The island of Hawaiʻi is home to a network of unique groundwater-fed anchialine pools, wetlands, and fishponds, which support numerous endemic species as well as provide key ecosystem services to natural and human communities. As sea level rises, these habitats may shift inland if open space is available and conditions are suitable. These shifts may benefit ecosystem integrity due to habitat expansion, or impair it by changing hydrology or facilitating the spread of invasive species. Ideally, potential habitat sites can be protected and incorporated into restoration efforts so that vulnerable ecosystems and species will persist into the future and long-term integrity of conservation and restoration efforts can be supported. Predicting the effect of sea-level rise on these ecosystems requires models that incorporate groundwater levels which are elevated above sea levels and will exacerbate flooding in the porous basalt aquifer.
As the only island state in the US, Hawaiʻi’s people have a profound connection with the ocean. Communities thrive at the interface of land and sea. As our climate changes, higher sea level and increased storm frequency and intensity can have unprecedented impacts on the people, infrastructure, and ecology of this unique place. Coral reefs, intertidal zones, anchialine pools and fishpond habitats may shift inland in low-lying areas. People, infrastructure, and nature have the potential to collide to a degree previously unseen. Reefs may face pollutants from degraded coastal infrastructure, and inland groundwater pools may connect in ways that facilitate the spread of invasive species. Completely new anchialine pool habitats may be created as sea level rises through the porous basalt of Hawaiʻi Island. Protecting these new habitats and planning for future scenarios can reduce potential impacts to both people and nature.
The communities in west Hawai’i have a rich culture that is strongly connected to their coastal waters, both socially and economically. Sea level rise and coastal erosion directly threaten these communities and the livelihoods that they depend on including marine fisheries and tourism. Tourism on the island, a major economic driver throughout the state, was a $14 billion industry with eight million visitors to the region in 2014. These numbers continue to grow. Visitors come to Hawaiʻi to enjoy its beautiful natural landscapes via SCUBA, snorkel, hiking and visiting parks.
The coastal infrastructure in the region is comprised of valuable ports and harbors as well as resorts that house the multi-million-dollar tourism industry. Harbors, airports, roads, and resorts will be the most at risk coastal infrastructure in the region.
Commercial fishing is another incredibly important economic asset to west Hawai’i as commercial fish landings for the island amounted to more than $100 million in 2014. While harvest is offshore, the harbors and associated infrastructure that supports the fishery are the most at risk.
Any disruption to the coastal environment of west Hawai’i can have devastating impacts on the community and the local economy.
Habitats and Species
Anchialine Pools: Loko ‘Opae ‘Ula
Hawaiʻi Island is young. So young, in fact that it’s still being created; three out of five of the shield volcanoes are still active, and one has been continuously erupting for over 30 years. The brand new geology of Hawaiʻi Island means that its foundation is constructed of a highly porous basalt. This acts as a sponge, supporting an enormous freshwater aquifer which is elevated above sea level. We get a glimpse of this phenomenon at low-lying areas where the water breaks the surface. These habitats are called anchialine pools, or loko ‘opae ‘ula, and they hold immense significance both culturally and biologically. In addition to being a source of food and freshwater in some dry areas, they are a crucial home to a unique ecosystem. From tiny red shrimp (see ‘Opae ‘Ula below) to birds, plants, snails, and insects, anchialine ecosystems support a broad array of indigenous and endemic species in West Hawaiʻi.
Utilizing the highly productive nature of estuarine environments, some coastal anchialine pools and inlets were constructed into fishponds by the Hawaiian people. These particular freshwater areas have a connection to the ocean so that water can flow outward and fish can take refuge in the safe, brackish habitat inside. This traditional form of aquaculture has been used in Hawaiʻi for hundreds of years, and many ancient fishponds still exist or are being restored for use today. By modeling the potential impact of sea level rise, we can plan how to maintain these crucial areas for the benefit of human and natural systems alike.
