New study reveals tourists love Hawaiian coral reefs just a little too much

Researchers combine social media with aerial mapping of sea floor to find tourism negatively impacts coral reefs

January 9, 2023

Coral reefs are vibrant ecosystems for marine life and provide vital environmental benefits for humanity, such as storm wave mitigation, bountiful fish stocks and ocean-based livelihoods. They are also a global attraction for tourists, drawing millions of visitors every year and billions of dollars in tourism revenue.

However, reef ecosystems are also as fragile as they are beautiful. Coral reefs are swiftly and steadily declining due to the combined effects of global warming and local human stressors. A new study by Arizona State University and Princeton University provides insights into the local impacts of tourist visitation on live coral cover, as well as the draw reefs can have for coastal visitation. Tourists fill a Hawaiian beach. Hawaiian coral reefs are popular tourist sites. This is cause for concern, as highly visited coral reefs are negatively impacted by elevated pollution, infrastructure and development, as well as on-reef visitation and the physical damages accrued through recreating tourists. Photo by Greg Asner Download Full Image

The study, published Jan. 9 in the journal Nature Sustainability, provides novel evidence that live coral reef cover is both an attraction for and victim of tourists at a large scale, raising complex trade-offs between environment and the economy.

Even though tourism revenue is a boon to the economy and can benefit reef preservation efforts, when unmanaged, increased tourism also negatively impacts the health of coral reefs directly, both through tourism-related development and pollution, as well as on-reef activities such as swimming, scuba diving and snorkeling.

“We took the world's first live coral maps and combined them with the power of social media and data analytics to derive wholly new information on the interaction between people and reefs,” said Greg Asner, co-author on the study and director of the ASU Center for Global Discovery and Conservation Science in the Julie Ann Wrigley Global Futures Laboratory.

“The results were astonishing to see at such a large geographic scale and yet also corroborative at the local scales in which some communities have voiced significant concern about coral reef tourism,” Asner said.

Coastal tourism is a multibillion-dollar industry and will increasingly feature in the future use of marine resources,” said Bing Lin, a doctoral student at Princeton University’s School of Public and International Affairs and lead author of the study. “It is only through an adequate understanding of tourism’s large-scale impacts on reef ecosystems that we can appropriately pinpoint pathways to make it more sustainable."

The research team created unique, high-resolution datasets collected at the archipelago scale across the state of Hawaii, a prime coastal tourism hotspot. To determine coastal visitation rates, Lin web-scraped hundreds of thousands of Instagram posts to quantify both on-reef and overall coastal visitation. To quantify live coral cover, the authors used a high-resolution airborne mapping and a machine learning procedure to map the seafloor, a method developed by Asner and colleagues. Lin then obtained additional information from the Ocean Tipping Points project and the Hawaii Statewide GIS Program on various metrics of site accessibility, human activity and water conditions to determine the relationship between tourist visitation and live coral cover across hundreds of coastal sites in Hawaii.

Plane flying over a coastline.

ASU researchers used high-resolution airborne mapping and a machine learning procedure to map the Hawaiian sea floor. This image shows the ASU Global Airborne Observatory in action. Photo by ASU

They found that high-quality coral reefs are popular tourist sites for both overall and on-reef specific visitation. At the most highly visited sites, coral reefs were also doubly at risk from tourism. They are indirectly impacted by the elevated pollution and infrastructure development it brings and directly impacted by on-reef visitation and the physical damages accrued through recreating tourists.

These findings provide new insights into the role of local human activities in impacting coral reef health, a finding only possible through the high-resolution, meter-scale mapping methods used in this study.

“Whether it's through our airborne program in regions like Hawaii or via our global reef monitoring program, we are constantly reminded that negative local-scale impacts are outpacing climate change-related impacts on coral reefs,” Asner said. 

“Local stressors to the world’s reefs are often overshadowed by the large, looming threat of global climate change and subsequent coral bleaching. However, our research underscores the importance of localized stressors in also contributing to coral decline,” Lin said.

This study also highlights the importance of both strong reef-protecting policies and coral restoration measures, especially at popular tourist sites across Hawaii and beyond. Higher rates of on-reef visitation occur when there is better reef quality, site accessibility and water quality. This suggests that potential synergies also exist in promoting stronger coastal management practices that can simultaneously improve both reef quality and revenues generated from tourism.

This study was supported through funding from the High Meadows Foundation and the Lenfest Ocean Program of The Pew Charitable Trusts.

Keely Swan with Princeton University contributed to this article.

Sandra Leander

Assistant Director of Media Relations, ASU Knowledge Enterprise


Study of California groundwater prompts a wake-up call for Arizona

Lessons learned from satellite data show urgent need to stabilize underground aquifers

January 9, 2023

A team of scientists that pioneered methods to observe changes in global groundwater stores over the past two decades using a specialized NASA satellite mission has made a surprising discovery about the aquifers that supply California’s Central Valley region.

