Maunalua Bay

Island of O‘ahu

“A federal stimulus project co-managed by the Conservancy has cleared 2.9 million pounds of invasive algae from the bay.”


Nestled between two volcanic features, Koko Head to the east and Diamond Head to the west, Maunalua Bay forms a broad, eight-mile indentation in Oahu’s southern coastline. The land surrounding the bay was once a succession of valleys dominated by ranches, dairies and small coastal villages, but today it is home to a string of Honolulu suburbs and more than 60,000 residents.

Just a few generations ago, families living in the area harvested seafood almost daily from the bay. Today, Maunalua’s once productive reefs are enjoyed primarily for recreational activities such as boating, diving, parasailing, outrigger canoe paddling, stand-up paddle boarding and surfing.

Recreational fishing provides enjoyment too, but populations of culturally important marine life, such as surgeonfish, parrotfish, goatfish, eels and lobster are dramatically lower than they once were, while the native algae and seagrass that once covered the bay’s shallow reef flats have become rare.

Despite its poor condition, the bay is still frequently used by residents and visitors, whose ranks include dolphins, turtles, whales and occasionally monk seals.

Critical Threats

Three primary threats are contributing to the decline of the reefs in Maunalua Bay: overharvesting, land-based pollution and invasive species. The worst of the invasive species is an alien alga called Avrainvillea amadelpha, or “leather mudweed,” which outgrows, outcompetes and smothers native algae, coral and seagrass.

Leather mudweed is found in nearshore reefs as well as waters 70 meters deep. In shallow water, it attracts and traps sediment, forming a thick carpet that smothers the native corals and holds sediment in place. This degrades the entire reef ecosystem, displacing all other native species and creating an oxygen-poor environment that prevents native marine life from flourishing.

Avrainvillea amadelpha was first reported in Hawai‘i by scientists in the early 1980s. It has since spread along the southern shores of O‘ahu but is most widespread in Maunalua Bay, where it covers more than 54 acres.

What the Conservancy Is Doing

The Conservancy became involved in Maunalua Bay in 2007 to protect its marine resources and restore the health of its nearshore reefs. Together with the community-based organization Mālama Maunalua, the Conservancy developed a conservation action plan for the bay and began conducting volunteer alien algae clean-ups.

In June 2009, after community volunteers had removed 55 tons of alien algae from the bay, the National Oceanic and Atmospheric Administration (NOAA) announced that the project had been awarded $3.4 million through the American Reinvestment and Recovery Act of 2009 (ARRA) to scale-up the alien algae removal effort.

Managed by The Nature Conservancy and Mālama Maunalua, the ARRA project has already reached its goal -- removing 2.9 million pounds of invasive algae and reclaiming coral reef and seagrass habitat over 23 acres of the bay.

In the process, it has created or directly supported 75 jobs, provided 7,000 hours of community service through increased volunteer efforts, and stimulated green business as individuals and organizations convert the removed algae into marketable compost or fertilizer. In addition, the project has increased public awareness, built community capacity for expanded and sustained stewardship of the bay, and created a statewide model for community-based management of marine resources.

Still other benefits include a scientific monitoring program coordinated by the Conservancy to measure both the short and long-term impacts of the project on water quality, native algae, corals, sea grass and other marine life in the bay.

When completed in June 2011, the ARRA project will have enabled the Conservancy and its partners to make significant progress in addressing one of the top three threats to Maunalua Bay— invasive algae.

Going forward, the Conservancy will seek additional funds to remove the remainder of the invasive algae from the bay while supporting Mālama Maunalua’s efforts to engage fishers in establishing sustainable fishing practices in the bay, and the broader community in reducing land-based sources of pollution.


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