bleaching and, eventually, death.

In 2015, Brisbin came to Okinawa to start work on her Ph.D., attracted by the research possibilities offered by the nearby reefs and long warm-water diving season. “My very first weekend on island, I went diving at a local dive site, Maeda Point or Blue Cave, but was relatively shocked at what I saw,” she says. “The divers and snorkelers showed absolutely no concern for the flora and fauna of the reef. Everywhere I looked, people were stepping on the reef and kicking and crushing fragile coral colonies.”

The United Nations Environment Programme recommends a dive site be limited to 6,000 visitors per year to remain pristine, but based on her observations, Brisbin estimates well over 1,000 people visit Maeda Point per day during the peak season.

One component of the Ph.D. program at OIST is a group project that benefits the community, so Brisbin suggested doing surveys to see what this heavy use and lack of good practices was doing to the reefs. “I just thought that we should, rather than just talking about (how people use the reefs) and being judgmental, we should measure it and see if it’s really having an effect or not. And so I pitched that idea to the other students in my class, and that got people to sign up.” This was the beginning of Oki Coral Watchers, a group monitoring the health of Okinawa’s reefs.

In that first year, the focus was on getting robust data to form a baseline for reef health. The group selected four sites for weekly surveys on a spectrum of use. Maeda Point, as the most popular dive site in Okinawa, was an obvious choice. In addition, they talked with local dive shops to select sites at medium and low levels of use, eventually settling on Mini Dream Hole, which can only be reached by boat, and Horseshoe Beach, where strong currents generally restrict use to experienced divers. Finally, consulting with the marine science department at OIST, they selected a place off distant Sesoko Island as a control site with no tourism.

From March to November, the team went out every weekend to survey one of the sites. This involved stretching a 50-meter transect across the same section of the reef each time and evaluating the amount, type and health of the coral it crossed. To gauge health, they used a color comparison card developed by CoralWatch, a citizen science project based at the University of Queensland. The CoralWatch card has a gradient on each side of a common coral color, with each shade corresponding to the amount of those symbiotic microeukaryotes present. The higher the color saturation, the healthier the coral. Users simply hold the card next to the coral and then match the color to get a rough estimate of health.

In addition to looking at the corals, the group collected data on the number of people using the sites. To control for other factors that could affect reef health, they tested water samples for acidity, nitrogen, phosphorous, dissolved oxygen, biological oxygen demand and the presence of coliform bacteria. They also installed sensors that measured the temperature and light intensity every two hours to control for variation in the environment between sites. Once the data was compiled, it was clear that tourism takes a toll on reefs. The more popular a site, the fewer hard corals it had and the less diverse they were. Delicate branch and plate corals gave way to more robust boulder corals, leaving the reef with less 3-D complexity, or fewer nooks and crannies to attract fish and other denizens.

Surprisingly, one thing they didn’t observe in the 2015 surveys was bleaching at any of the sites. That year, an unusually active typhoon season and lower summer temperatures kept the water around Okinawa from exceeding 30 degrees for a prolonged period of time, so the corals were relatively healthy. However, in the years since, the global trend of rising temperatures has hit Okinawa hard. The Environment Ministry reported that 91.4 percent of Okinawa’s Sekisei Reef, the country’s largest, bleached in 2016. In 2017, the numbers were better, but still close to half of the reef bleached and died, a situation the ministry calls critical.

“I feel like in a lot of ways it was good luck to have our big survey the year that didn’t have bleaching, but I also feel like it was kind of bad luck because we really want to use this project to raise awareness about coral conservation. The data that we have from our baseline is that there wasn’t any bleaching that year and I feel like it’s not representative of what’s happening this year or last year,” says Brisbin. “The last two years there’s been a lot of bleaching, a lot of cover, a lot of death, so it’s important to keep documenting it, but it’s also good that we have this baseline to show how much it’s changed over the last two years.”

Since the completion of those intensive surveys, Oki Coral Watchers has continued to do data collection using the CoralWatch methodology and has been working to get members of the public involved. They’ve started a Facebook group under the name OkiCoralWatchers to foster a community among surveyors and help beginners get started.

Doing a survey is simple enough that children and complete novices can jump right in. People can order the waterproof color card from www.coralwatch.org free of charge. Then, they simply select 20 corals at random while diving, snorkeling or walking tide pools and use the card to survey their health. “The CoralWatch surveys don’t require you to do assigned taxonomy. It’s just the shape of the colony,” explains Brisbin. The method groups corals into four rough categories: branching, plate, boulder and soft. The user decides which a particular coral is and evaluates the health using the color gradient. CoralWatch also provides a free mobile app to upload survey results and maintains a global database of real-time results anyone can use. Scientists can use the crowd-sourced data to study global ocean health, while policymakers can use it in crafting legislation.

Brisbin says she wants people to come and enjoy Okinawa’s natural attractions, though she hopes they will be mindful of safety, both their own and the reef’s. And perhaps while they are enjoying their vacation, visitors can also take a little time to help out with a quick survey. While popular reefs in the Caribbean and Australia have hundreds of regularly updated surveys covering a broad area, Okinawa still has relatively little data, so Oki Coral Watchers would like to get more people involved, particularly considering the island prefecture’s critical location.

“Okinawa is at the very northern edge of the span of coral reefs and so for a lot of the really big bleaching events, Okinawa has not had as bad a bleaching as the Great Barrier Reef, because it’s a little bit cooler here. In a lot of ways, it’s … a little bit of a reservoir for some of the species where they can hold on in these more northern ranges,” says Brisbin. “Okinawan corals are in danger and it matters for the larger coral existence.”