Utilising an innovative mixture of advanced, high-resolution aerial mapping technology and geotag information data-scrapped from social-media giant Instagram, researchers from Arizona State University and Princeton University recently discovered a “strong correlation” between overtourism and coral reef degradation. The research highlights not only the importance of understanding the intricate relationships between coral reef health and tourism but also how essential high-resolution data is in determining how influential local stressors affect coral reef health. Furthermore, the study also touches upon the subject of Hawaiian water quality and pollution, a topic that Greg Asner, director of the ASU Center for Global Discovery and Conservation Science in the Julie Ann Wrigley Global Futures Laboratory and co-author of the paper, suggests should be taken more seriously in light of Hawaii’s limited wastewater-treatment infrastructure.

Regardless of where they are on the planet, coral reefs are universally beloved for their vibrant colours, their beautiful shapes, and their incredibly alien-like, awe-inspiring appearance. Coral reefs are so prized by the global community that the Great Barrier Reef, the largest coral reef on the planet, is considered one of the world’s seven natural wonders, and is diligently conserved by the Australian government through funding equivalent to billions of dollars each year.

As beautiful as coral reefs are, their conservation is not solely due to their attractive appearance. According to the National Ocean and Atmospheric Administration (NOAA), coral reefs support approximately 25% of all marine life that live within the Earth’s oceans. They are known as foundational or architect species, providing homes for an incredibly biodiverse ecosystem of oceanic organisms.

Not only that, coral reefs provide food and income for hundreds of millions of people across the planet, while also protecting shores from as much as 97% of potentially damaging waves and flooding. In truth, it is estimated that the benefits coral reefs provide are worth approximately US$11.9 trillion per year to the global economy.

coral reefs

So, If you plan to go coral reef snorkelling on your next vacation, you may want to reconsider how you interact with these cherished, essential organisms. They may look like rocks, but they are quite susceptible to damage– even by the average person.

In fact, recent research into coral reef degradation conducted by scientists from Arizona State University and Princeton University has brought to light the damages that the average person can cause to coral reefs, specifically the destructive nature of the seemingly innocuous, leisure activity of coral reef snorkelling, scuba diving, and tourism in Hawaii.

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‘Strong Correlation’ Between Overtourism and Coral Reef Degradation

Co-authored by Greg Asner, director of the ASU Center for Global Discovery and Conservation Science in the Julie Ann Wrigley Global Futures Laboratory, and leader of the largest coral reef monitoring program on the planet, the study in question found that there was a “strong correlation” between what has been dubbed  “overtourism” and significant coral reef degradation. 

“I know these reefs extremely well, so I’m careful to not say correlation is causation,” explains Asner. “But there was a really strong correlation – even I was impressed.” 

While wearing flight suits and oxygen masks, Asner and his colleagues accrued the data necessary for this study from as high as 18,000 ft (5,486 metres), utilising the most advanced airborne mapping technology available in the civil sector today. Known as the Global Airborne Observatory (GAO), the plane Asner and his team worked with – a highly modified Dornier 228-202 aircraft – was used to take  high-resolution images of the Hawaiian coastlines below. They then gathered the spectroscopic data from the pixels of each of those images to determine where the coral reefs were, and even the degree to which they had degraded.

 “A spectroscopic signature is far beyond the visual range. It’s in the near-infrared and it allows us to see the absorption and scattering of different molecules,” explains Asner. “We’re able to convert the molecular information into chemistry, and then the chemistry into ‘Is it a living coral or is it a dead coral?’” 

However, this was not the end-all to their study. 

“Ingredient number two is what my friends at Princeton brought to the table,” he adds.

The “ingredient” Asner is referring to are 275,724 public Instagram posts from the years 2018 to 2021, spread across 333 bays and beaches of the main Hawaiian islands. The posts were painstakingly data-scraped by Princeton researchers specifically for the geotag information associated with them. 

By combining the datasets harvested through both the GAO and Instagram, Asner and his colleagues were able to map out exactly where tourism hotspots were (measured as both overall and on-reef coastal tourism), and if those hotspots were centred around living coral or dead coral. As far as they could see from the data, tourists in Hawaii really liked coral, an obsession that could be causing serious problems for the health and well-being of these sensitive, living reefs. 