Coral Reefs & Intertidal zone
West Hawaiʻi is home to some of the largest continuous stretches of coral reefs in the state. Often referred to as the rainforests of the ocean, coral reefs are a hotspot for biodiversity. They also provide shoreline protection from major storm events and are a crucial source of food for local communities. Coral reefs hold immense significance in Hawaiian culture, not just because they are a primary source of food, but they are also a pivotal part of the Kumulipo, the Hawaiian story of creation. In the Kumulipo, the coral polyp was the first life created, and as such, all other living things are descended from it. This ancestral connection to the corals themselves underlines the significance of corals; not only as the foundation of reef ecosystems, but as the livelihood of the people living near them.
In addition to coral reefs, West Hawaiʻi has a productive intertidal zone which still feeds local people to this day. Opihi (limpets), Haʻukeʻuke (urchins), and limu (seaweed), are a few of the many resources still harvested at the shoreline. As sea level rises and shorelines recede, it is possible that these habitats will move inland with the rising water line. However, coastal development and shoreline stabilization efforts may prevent this, and it is important to be able to plan for sea level rise scenarios in order to protect future habitat.
Spotlight on Opae ‘Ula
Opae ‘ula are small red shrimp that are native to freshwater habitats in Hawaiʻi. Although they are typically less than 1cm in length, these little shrimp are the dominant species of the anchialine pool ecosystem. They are important grazers within the ponds. Invasive fishes such as tilapia or guppies can prey heavily on the opae ‘ula, allowing for thick algal or cyanobacterial mats to build up in their absence. Controlling the spread of invasive species can help to keep the anchialine pool systems in balance, which in turn provide food and freshwater for people and other animals.
Opae ‘ula only live part of their life in the sunlit ponds. Much of their life is spent underground, in the endless maze of cracks and crevices that hold the islands’ aquifers. Emerging only to graze on algae and bacteria, the opae ‘ula have been documented to colonize new ponds by navigating through tiny crevices under the earth.
Opae ‘ula are not only important for a well-functioning ecosystem. They also have a role in traditional sustainable fishing practices in Hawaiʻi. Opae ‘ula were harvested from the pools to be used as bait for Opelu, a type of mackerel found close to shore. The opae ‘ula were collected and mixed with red dirt or cinder to deploy from a canoe. It is believed that the dark color of the bait attracted the opelu, who mainly relied on visual cues for food, while not drawing in predators like sharks that relied on smell. Opelu fishing was highly seasonal, and harvesting them from February to June was kapu (forbidden) as they grew and spawned. During this time many fishermen would propagate the opelu schools by feeding them from their canoes using the opae ‘ula mixture. After caring for the opelu schools during the closed season, the Hawaiians would harvest the opelu from July to January. This concept of open-ocean farming is one of the traditions that made Hawaiians prosperous. Some families cared for the opelu koa (areas where opelu would aggregate) for generations, a practice that is still carried on in some areas today.
By modeling the extent of sea level rise, coastal migration, and wave run-up, we have the ability to plan for the future. Areas of future wetland habitat can be protected. Developers and planners can make more informed decisions about coastal construction. Fishpond practitioners can plan restorative work that will take into account future water levels. Having a comprehensive model of future scenarios will allow people and nature to persist alongside one another throughout the decades to come.
Data Collection, Modeling, and Design Team
- The Nature Conservancy
- National Oceanic and Atmospheric Administration
- University of California Berkeley
- NOAA Sentinel Site Program
- Hawai‘i County Planning Department
- University of Hawai‘i at Hilo
- Ala Kahakai National Historic Trail, National Parks Service
- University of Hawaiʻi Sea Grant
- US Dept. of Agriculture/Natural Resource Conservation Service
- Mauna Kea Soil and Water Conservation District
- Hawaiʻi Dept. of Land and Natural Resources, Office of Conservation and Coastal Lands