Although it’s a lot quieter, some things have been getting livelier at Hanauma Bay Nature Preserve since it was closed to human visitors March 18 due to the novel coronavirus pandemic.

“We’ve been seeing more of the larger omelu and ulua (trevally jacks) coming in very close to shore — really big guys who just seem to be checking you out,” said Sarah Severino, one of the scientists with the Coral Reef Ecology Lab of the University of Hawaii at Manoa Institute for Marine Biology. The institute has been conducting research on water quality, coral health and fish behavior in the bay on behalf of the City of Honolulu Department of Parks and Recreation before and during the closure.

“Oh my gosh,” Severino added with a laugh, “these guys just sneak up on you and then flash past you — you hardly ever see anything that big in the bay except a monk seal.”

The scientists also have been seeing increased monk seal activity, both in the water and basking on the sands, but these sightings, along with those of the big bluewater predators, are “only anecdotal at this point, because we haven’t had time to work up that data yet,” Severino said. For the past five months, a small, socially distancing institute team has been collecting data in the waters and along the shorelines on Tuesdays, formerly the one day of the week that the bay was closed to the public.

Overall, however, the institute’s recently published new research indicates the Hanauma Bay Nature Preserve ecosystem has been growing healthier since it’s been closed to visitors, DPR announced in a press release Friday, citing the findings of the “Hanauma Bay Biological Carrying Capacity Survey 2019 -2020 2nd Annual Report,” co-authored by Severino, principal investigator Kuulei Rogers, Yuko Stender and Mathew Stefanak. The report was published this month on DPR’s website.

“Of the many unforeseen circumstances presented by the COVID-19 pandemic, the reduced human presence at locations around our islands has presented a unique opportunity to better understand and manage our impacts on the natural environment,” DPR said in the release. “Of those locations, the Hanauma Bay Nature Preserve is arguably the most prominent,” it added, noting that the bay normally received an average of nearly 3,000 people every day, except for Tuesdays, Christmas and New Year’s Day, when it was closed.

Perhaps most striking to date has been the quantifiable improvement in water clarity: The bay’s water is 18% clearer, with improved visibility of 2 meters, than when the scientists tested it during regular Tuesday closures of the bay before the comprehensive pandemic closure, and 42% clearer, with improved visibility of 4.9 meters, than it was on days when the bay was open to the public.

The water clarity data, collected through June, was compared with data recorded in 2018 for the first biological carrying capacity study conducted by the Coral Reef Ecology Lab.

The survey also provides information comparing the impacts of coral bleaching events in 2015 and 2019, monitors the biodiversity and characteristics of the bay’s marine life, and will eventually determine “acceptable limits of human disturbance with this unique ecosystem,” DPR said.

The determination of carrying capacity, in terms of visitors, will depend upon continuing research observing what happens in the bay after humans return, Severino said.

Sediment traps placed on the reef will be used to see if there is more sedimentation after tourists come back.

In terms of fish behavior, the team has shot videos of herbivorous fish foraging the reef and how close fish let swimming scientists approach before they turn away and flee.

“Once it opens back up to the public, we’ll be able to tell if their flee time or feeding behaviors are any different,” she said.

“We’ve looked at the average size of the bay’s coral colony since 2015 and also the number of colonies, and what we’ve noticed is that (after the bleaching event) in 2015 there were less colonies total, but they were larger in area,” Severino said. “Now, there are much more colonies but they’re much smaller in area.”

This means that larger colonies are dying or partially dying, “leaving us with several little colonies,” she said, “and partial mortality could be increased by increase in sedimentation, trampling (by snorkelers) and bleaching events (caused by warming seas due to climate change).

Noting that the scientists saw less mortality (8.23%) in the 2019 bleaching event than in 2015 (10% coral mortality), “we’re trying to identify which of these indicators — corals, fish behaviors, sedimentation of the reef — are a limiting factor (on carrying capacity),” Severino said, “and then we have to determine accessible level of use to minimize damage to whatever that factor is.”

While the greatest threat to the bay is global climate change, she said, “we overall want to mitigate impacts from tourists to make the bay as resilient as possible when these global bleaching events come around.”

In addition to ongoing research of the human impacts on the nature preserve, maintenance and upkeep of the facilities has continued during the closure, including replacing invasive plants with native flora, and bathroom/ sewage system makeovers, DPR said in the release, adding that, currently, there is no set public reopening date for Hanauma Bay.

The report can be viewed at 808ne.ws/31CT7LX.