“They want to go to where there’s coral. And then where there’s a lot of tourism, there’s a lot of degraded coral,” says Asner. 

According to the study, of the hundreds of thousands of Instagram posts, 9,231 were associated with on-reef visitation. Specific on-reef visitation was associated with not only a higher hotel density, but also with higher quality of water and higher total and average coral reef coverage. This suggests that on-reef tourism is driven by both high-quality water and high-quality coral reefs. 

That being said, overall coastal visitations were found to be highest where accessibility was greatest – near hotels and roads – but also associated with greater levels of nearshore effluent, and thus, poorer quality of water.

The study also points out that visitation is highest where absolute live coral reef coverage is greatest, however, at the most popular sites, there is evidence that live coral coverage nearer to the shore is also being suppressed. These findings, as they state, suggest that areas with greater live coral coverage may attract more visitors, but the increase in visitation may also stifle the living coral – an effect that lessens the further the coverage is from land. 

Overtourism likely to Blame for Poor Coral Reef Health

As the study shows, the likely culprit behind coral reef degradation in Hawaii is tourism; or rather, overtourism.

“Tourism is good for the economy, but overtourism is bad for the environment,” says Asner. 

In the past, overtourism has often been associated with the negative impacts it can have on the quality of life for people–both tourists and residents. Today, the term has found new ground within the topic of conservation and sustainability as environmental scientists begin to notice how significantly the two are intertwined. Some, like Asner, are even seeing the consequences firsthand.

“We’re starting to see the effects of overtourism in specific locations. It’s not wall-to-wall yet. It’s not the entire coastline of all four of these islands, but it’s certain areas, certain bays, that attract a huge number of tourists. And I can tell you, I live near one that gets tourism monitoring, they say that sometimes they get 300 people per hour on only about 10 acres of reef,” he explains.  

According to the Economic Research Organization at the University of Hawaii, in 1960, Hawaii had a mere 300,000 visitors. By 1980, that number rose to approximately 3.9 million. By the start of the new millennium, the amount of visitors reached a staggering 7 million; today, the numbers are unprecedented. 

“Hawaii has ten and a half million visitors per year, and most of those visitors are on just four of the eight main Hawaiian islands,” says Asner. 

He also clarifies that with global warming heating oceans around the world, having so many visitors at once is a serious concern for the health of coral reefs, which are known to be very sensitive to changes in temperature.

“The reef becomes stressed as the temperature goes up, and then the effects of people directly on those warming reefs is exacerbated,” says Asner. “It’s like an amplifier. It takes a little bit of heat to stress a reef, and then you put people on it, and the reef goes belly up.”

What are Tourists Doing to Cause the Degradation of Coral Reefs in Hawaii? 

Though there is a strong correlation between overtourism and coral reef degradation, there is still the question of what exactly tourists are doing to cause such harm to coral reefs in Hawaii. 

Asner explains that there are a few reasons tourists are causing coral reef degradation. The first, and most obvious problem being physical contact with the reefs themselves.

As he stated, overtourism has filled certain coastal coral reef locations with more and more people every year. These hotspots become so overcrowded that abrasive contact with the coral reefs is almost guaranteed; and despite their rock-like appearance, they are still very susceptible to direct physical damage. 

Secondly, what Asner is clear to say is only circumstantial evidence, the water at these locations is in many cases polluted with not only debris and garbage, but also the urine of the tourists who swim there. An individual’s urine can contain all kinds of unwanted and harmful chemicals, the kind that can cause serious harm to coral. Ibuprofen, and even caffeine can be very detrimental to the health of a living coral reef, especially if exposure occurs on a daily basis.  

However, as Asner further elaborates, it is not only the chemicals tourists put into their bodies that are causing harm, it’s also the chemicals that they are putting on to their bodies. In a separate study published by Environmental Health Perspectives, it was found that the chemicals in sunscreen can cause “abrupt and complete bleaching of hard corals,” even at extremely low concentrations. Rather disturbingly, the researchers found that the chemicals – paraben, cinnamate, benzophenone, and camphor derivatives – stimulated dormant viral infections in their zooxanthellae (the symbiotic algal component of coral) subjects, which in turn, caused them to explode. This explosion then spread viruses outwards into the surrounding seawater, which resulted in further infections to nearby coral communities. 

