As sea level rise accelerates around Hawaiʻi Island, anchialine pools along the Kona Coast are changing in ways that worry scientists and cultural practitioners who depend on these unique waters. Anchialine pools, fed by both the ocean and fresh groundwater, are being inundated more often by waves and runoff, even as new pools begin to form inland.
Unlike tide pools, anchialine pools are connected to the sea through underground channels while drawing freshwater from below. They occur statewide, but the Kona Coast holds the vast majority, with more than 400 known sites. Historically, the pools served many purposes. Some were reserved for aliʻi to bathe. Others supplied precious drinking and irrigation water in a dry region and offered fishermen a cool place to hold their catch.
The pools also support rare native species, including ʻōpae ʻula, the tiny red shrimp prized as bait to feed ʻōpelu during spawning, as well as a swimming crab, the orangeblack Hawaiian damselfly and the aeʻo, or Hawaiian stilt.
Today, higher surf is pushing into anchialine pools more frequently, transporting invasive fish that alter the ecosystems. Flooding and intense rain can sweep wastewater toward the coast, adding nitrogen that fuels algal growth.
Awareness remains limited. “There’s a very small sample of folks who are even aware of anchialine pools,” said Barbara Seidel, Hawaiʻi Island marine coordinator for The Nature Conservancy.
Seidel helps lead Hui Loko, a coalition of 23 groups restoring pools along West Hawaiʻi. Volunteers form bucket brigades to clear invasive plants and remove tilapia and other nonnative fish, while working to build broader public support for protecting these cultural and ecological resources.
Mapping and restoring anchialine pools
Many pools were lost during early tourism development along Kona’s shoreline. Hawaiian scholar Hannah Springer noted that while kūpuna relied on the pools for water, habitat and agriculture, later arrivals often failed to recognize their value, and some sites were buried under runways and resorts.
About a decade ago, a coordinated effort ramped up to map remaining pools and plan for climate impacts, led by the National Oceanic and Atmospheric Administration with partners including the National Park Service, the University of Hawaiʻi and The Nature Conservancy.
UH Hilo affiliate faculty member Lisa Marrack developed a sea level rise model for NOAA showing that pool ecosystems face major shifts. Her maps projected that many anchialine pools would expand, merge and, in some cases, transition into saltwater fishponds.
As reef and invasive fish occupy those waters, native shrimp retreat into subsurface cracks and groundwater, emerging at night to graze algae.
Marrack’s work also indicated that new pools would likely appear further inland, providing fresh habitat for shrimp that move between surface and subterranean zones. Seven years on, researchers are documenting those changes and emphasizing the need to protect emerging pools and improve the quality of groundwater flowing through them.
At Kaloko-Honokōhau National Historical Park, less than a mile from the Kealakehe Wastewater Treatment Plant where minimally treated R2 effluent is discharged into a lava field, Marrack and colleagues examined ʻōpae ʻula and found the shrimp are effective bioindicators of sewage in groundwater at coastal habitats.
Where invasive fish are absent, the shrimp can keep algae in check. The research cautioned that rising groundwater will increase contact between coastal aquifers and sewage infrastructure, potentially heightening contamination.
Protecting future anchialine pools
Kevin Sullivan, a planner with Hawaiʻi County’s Long Range Division, described anchialine pools as “visible expressions of a larger underground groundwater system connecting upland recharge, coastal aquifers, wetlands and the ocean.” He cited the county’s Integrated Wastewater Management Plan and a One Water approach that manages drinking water, wastewater and stormwater as a single resource to improve coastal water quality.
Hawaiʻi County’s General Plan 2045 calls for development that avoids harming anchialine pools and estuaries, and for a program to acquire and restore pools through collaborative biocultural stewardship. Turning that intent into action will require follow-up legislation.
“Future anchialine habitat may presently look like undeveloped dry land,” Sullivan said. “Once that land is developed, filled or covered with permanent infrastructure, the opportunity for the ecosystem to migrate inland in response to rising groundwater may be permanently lost.”
In the remote Kamilo area of Kaʻū, aquatic biologist Troy Sakihara of the DLNR Division of Aquatic Resources surveyed several pools between 2008 and 2010. “Within the past several years, we’ve seen a lot of those become tide pools,” he said. New pools have already appeared in neighboring Manukā Natural Area Reserve.
Sakihara works with Marrack, using her maps to anticipate where pools may emerge. Clearing invasive vegetation and species in advance, he said, can give new pools a healthier start.
While the county’s plan does not set explicit buffer zones for new pools, Sakihara said he supports clear directives to limit development impacts. He has collaborated with Hawaiʻi Wildlife Fund and other Hui Loko members on a proposed resolution to reduce human-caused harm, including stopping tilapia introductions and curbing the harvest of shrimp for aquariums.
The measure would need to move through the DLNR rulemaking process before any statewide policies take effect. Advocates also backed a successful bill naming ʻōpae ʻula Hawaiʻi’s official state shrimp in 2025, aiming to raise awareness and strengthen protection efforts.
Hui Loko members continue to gather quarterly to share strategies and restore sites. Seidel said the group functions like a support network for the small community that cares for the often-overlooked ponds.
The work can be grueling, but results arrive quickly when invasive fish are removed. She recalled a 2020 restoration where a pool, once cleared, teemed again with native shrimp the following week.
The ʻōpae ʻula, she said, had been waiting in the cracks all along.
Related efforts to preserve climate data, such as the Climate.us relaunch, underscore the importance of long-term information for protecting sensitive ecosystems like anchialine pools.
