Researchers are taking advantage of an unprecedented absence of visitors to Hanauma Bay Nature Preserve to study the impact of humans on the county park’s diverse marine life, such as coral reefs and the hundreds of species of fluorescent-colored fish that depend on them.

They’ve already seen signs of fish coming out of hiding and they anticipate the bay’s vacation from vacationers will bring a much-needed boost to its overall health.

Honolulu Mayor Kirk Caldwell ordered the shutdown of Hanauma Bay on March 16 due to coronavirus concerns and the park will remain closed at least through April 30. Since then the number of daily visitors to Hawaii’s premier snorkeling destination has sunk from 3,000 to virtually none.

“I don’t want to downplay all of the negative effects that are horrible with this COVID-19, but I’ve got to say that I am so excited about the opportunity for there to not be visitors at Hanauma Bay so that we can see if there’s going to be some form of recovery,” said Ku’ulei Rodgers, principal investigator at the Hawaii Institute of Marine Biology’s Coral Reef Ecology Lab.

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Across Hawaii, concerns over the impact of recreational activities such as swimming, diving and snorkeling on fragile marine ecosystems have increased over the decades with the astonishing growth of the state’s tourism industry.

But it’s been difficult to study the relationship between the mobs of people recreating in nearshore waters and the various forms of environmental degradation that scientists are documenting, especially when there are so many other factors at play — rising ocean temperatures, coral bleaching and stormwater runoff, to name a few.

Now that scientists have a rare chance to study changes to the marine environment with zero human impacts — and then again when the park is repopulated by thousands of visitors per day — it will be much easier to draw out a cause and effect, Rodgers said.

“This allows us to separate out all the extraneous factors that occur so we don’t have to guess at the cause of the changes we’re seeing,” Rodgers said.

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Previous research at Hanauma Bay suggests that human disturbance contributes to coral breakage, as well as the loss of entire coral colonies.

Rodgers said she also suspects that recreational activity at the bay impacts fish feeding behaviors.

“If fish behavior is being disrupted because visitors are in the water, then it means that they may not be grazing or hunting as often as they normally would,” Rodgers said. “It’s something that affects the whole ecosystem.”

She and her team of researchers are using a stereoscopic camera to measure how close the parrotfish, wrasse and other fish species are swimming to the scientists when they enter the water. They’ll calculate the distance again when visitors return to the park.

“We are already seeing just anecdotally that the fish are coming a lot closer and they’re not as afraid now that the park is empty,” Rodgers said.

If this proves to be true, it’s an indication that the feeding behavior of the fish is no longer being interrupted by human activity.

“The longer it stays closed, the longer we can track this,” Rodgers said, “And then once it does reopen, if there are some signs of recovery, we can then start to track how quickly things decline again if we do see change.”

A Long History Of Overuse

Overuse has been a problem at Hanauma Bay since at least the mid-1900s, when new restroom facilities and dirt roads leading down to the beach increased accessibility to the east Oahu park that today draws about 850,000 visitors annually.

In 1967, Hanauma Bay became Hawaii’s first Marine Life Conservation District, a designation that enacted a strict ban on fishing and harvesting of marine life. Additional environmental safeguards were put in place in the 1990s when county officials mapped out a plan to educate park visitors about reef conservation and the hundreds of species of fish that thrive in the bay’s clear blue waters.

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In 1999, scientists including Rodgers launched the state’s first coral reef assessment and monitoring program at Hanauma Bay. There are now more than 50 project sites throughout the state where this work is done, allowing scientists to compare how coral health and stability is changing across Hawaii over time.

Rodgers and her team are now in their second year of analyzing the relationship between big crowds and environmental degradation at Hanauma Bay as the threat looms that Hawaii could someday lose its reputation as a premiere visitor destination if its most iconic vistas and experiences are overrun.

Now Hanauma Bay has a daily visitor cap, increased law enforcement and a requirement that first-time visitors watch a 9-minute safety video. Before entering the park, visitors are educated about preservation efforts and instructed to refrain from damaging the delicate natural resources by walking on the reef or harassing marine life.

Entry fees, along with proceeds from parking and snorkel equipment rentals, go into the Hanauma Bay Nature Preserve Fund, which was created in 1996 to provide for the bay’s operation and maintenance, education and orientation programs for visitors and environmental studies of the preserve.

These visitor management strategies have made Hanauma Bay a statewide model for renewed efforts to address over-tourism at other over-capacity attractions, such as Diamond Head State Monument and Kaiwi State Scenic Shoreline on Oahu, Waianapanapa State Park on Maui and Kealakekua Bay State Historical Park on the Big Island.

Management Strategies Not Always Effective

Yet despite Hanauma Bay’s exemplary management efforts, the park’s biodiverse ecosystem is still being damaged by high levels of patronage, Rodgers said.

“At Hanauma Bay, you do see corals but they’re in vertical spaces,” Rodgers said. “They’re not on the horizontal reef flats. They’re in the cracks and crevices and they’re along the walls in places where people can’t actually trample them.”

The corals face multiple threats, large numbers of snorkelers being just one. In 2014, scientists documented a 10% die-off of corals in the bay due to a mass bleaching event.

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Hanauma Bay is closed every Tuesday. But Rodgers said this one-day breather from human activity doesn’t have a measurable effect on reef health.

“It’s great for management,” she said. “When they have no people there, they can clean up the area and they can do some of the maintenance that they can’t do when there’s a lot of people down on the beaches. But for the ecosystem it makes absolutely no difference.”

“Corals are a very slow-growing species so it’s not going to make any difference to a coral if people aren’t there one day of the week,” she added.

Any positive health effects on the reef and fish during the park’s extended shutdown will likely begin to erode and eventually be erased when the marine preserve reopens to the public, Rodgers said.

But the research will be beneficial to scientists who are trying to understand how quickly a reef can deteriorate from human impacts — and how quickly it can recover. It could also influence visitor management policies at beach attractions across Hawaii.

“These are things that will be important to know not just at Hanauma Bay but everywhere in the state,” Rodgers said.

Of course, every coastal habitat will respond differently to threats or, in this case, the temporary absence of one.

When Kauai fishermen reported a resurgence in the numbers of fish swimming in shallow waters off the coast of Haena after a disastrous springtime flood cut off tourism to the area in 2018, Rodgers was one of several marine scientists who donned a mask and snorkel to try to find out if the observations were true.

The hypothesis was that fish were coming in closer to shore because there were far fewer sunscreen-slicked bodies in the water to disturb them. But Rodgers said the scientists did not find a statistically significant difference in the numbers of fish in the water.

At Hanauma Bay, however, the effect of fewer people in the water could yield an entirely different result, Rodgers said.

That’s because Hanauma Bay is an enclosed, shallow reef flat with no access to fishing, whereas Haena borders the open ocean, where there’s a lot more wave energy and currents so strong that locals have dubbed them “the Niihau express.”

Rodgers said the ongoing research at Hanauma Bay will help people understand their impact on the natural world.

“Although it’s heavily used, Hanauma Bay is extremely valuable to the state in terms of the visitor experience that is happening there,” she said. “So it’s a tradeoff at times. But we can find ways to be smarter about it.”