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Residential Effluent a Serious Concern for Coral Reef Health

Although overtourism has proven to be unsustainable for natural ecosystems like coral reefs, it is not the sole reason for coral reef degradation in Hawaii. There is another, less obvious reason; one that many may not even be aware of.

“It’s really well known here, but I think the rest of the world doesn’t know about it,” says Asner. “We have 88,000 cesspools – just holes in the ground – that human waste and laundry detergent goes into.”

According to Asner, the government of Hawaii attempted to circumnavigate this issue by developing septic tank infrastructure, however the tanks still require leach fields, which only capture the toilet paper and other solids, while expelling the liquids regardless. 

Furthermore, because younger islands like the Big Island (as it’s known by locals) are mainly composed of basalt, there is less soil available in comparison to the older islands. This means that the liquids expelled by both septic-tank leach fields and cesspools have nowhere to go but back out into the ocean. In a study published by the Journal of Hydrology: Regional Studies, researchers from the University of Hawaii at Hilo used dyes to follow how far the effluent from septic tanks, otherwise known as onsite sewage disposal systems, traveled. Their findings suggest that the effluent from these tanks is quite capable of reaching shorelines, thereby polluting coastal waters. 

“Scientists have very clearly shown that both are equally a problem, septic tanks and cesspools,” explains Asner. 

What Can Be Done to Prevent Coral Reef Degradation in Hawaii? 

In regards to overtourism, Asner explains that there are two ways that tourists can help mitigate and possibly even prevent damages to coral reefs on their trips to Hawaii. 

“One, educate yourself about these problems, and become part of the story of addressing them. We want people to come here, but we want them to come here really educated. And not social media educated, but really educated about what the situation is,” says Asner.

He explains that every swimmer visiting Hawaii’s coastlines should be wearing rash guards and, contrary to what your mother may tell you, absolutely no sunscreen. He also recommends that people stay as far from the coral reefs as possible, at least a 20-foot distance. 

The second method of damage mitigation, as Asner states frankly, is to use the washrooms on the mainland, rather than the ocean as a toilet. 

“At least it’s not right on the reef. You know?” he says.

As for residential waste, Asner believes that the focus should be on upgrading and streamlining their wastewater-treatment infrastructure, a task that not only involves the government, but the people of Hawaii. “We have got to work together to get our wastewater treatment fixed. The county and state want to do it, but they need communities to want to as well.” 

He explains that although there is money available to implement more refined and modern wastewater-treatment infrastructure, many residents of Hawaii are unwilling to go through the process of installation; a process that entails extensive excavation, construction and manipulation of their yards and homes.

“A lot of people are just not lifting a finger about it. And there isn’t enough federal regulation to force it fast enough. So it’s really a collaborative process where there is money to do these wastewater treatment facilities, but people are going to have to dig up a small part of their yards,” says Asner.

Help is Needed to Save Coral Reefs in Hawaii

Currently, Asner and his colleagues are building the largest coral reef restoration facility in the Pacific, a venture that will require as many hands on deck as possible. In light of this fact, Asner is asking anyone, especially tourists and the residents of Hawaii, to help out by cleaning the land, particularly where coral reefs are most prominent.

“We need people to clean up the land,” says Asner. “If we restore coral reefs in areas where land is still being polluted, the reef will just die again.”

In addition, they’ll eventually need help collecting what are known as COO’s, or “corals of opportunity,” which are essentially coral that have been separated from their communities due to storms, ship-groundings, anchors, and other mishaps. By June of this year, their restoration facility will be fully functional, allowing for the storing of half a million COO’s within coral nurseries, for the purpose of not only rehabilitation, but propagation.   

“We can take one coral, and we can create 10 or 20 out of that same coral. They’re called clones–coral clones.” explains Asner. “We can take those corals into the nursery, propagate them, and then we can go out and plant them back on the reef.”

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