Hanauma Bay Nature Preserve, a renowned snorkeling destination in Hawai’i, experienced a swift ecological revival during the 2020 pandemic lockdowns. The bay, which typically welcomes nearly a million tourists annually, saw significant environmental improvements when tourism halted. A recent study by the Hawaiʻi Institute of Marine Biology (HIMB), published in the journal npj Ocean Sustainability, highlights clearer waters, increased sightings of endangered Hawaiian monk seals, and more vibrant fish populations during this period.
“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. The lab focuses on the impacts of human activity on marine ecosystems through advanced research techniques. Suan noted, “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.”
Environmental Recovery During Human Absence
By assessing the physical and biological health of the ecosystem, researchers discovered that the reef in Hanauma Bay quickly reverted to more natural conditions when humans were absent. Fish densities shifted, and essential herbivores like parrotfish became more active in grazing algae.
Dr. Elizabeth Main, lead author of the study and principal investigator of the Elizabeth Madin Lab, shared, “The ecosystem responded in remarkable ways. 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 of Coral Reefs
The findings underscore the resilience of coral reef ecosystems, demonstrating that certain key elements can recover rapidly when human pressures are alleviated.
“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 can benefit both the environment and the economy.
Implications for Sustainable Tourism
“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.”
“COVID-19 anthropause affects coral reef ecosystems through biophysical changes.” – Madin EMP, Suan A, Severino SJL, et al. npj Ocean Sustain. 2025. doi:10.1038/s44183-025-00144-3
The study’s implications extend beyond Hawai‘i, offering insights into how temporary reductions in human activity can lead to significant ecological benefits. As the world seeks to balance economic interests with environmental sustainability, Hanauma Bay’s experience provides a compelling example of the potential for positive change.
