Restoring an Estuary

"When the Mangrove is Removed the Natives Can come Back." 

Kanekoa Kukea Shultz 

TNC marine coordinator for Kāne‘ohe Bay.  

By Jan TenBruggencate

Kanekoa Kukea Shultz has been working for more than a decade to help restore windward O‘ahu’s He‘eia ahupua‘a. To inspire community and financial support for the project, the 40-year-old biologist carries with him a historical 8 x 10 photograph—a 1928 aerial image of He‘eia that depicts fresh water streams from the Ko‘olau Mountains flowing across a wetland of neatly planted taro fields, through a rock-walled Hawaiian fishpond, out onto the reefs of Kāne‘ohe Bay.

“When you see He‘eia as it once was—a fully functioning ahupua‘a—you realize it can be that way again,” said Kukea Shultz, the Kāne‘ohe marine coordinator for The Nature Conservancy and executive director of Kāko‘o ‘Ōiwi, a community group managing the wetland.

Restoring an ahupua‘a—an interlinked series of environments running from mountain to sea—is a complicated endeavor. The latest challenge is to restore the He‘eia estuary, a task that requires removing 13-acres of invasive mangrove trees. Tall, dense non-native red mangrove stands are creating a dam that prevents the natural movement of fresh water, native fish, shrimp and other aquatic species between the sea and He‘eia’s broad wetlands and mountain streams.

Alien in the Landscape

Mangrove is prized in many parts of the world, but in the Hawaiian Islands it is an alien in the landscape, outcompeting native plants, blocking aquatic migration and creating a dense, low-oxygen zone where native species can’t thrive.

“It is a source of sediment. The massive root structure collects leaves that rot in place—at least 100 tons of leaf litter a year. And it creates a high canopy shade. The result is that a lot of native species are not found in mangrove in Hawai‘i,” said Kukea Shultz.

When completed, the mangrove removal should restore the two-way transport of aquatic life, allow fresh water to flow freely to the sea, improve the productivity of the fishpond and help revitalize the brackish estuary for which He‘eia was once famous.

 “When the mangrove is removed, the natives can come back,” said Kukea Shultz.

The removal is part of the larger He‘eia Restoration Project, a community-led partnership to restore the ahupua‘a initiated by the Ko‘olaupoko Hawaiian Civic Club. It includes clearing invasive grasses choking the streams, re-establishing the area’s lo‘i kalo (taro ponds), rebuilding irrigation channels, and restoring He‘eia Fishpond.

Partnering with the Community

The Nature Conservancy has been a partner in He‘eia for more than a decade, working with the State’s Division of Aquatic Resources and University of Hawai‘i to remove invasive algae from Kāne‘ohe Bay, and with Kāko‘o ‘Ōiwi to restore He‘eia’s wetland taro system and reduce sediment flowing onto the reef.

Other partners include Papahana Kualoa, which is working with the native plant nursery Hui Kū Maoli Ola to restore the He‘eia uplands; and Paepae O He‘eia, which is restoring the vibrancy of the 88-acre He‘eia Fishpond. The Hawai‘i Institute of Marine Biology in Kāne‘ohe Bay provides scientific and administrative support through the new National Estuarine Research Reserve (NERR).

The strength of the partnership is a major reason the National Oceanic and Atmospheric Administration recently named He‘eia a NERR, a designation of importance that brings with it federal funding for research and education. Additional support from NOAA is enabling the mangrove removal, with grants from the U.S. Fish and Wildlife Service and State Department of Land and Natural Resources also helping to fund restoration work. Each of these grants requires matching funds, and The Nature Conservancy is actively soliciting private donations for this project.

“It all adds up to a watershed that is actively managed from the ridgeline to the outer reef,” said Kukea Shultz.

Native Travelers

He‘eia has two species of invasive mangrove—Rhizophora mangle and Bruguiera gymnorrhiza—that are interfering with the movement of native species through the He‘eia ecosystem.

Those native travelers include five ‘o‘opu—the Hawaiian native goby fish—and native shrimps and snails that travel back and forth from fresh water in the upland streams and ponds through the brackish estuary and out to the salt sea.

There are also fish species like the āholehole (Kuhlia malo) that inhabit the coastline and Heʻeia’s semi-salty estuary. And, native birds like the ‘alae ‘ula (Hawaiian coot) and ‘alae ke‘oke‘o (Hawaiian moorhen), use the wetland streams and lo‘i kalo.

Contractor Pono Pacific Land Management is leading the mangrove removal and is on track to clear the first six acres by summer. Leaves and branches will be burned or mulched for use in the ahupua‘a. Useful timber will be set aside for use by the local community for projects like building traditional structures. Community work days will involve volunteers in the effort.

“Restoration of the mouth of He‘eia stream is key to increasing coastal resilience, restoring the ecological function of the watershed, and improving fisheries in Kāne‘ohe Bay. The goal is to get back to the point where we’re producing food for people, habitat for the fish and the birds, and restoring the environment,” said Nature Conservancy Marine Science Advisor Kim Falinski, who is leading monitoring efforts during and after the mangrove removal.

Re-establishing Connectivity

The recovery will not be instantaneous. According to Falinski, it could take up to three years for the oxygen levels to come back and fish to return. “As the roots decompose, we expect the sediment level to sink back to its original elevation,” she said.

That should allow salt and fresh water to mix in the estuary, as they did before the mangrove. Once the mangrove is gone, teams will replant the area with native wetland species like ‘ae‘ae (Lycium sandwicense) and ākulikuli (Sesuvium portulacastrum), recreating the habitat that historically existed there.

“Our goal is to re-establish connectivity all the way mauka,” said Kukea Shultz. “The reef fish are already becoming more plentiful because they have a refuge in the stream mouth. The ‘o‘opu can utilize the channels we’re creating.”

In addition to restoring the ecosystem, the He‘eia partnership seeks to restore food production to the region—including kalo, which is already being grown and sold, and fishes from the fishpond and nearshore ocean environment.

Hi‘ilei Kawelo, executive director of Paepae o He’eia, said the work done to date is already improving the productivity of the fishpond.

“We always talk about the health of the fishpond only being as good as the health of the whole system. The fishpond is part of this estuary. When I walk on the (fishpond) wall, I’m seeing schools and schools of fish inside and outside the fishpond,” she said.

A long-term goal of the partnership is to perpetuate cultural agriculture and aquaculture practices so they can be taught and used elsewhere in the Hawaiian Islands. Much works remains to be done. But Kukea Shultz is already anticipating the day when, just like in the photograph he carries, the mangrove is gone and there is an unimpeded view and flow of water from the mountains to the sea.
 

GET TEXT UPDATES*

Stay Updated

Learn about the places you love and find out how you can help by signing up for Nature eNews.

I'm already on the list Read our privacy policy

Thank you for joining our online community!

We'll be in touch soon with more Nature Conservancy news, updates, and exciting stories.