Despite the Sustainable Groundwater Management Act adopted in 2014 to prevent overpumping and stabilize the aquifers, the groundwater depletion rate has accelerated to a point where groundwater could disappear over the next several decades. The act gives the state’s local groundwater management districts until 2042 to reach sustainability goals. NASA/German Research Centre for Geosciences rocket launches into the sky. Researchers used data from a special NASA satellite to discover changes in groundwater stores. In this image, the NASA/German Research Centre for Geosciences GRACE Follow-On spacecraft launched onboard a SpaceX Falcon 9 rocket on May 22, 2018, from Vandenberg Air Force Base in California. This mission measured changes in how mass is redistributed within and among Earth's atmosphere, oceans, land and ice sheets, as well as within Earth itself. Photo courtesy NASA/Bill Ingalls Download Full Image

Renowned water scientist Jay Famiglietti is the lead researcher of a scientific team that published a paper in Nature Communications in December 2022 that details their analysis.

Famiglietti has a blunt message: “All around the world, we have been kicking the can down the road for a long time on effectively managing groundwater. Now we are at the end of the road, and it’s a dead end." Famiglietti is a professor with the Arizona State University School of Sustainability in the College of Global Futures, a unit of the Julie Ann Wrigley Global Futures Laboratory.

Famiglietti joined ASU in January to assist in developing the new Arizona Water Innovation Initiative, established through a $40 million investment by the state of Arizona.

Among the world’s most productive agricultural areas, California’s Central Valley grows most of the produce consumed across North America. To do that, it relies heavily on aquifers — as much as 100% during droughts. While groundwater has been disappearing from the region for almost a century, the increasing rate of drawdown in recent years is completely unsustainable, Famiglietti said.

“If that water disappears, so does food production. That means less produce, higher prices, shortages and other shocks to food systems,” said Famiglietti, previously the Canada 150 Research Chair in Hydrology and Remote Sensing at the University of Saskatchewan and executive director of USask’s Global Institute for Water Security.

“My fear is that if we wait 20 years to bring these aquifers to sustainability, there may not be anything left,” he said. “Speeding up the implementation period may be worth considering, because there appears to be a rush to pump as much as possible before the hammer comes down.”

Portrait of .

ASU Professor Jay Famiglietti

His team analyzed nearly two decades of data collected by NASA’s Gravity Recovery and Climate Experiment satellite and the GRACE Follow-On satellite. Their research shows groundwater losses during 2019 to 2021 — the driest three-year period in California’s history — were 31% faster than in two previous drought periods of 2006 to 2011 and 2011 to 2017. This rate is also nearly five times greater than the long-term average rate of depletion since 1962.

Deep groundwater took millions of years to accumulate, Famiglietti said, and the current scale and pace of the depletion means that recharging the supply is virtually impossible.

“We talk about managed aquifer recharge and replenishing some of these aquifers. But that’s a small amount of water, and it’s close to the surface. This is industrial scale mining of groundwater, with virtually no chance on human time scales to replace the losses.”

The impacts of depletion extend far beyond food production, he said. A big issue is the subsidence, or sinking of the ground, which can potentially affect about one-quarter of the Central Valley.

Water for desert cities, including in major U.S. cities such as Phoenix, Las Vegas, Tucson, Arizona, and Salt Lake City, will be also scarcer, he said.

As groundwater disappears, there is ecological damage as wetlands are drained and streams run dry. And as water tables fall, costs increase to dig deeper wells and pump groundwater higher, creating affordability problems for people who need to access the water. Additionally, the poorer quality of deep water makes its treatment expensive.

Graph illustrating groundwater depletion.

Groundwater losses combining the USGS’s Central Valley Hydrologic Model and the GRACE/FO estimates since 1962. The black line represents the overall groundwater depletion from 1962 to 2021, calculated by combining the CVHM and GRACE estimates.

What’s happening in the Central Valley is also happening in the Lower Colorado Basin, the southern part of the High Plains Ogallala Aquifer, the Middle East, India and Bangladesh, and several other major food-producing regions around the world, he said.

This depletion of groundwater should be a wake-up call for Arizona, where groundwater constitutes 40% of the state’s water supply and contributes 43% to its GDP.  Yet, outside of the state’s 5 Active Management Areas, groundwater is largely unregulated.

“Arizona is at a crossroads with its groundwater use,” said Famiglietti. “The management decisions it makes today, including how to allocate groundwater for cities, agriculture, industry and the environment, will largely determine its vitality over the next century.

“An important first step will be to carefully measure how much groundwater we actually have in Arizona and how much we are using, so that we can balance that with declining surface water availability from the Colorado River. We need to be able to support innovation and food production, but we need to do it for centuries, not just for a few decades.”

Sarath Peiris with the University of Sasketchewan contributed to this article.

Sandra Leander

Assistant Director of Media Relations, ASU Knowledge Enterprise