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Lack Of Visitors Offers Opportunity To Explore Human Impact On Marine Ecosystems

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Hanauma Bay, located on the southeast corner of Oahu, is one of the state's most popular attractions.

The drastic reduction in visitors coming to Hawaii has afforded scientists a unique opportunity to see how one of the state’s most popular natural attractions fares without a human presence.

Roughly 3,000 people per day were visiting the blue water and white sand of Hanauma Bay  prior to the pandemic. Those 1 million annual visitors carry a major environmental footprint.

The crescent-shaped inlet on Oahu’s southeast corner has been used as an example of both over-tourism and sustainably-managed tourism over the years. It was declared a marine conservation area in the 1960s, after decades of degradation from over use. In an effort to help fund maintenance and reduce impact, visitors are now charged an entry fee and public parking is limited.

However, that has drastically changed in the age of COVID-19. The number of visitors coming to Hawaii is down by more than 90% from previous levels, according to monthly data from the Hawaii Tourism Authority.

Marine scientists are using that lull to study how the presence of humans, or lack thereof, impacts the ecosystem Hauanuma Bay. No one has been allowed into Hanauma since the start of the pandemic in March, when Gov. David Ige ordered the nature preserve closed due to concerns over the large crowd that normally gathers there.

That has presented Elizabeth Madin, a marine scientist at the Hawaii Institute of Marine Biology, the opportunity for what scientist call a “natural experiment.”

“This is an amazing opportunity scientifically to see what happens to reef and other  marine ecosystems and terrestrial ecosystems when humans basically stop doing what they do in those ecosystems,” Madin said in an interview.

Madin’s colleagues at the University of Hawaii’s Coral Reef Ecology lab have already been monitoring the health of the Hanauma Bay ecosystem for two decades, with a particular focus on the bay’s coral reefs. That work has helped make the case for conservation efforts currently in place at Hanauma, including a requirement that all visitors watch an informational video depicting the dos and don’ts of interacting with corals and other wildlife.

However, until now, scientists have never had a chance to see how the Hanauma Bay ecosystem functions without a significant presence of people.

Madin will specifically be looking at fish behavior. Using a network of GoPro cameras (what they refer to as a “camera trap”), her team will record hours upon hours of fish behavior at sites throughout the bay. This is meant to establish a baseline for natural fish behavior, without the influence of humans.

“We would expect that they’ll revert to more natural levels of things like feeding, so eating algae, and predator-prey interactions,” Madin hypothesized.

“And conversely, that those behaviors would be re-altered once visitors to the bay return post-COVID.”

Whenever people do return to Hanauma, scientists will be able to observe how fish change their behavior in the presence of humans, thereby giving them a fuller understanding of the human impact on the marine ecosystem.

That will have potentially significant implications for future conservation efforts. As a hypothetical, Madin suggests an outcome where a human presence is found to decrease the feeding activity of herbivorous fish that eat the algae growing on coral reefs.

“This would then suggest that human presence indirectly restricts plant-eating fishes from performing one of their key ecological functions -- keeping the reef’s algae in check and providing space for new corals to grow,” Madin explains.

Studies in other areas have shown that some fish do adapt their behavior in the presence of humans. In areas frequented by spear fisherman, fish have been observed to be more wary of humans in the water, the technical measure of which is known as the “flight initiation distance.”

But that is not necessarily the case in Haunama Bay. The area is legally designated as a marine conservation preserve, meaning humans are not allowed to fish there, even for catch and release.  

Madin says that it is possible the legally-protected fish living in Hanauma Bay have adapted over generations and no longer see humans as a threat.  If that turns out to be the case, fish in the bay may not be altering their natural behavior, despite a large presence of people.

Regardless of their outcome, the results will provide scientists and policy makers valuable insight on both the direct and indirect impact human beings have on Haunama Bay. That in turn will allow conservation managers to more accurately determine how much human activity the bay’s ecosystem can support.

“At what level can we have visitors come and swim on the reef without having a negative impact on the way the reef functions,” Madin says, summarizing one of the hoped for insights of the study.

Coral reefs contribute more than $3 billion worth of economic value to Hawaii annually, according the Coral Reef Education Institute and Hawaii Department of Land and Natural Resources. That does not cover the additional environmental value reefs provide by protecting infrastructure from damage and sustaining marine ecosystems.

Studies like this one will help planners figure out how to keep already threatened reefs open for eco-tourism without permanently degrading them, or as Madin puts it, “over loving” them.

A timeline for reaching such a conclusion remains undetermined. Researchers will need several months of consistent human activity in the bay before that assessment can be made.

With cases of COVID-19 still  widespread on multiple islands, such a scenario is unlikely before 2021.

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