In 2020, Human Absence Led to a Nature Revival in Hawaii

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Hanauma Bay Nature Preserve, a well-liked Hawai’i snorkeling vacation spot that pulls almost 1,000,000 annual guests, underwent a outstanding and fast restoration when tourism ceased throughout the 2020 pandemic. A brand new research from the Hawaiʻi Institute of Marine Biology (HIMB), printed final week within the journal npj Ocean Sustainability, discovered that this era of human absence led to clearer water, elevated sightings of endangered Hawaiian monk seals, and extra lively fish populations.

“We took advantage of a unique ‘natural experiment’ created by the COVID-19 pandemic,” defined Aviv Suan, Project Manager in HIMB’s Elizabeth Madin Lab, which leverages cutting-edge know-how to analysis human impacts on marine ecosystems. “Hanauma Bay is normally a heavily visited site, but was completely closed to the public for seven months. We collected data on water quality, monk seal sightings, fish abundance, and fish behavior before, during, and after the closure. This allowed us to directly compare how the reef responded to different levels of human activity.”

By measuring the bodily and organic well being of the ecosystem, the analysis crew discovered that when human guests had been absent, the reef in Hanauma Bay rapidly returned to extra pure ranges. Fish densities modified and very important herbivores like parrotfish grew to become extra lively in grazing algae. 

“The ecosystem responded in remarkable ways,” shared Dr. Elizabeth Main, lead creator of the research and principal investigator of the Elizabeth Madin Lab. “The water became noticeably clearer, endangered Hawaiian monk seals started showing up more often, and fish numbers increased. These kinds of changes happened quickly, suggesting that everyday human presence can have a real and measurable impact on reef health. It’s a powerful reminder of just how sensitive and responsive coral reef ecosystems are to our activity.”

Resilience and restoration

The crew’s findings present a transparent and highly effective message: coral reef ecosystems are extremely resilient, and not less than some key components of the ecosystem can start to get well rapidly when human pressures are lowered.

“Hanauma Bay is one of the most iconic marine ecosystems in the state,” emphasised Suan. “By observing what happened when people were absent, we saw nearly immediate benefits for key parts of the ecosystem. This study is an example of how research at the University of Hawai‘i can directly serve the people of Hawai‘i by helping to guide reef management, protect natural resources, and support a more sustainable future for both ecosystems and local communities.”

This analysis serves as a helpful case research for marine managers not simply in Hawaiʻi, however all over the world, and offers a science-based roadmap for sustainable tourism and efficient conservation methods that may profit each the surroundings and the financial system.

“Putting caps on the number of visitors to reefs—especially those that are currently unregulated—could help restore lost ecological function and ease human pressures while still maintaining access,” explains Madin. “Protecting these ecosystems doesn’t have to come at the cost of the economy. Yes, reef tourism brings in billions of dollars each year, both globally and here in Hawai‘i. In fact, research shows that many visitors are willing to pay more to experience healthier, more vibrant reefs. That means we can potentially reduce crowding and still support the tourism industry and everyone who depends on it—if we manage it wisely.”

Reference: Madin EMP, Suan A, Severino SJL, et al. COVID-19 anthropause impacts coral reef ecosystems via biophysical adjustments. npj Ocean Sustain. 2025. doi:10.1038/s44183-025-00144-3

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