Hawaii is amongst the most vulnerable areas to the climate crisis: the ocean is warming, coastal erosion is accelerating, marine ecosystems are weakening. Yet along the coast of Molokaʻi Island, there is an exception. In some coastal basins, the water remains cooler than the open sea, even in the hottest months.
These are loko iʻa, traditional aquaculture systems built by Native Hawaiian communities more than 800 years ago. According to a study published in npj Ocean Sustainability, these structures offer surprising thermal stability and could become a model for local climate adaptation.
The team, led by Annie Innes-Gold, a researcher at the Mānoa Institute of Marine Biology, built a simulation model to understand how these ancient systems will respond to global warming, revealing that indigenous aquaculture systems effectively protect fish populations from the negative impacts of climate change, demonstrating resilience and enhancing local food security. The secret lies in their structure. Fresh water from underground streams and springs continuously mixes with marine water, creating a natural cooling effect. Whilst average temperatures in the bay rise steadily, the ponds maintain fluctuations approaching 25 °C, the optimal temperature for the iconic species in these systems.
Three strategies to be integrated
Simulations projected to 2100 show that, without intervention, fish populations in the ponds will endure better than those in the surrounding bay. But the benefits increase if three strategies are integrated: watershed restoration to increase nutrients and water flow, controlled release of young fish from hatcheries, and regulation of fishing. Under these “combined” scenarios, fish densities can nearly double from current conditions. The study is the first to provide detailed quantitative data on their climate resilience.
“These results highlight the importance of freshwater input as a source of temperature regulation,” explains Innes-Gold, first author of the research. “They also support the value of biocultural restoration: not only for increasing fish populations, but for building social-ecological resilience in a changing climate.”
Loko iʻa are monumental aquaculture systems that Hawaiians have built along the coasts for centuries. Aquatic basins that could extend from less than a hectare to hundreds of acres, separated from the sea by stone walls and equipped with sophisticated sluice gates that regulated water flows. The cardinal principle is to retain nutrient-rich waters long enough to multiply fish productivity over natural estuaries.
Decimated in the 20th century
In the precolonial period, the archipelago had 500 of them. But the 20th century, amid urbanisation, colonisation and natural disasters, reduced their operation, and by the end of the 20th century only six remained. In recent decades, however, a biocultural restoration movement has begun: a holistic approach that integrates ecosystem rehabilitation with cultural revitalisation and strengthening ties between communities and places. Today some fifty loko iʻa are active or undergoing restoration, often through collaboration between native communities, research centres and public institutions.
“Loko iʻa are a unique system,” Innes-Gold concludes. “Their restoration can generate far-reaching benefits: cultural conservation, education, healthy ecosystems, food security and, as we found in this study, even climate resilience.”
The researchers point out that these structures are complex ecological and cultural systems that integrate resource management, collective practices and ecological knowledge passed down through the centuries. Their value also lies in their inherent sustainability: no mechanical equipment, no external energy demands, but an ecological design that has remained functional for centuries. And the model could set a school, inspiring adaptation strategies for other indigenous aquaculture systems in the Pacific and beyond, from the clam gardens of British Columbia to the fish ponds of Indonesia, China and Europe.
