Hanauma Bay Nature Preserve, a renowned snorkeling destination in Hawai’i, witnessed a significant ecological revival during the 2020 pandemic lockdowns. With nearly a million visitors annually, the bay experienced a rare period of human absence, leading to clearer waters and a resurgence of marine life. A study by the Hawaiʻi Institute of Marine Biology (HIMB), published in npj Ocean Sustainability, highlights these changes, noting increased sightings of endangered Hawaiian monk seals and more active fish populations.
“We took advantage of a unique ‘natural experiment’ created by the COVID-19 pandemic,” explained Aviv Suan, Project Manager in HIMB’s Elizabeth Madin Lab. “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.”
Ecological Insights from the Pandemic
The study’s findings reveal that the absence of human visitors allowed the reef to return to more natural conditions. Fish densities shifted, and vital herbivores like parrotfish became more active in grazing algae. This rapid response underscores the sensitivity of coral reefs to human presence.
“The ecosystem responded in remarkable ways,” shared Dr. Elizabeth Main, lead author 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 Recovery
The findings from Hanauma Bay provide a compelling message: coral reef ecosystems possess remarkable resilience, and key components can recover swiftly when human pressures are reduced. “Hanauma Bay is one of the most iconic marine ecosystems in the state,” emphasized 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 research serves as a valuable case study for marine managers globally, offering a science-based roadmap for sustainable tourism and conservation strategies that benefit both the environment and the economy.
Implications for Future Tourism and Conservation
The study suggests that implementing visitor caps on reefs, particularly those currently unregulated, could restore ecological functions and alleviate human pressures while maintaining access. “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,” explains Madin.
The Hanauma Bay study not only highlights the potential for rapid ecological recovery but also underscores the importance of sustainable management practices. As tourism resumes, these insights could guide policies that balance environmental health with economic interests, ensuring the long-term vitality of both the reefs and the communities that rely on them.
Reference: Madin EMP, Suan A, Severino SJL, et al. COVID-19 anthropause affects coral reef ecosystems through biophysical changes. npj Ocean Sustain. 2025. doi:10.1038/s44183-025-00144-3
