Kai - Sea

Marine Resources and Wildlife

Long-time Maunalua residents recall a bay rich with resources that were relatively easy to gather. Maunalua Bay became a significant commercial fishery, and boats bringing in tons of catch were common. Much of that has changed over the past 50 years. Areas covered by coral reefs have shrunk, and catching mature fish within the reef flats is challenging. Lobster and the native limu (algae) beds have all but disappeared.


Photo by John Johnson	Photo by Carol Wilcox

Though the diversity and abundance of reef species have diminished, there still remain healthy pockets of coral reefs and native seagrass beds. Honu (Green sea turtles) and even endangered `Ilioholoikauaua (Hawaiian monk seals) can be found within the bay. And koholā (Humpback whales) are common visitors that never fail to please whalewatchers.

NOAA photo

Reef Flats

Maunalua Bay is characterized by large reef flats extending well out from the shoreline to a forereef that drops to about 15-20 feet. Beyond the fore reef the sea floor gradually increases in depth, broken up by small sudden drop offs that tell the story of sudden increases in sea level rise over the past hundreds of thousands of years. One can imagine a view from space revealing the bay to be a series of broad benches leading into the open ocean.

The broad reef flat is home to a diversity of marine algae (limu) that provide food shelter for an abundance of marine life, including small juvenile fish, crabs, shrimps, sea cucumbers, and octopus. Bigger fish such as goatfish (weke, moana), bonefish (ō'io), omilu, manini and mullet make use of the channels that are carved into the reef flat to forage on these plants and animals.

Photo by John Johnson

The forereef, indicated by where the waves break in the bay, is home to the greatest coral reef growth in the bay and harbors the greatest diversity of marine life in Maunalua. Surgeonfish, butterflyfish, parrotfish (uhu), weke, eels, crabs, and many other animals rely on the corals for food and shelter. In addition, recognizable sea life like dolphins, turtles, sharks, manta rays, whales, and monk seals frequent the bay.

Native Marine Plants

Most commonly known marine plants are limu. We are fortunate that Maunalua Bay still has native limu such as limu kohu (Asparagopsis taxiformis), a native algae, that is a common part of the traditional Hawaiian diet prized for its ‘ono taste.


Limu kohu	Nenue grass

Maunalua Bay is also home to very special, and increasingly rare marine plants. Nenue grass (Halophila decipiens and H. hawaiiana), or Nenue grass, are two species of native sea grass found along the broad sand flats in Maunalua Bay. There are only three species of sea grass in Hawai`i, and Halophila hawaiiana, which is found in the bay, is endemic to Hawai`i, meaning it is found nowhere else on earth. These seagrasses are more related to the plants in our garden, than the limu in our ocean, having roots, stems and leaves. They are also food for our endangered sea turtles among other marine life. Due to pollution, habitat loss, and the spread of alien algae, beds of these special marine plants are disappearing. Fortunately, researchers from the University of Hawai'i are helping us to better understand how we can protect and restore our threatened seagrass populations in Maunalua Bay.

Alien Algae

The spread of invasive, non-native marine algae is one of the greatest threats to Hawai‘i’s coral reefs and other near shore marine ecosystems. Hundreds of alien species have been introducted to O`ahu over the past decades. Free from predation and other control measures that would be found where these species are naturally found, some of these alien species are able to take advantage of new conditions and grow rapidly. As alien algae spreads, it grows over and smothers coral reefs and native algal communities, killing extensive areas of native habitat. Lowered populations of reef fish, a result of unsustainable fishing pressure and poor habitat conditions, are unable to keep the algae in check.

Five species of alienmarine algae have shown this ability to grow and spread at alarming rates, outcompeting our native corals and limu, and so destroying native reefs. Of these five species of alien algae, three are devastating Maunalua Bay. Gracilaria salicornia (a relative to our native manauea), Acanthophora spicifera, and Avrainvillea amadelpha.

Removing alien algae from high priority coral reefs is essential to the survival of Hawaii’s reefs. Currently, we are implementing a number of measures to address this quickly growing problem.

We are removing alien algae through volunteer clean up events and use of the Mini Sucker. The more we can remove, the less there is that can grow and spread in the bay.

We can also do more by increasing the populations of limu-eating fish that will feed on some of these alien species. Native fish like manini, and even native urchins, can offer natural controls to address this problem.

Like our native limu, these alien algae species are capable of spreading through fragments. New populations can arise from a single piece broken off by wave action or trampling. For this reason, it's very important that we pay attention to our fishing, diving, and boating gear to ensure they are free of algae fragments that we can spread to new places.

Lastly, and most importantly, through broad-based partnerships and personal choices, we can reduce the large amounts of sediments and nutrients that are entering our bay that in effect fertilize these beds of alien algae.