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Hanauma Bay recovering since COVID-19 closure, new research shows

  • Video by Craig T. Kojima and courtesy video by Sarah Serevino

    Hanauma Bay has been closed to the public since March 16 due to the coronavirus pandemic.

  • CRAIG T. KOJIMA / MAY 28
                                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.

    CRAIG T. KOJIMA / MAY 28

    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.

New research indicates the ecosystem of the Hanauma Bay Nature Preserve ecosystem has been growing healthier since it was closed to visitors March 18 due to the novel coronavirus pandemic, the City and County of Honolulu Department of Parks and Recreation announced today.

”Instead of human footprints, researchers have noticed larger fish and the continued increase in monk seal activity within clearer ocean waters of the Nature Preserve,” DPR said in a press release, citing the findings of the “Hanauma Bay Biological Carrying Capacity Survey 2019 -2020 2nd Annual Report” by scientists from the Coral Reef Ecology Lab of the University of Hawai‘i at Manoa Institute for Marine Biology.

Perhaps most striking to date has been the 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 was compared with data recorded in 2018 for the first biological carrying capacity study.

The survey also provides information comparing the impacts of coral bleaching events in 2015 and 2019, monitoring the biodiversity and characteristics of the bay’s marine life, and eventually determining acceptable limits of human disturbance with this unique ecosystem.

The determination of carrying capacity, in terms of visitors, which had averaged 3,000 per day before the closure, will depend upon research looking at what happens in the bay after humans return, said Sarah Severino, coauthor of the survey.

“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 in 2015 there were less colonies total but they were larger in area,” Severino said, “and 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 added, “and partial mortality could be increased by increase in sedimentation, trampling (vy visitors) and bleaching events.”

The increased activity of monk seals and sighting of larger fish, notably omelu and ulua, coming into shallow waters than before the closure, is only anecdotal at this point “because we haven’t had time to work up that data yet,” Severino said; for the past five months, the institute team has been continuing to conduct their research the closed bay on Tuesdays, as it did before the closure.

The survey, which concluded in May 2020, was published this month on DPR’s website.

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.

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