There's good news on the invasive species front: introduced mangroves on the Big Island are under control and most of them are gone. Thanks to the efforts of Malama O Puna (MOP) volunteers, the red mangrove, or Rhizophora mangle, is close to becoming a problem of the past at four sites in Puna, one near Hilo and one in Kona.
This species of mangrove is a coastal tree native to South America, Florida and the West Indies. Sugar plantation owners introduced it to O'ahu over 100 years ago to help "stabilize massive erosion caused by poor farming practices," according to the Big Island Red Mangrove Eradication Project. While mangroves serve a beneficial purpose in their native environments by providing habitats for fish and by protecting coastlines from erosion caused by wave action, their presence in Hawaii threatens our native plants and animals and makes coastlines inaccessible to humans because of their numerous branches and prop roots.
Mangroves have "replaced native coastal forests and pristine coastlines with vast expanses of anaerobic muck, in which nothing else can grow," according to nonprofit organization Malama O Puna. This group also reports, "mangroves contribute to decreased water quality by dropping large amounts of organic matter, resulting in conditions that favor alien fish and exclude coral and related organisms. Mangroves also choke out native vegetation and destroy nesting habitats for all four Hawaiian endemic shorebirds."
Alula Bay Project
The successful mangrove eradication project at Alula Bay is "our poster child," said Ann Kobsa, project manager. This area of Kona is state-owned land adjacent to Kaloko-Honokohau National Historical Park and has much historic and archaeological significance. It includes over 20 anchialine pools, which are landlocked bodies of water connected to the ocean by subterranean passages. Malama O Puna joined forces with the Big Island Invasive Species Committee (BIISC), the Pacific Coast Joint Venture (PCJV), the Hawai'i Fish Habitat Partnership and the International Union for the Conservation of Nature (IUCN) to bring this historic area back to its pre-mangrove condition. And they accomplished this feat through manual eradication, using chainsaws, sickles and lots of elbow grease.
Mangroves were not the only invasive aquatic plant to choke the pools at Alula Bay: pickleweed, or Batis maritima, formed dense mats over most of the pools. Kobsa reports that removal of both types of plants is expected to result in "improved water flow and reduced salinity in pools, increased oxygen levels," and the return of pool plants and animals, including endangered orangeblack damselflies and the red shrimp that once populated the ponds. Endangered shorebirds such as the Hawaiian stilt are likely to return and build nests. Kobsa added, "We hope the Hawaiian coot, moorhen and duck will also return."
Of cultural importance is a heiau that was uncovered during the process of mangrove removal. Kobsa praised "the support of a group of women that continue to utilize the temple for the practice of their ancestral spiritual faith," which was vital to the project's success. She went on to relate, "They brought us food every day and one came and helped out several days, working very hard. They related that the heiau was for healing, which may explain why our usual aches did not bother us while we were working there."
In an email, Kobsa shared, "I wish you could have been there to feel it because I am at a loss to describe the energy of the group and the place... the entire group agreed the experience would be one they would never forget."
Visitors to Alula Bay are reminded to treat the area with respect by not disturbing or removing any rocks or other objects and by packing out any trash they find.
Kobsa's report concludes with this good news: "The pools are being restored to health following eradication of the mangroves and the entire coastline of our island is protected from mangrove invasion. Additionally, the eradication is expected to benefit the entire coral reef ecosystem, as the nutrient loading caused by mangroves and the alien birds that roosted in them is eliminated."