Restoring Habitat for Marine Life in Kāne‘ohe Bay

Invasive algae is cleared and donated to local farmers for use as fertilizer and compost. 

Fed by freshwater streams that create rich estuarine habitat, windward O'ahu’s Kāne'ohe Bay is the largest bay in the main Hawaiian Islands and lays claim to O'ahu’s only active fishponds. This urban oasis at the foot of the Ko‘olau Mountains harbors coral reefs, sand flats, and seagrass beds and provides refuge for green sea turtles, migrating whales, birthing sharks, foraging manta rays, and resting spinner dolphins.

But a closer look reveals the bay’s marine life can’t withstand the direct and indirect pressures of an increasing population. Overharvesting, invasive algae, and sediment flows have taken a particularly severe toll on its reefs and fish populations.

To improve their ability to recover, the Conservancy partnered with the State and the University of Hawai‘i to rid the bay of a non-native algae introduced for aquaculture in the 1970s. Without natural predators, the algae quickly spread and began smothering and killing the bay’s coral reefs that pāpio, ‘ōmilu, he‘e and other marine life rely on for food and shelter.

Using custom-made underwater vacuums, crews and volunteers removed 160 tons of algae, clearing nearly 40 acres of reef in just three years, then reintroduced native sea urchins that graze the reefs to prevent regrowth. By 2015, the unwanted algae on some reefs was reduced by 99% and disappeared entirely from others.

These changes significantly improve conditions for native algae regrowth and—together with efforts in the He'eia wetlands to reduce sediment flows—improve our chances to once again see a healthy bay with thriving marine life.