Along with Pearl Harbor, Marine Corps Base Hawai‘i is one of first military bases in Hawai‘i to partner with O‘ahu Waterkeeper, an environmental non-profit, to deploy cages of native oysters for water quality improvement. Usually, the most widely known benefit of oysters is their aphrodisiac quality, but these invertebrates may in fact hold the key to cleaner water surrounding the Mokapu Peninsula.
So, why oysters? Oysters are notorious water filters. They’re nicknamed “ocean vacuum cleaners” or “pool pumps of the sea” because of their filter-feeding habits. These amazing bivalves (“bi-valve” meaning two shells hinged together) naturally feed on phytoplankton, algae, and other microscopic organisms, and remove suspended solids, harmful pollutants, and nutrients from the water column. Because oysters and clams collect toxins and contaminants in their tissues, State law and base regulations prohibit the taking and consumption of these mollusks. The process of filter feeding results in cleaner water which can, in turn, positively impact other aquatic species. Oysters essentially purify the water as they grow and sequester nitrogen and CO2 from the atmosphere. A single Pacific oyster can typically filter 50 gallons of water in 1 day. The O‘ahu Waterkeeper project on KBay differs from the others by using native oysters endemic to Kaneohe Bay instead of employing the Pacific Oyster, which is native to Japan and Asia, to accomplish the goals of improving water quality and clarity in the surrounding waters. Bivalve filtration rates vary according to many factors (size, temperature, available food, etc.), but it is estimated that the native oyster species utilized for this project have similar filtration rates to its Pacific relative and will be equally effective in removing harmful pollutants. Lance Bookless, Natural Resource Manager for MCBH Environmental Division, understands the benefit of such restoration projects. “The hope for Marine Corps Base Hawaii,” Bookless says, “is that a few cages of oysters, strategically placed, can be the start of an entire bay restoration and living-reef project.”
A partnership with the University of Hawai‘i and the Waiwai Ola Waterkeepers Hawaiian Islands organization has deployed 3 mesh cages within base jurisdiction to test whether oysters can survive and ultimately improve the health of the surrounding water. The purpose of the plastic cage is to protect the oysters from predators (and people), while simultaneously allowing for more effective reproduction through the aggregation of oysters in multiple areas. The cages are placed approximately 2 - 3 feet below the surface so they are not exposed by the tidal changes. The cage’s mesh sides allow water to flow freely in and out of the cage but still avoid any oyster loss in the process. The oysters will then be counted after a trial period, of about 6 months, and if the survival rate is high, the project will be expanded accordingly.
The technique of using oysters to clean polluted water, is already utilized across the globe. The MCBH project, in particular, builds on the successful feasibility study conducted by the Department of Land and Natural Resources (DLNR), Division of Aquatic Resources (DAR) on the use of the Pacific Oyster (Crassostrea gigas), as a tool to improve quality and clarity of waters within Pearl Harbor in 2017. There is now a tracked history of the successful use of bivalves both for farming and for water quality mitigation purposes in Hawai‘i.
1,000 Hawaiian Oysters (Dendostrea sandvicensis) and Black-lipped Pearl Oysters (Pinctada margaritifera) will be deployed in Kaneohe Bay to help remove sediment, bacteria, heavy metals, PCBs, oil, microplastics, etc. While the Pacific Oyster survives and grows well in Hawai‘i waters, O‘ahu Waterkeeper prefers to use native oysters because of their unique cultural value and in hopes of replenishing and restoring these species to the local ecosystem. Wendy Wiltse, marine biologist and O‘ahu Waterkeeper Board President, says she hopes to see the native oysters spawning. “(This) project will help not only restore the biodiversity and health of the ecosystem,” Wiltse states, “but will ultimately increase the native oyster populations in Kaneohe Bay.” Native oysters were once abundant and were a part of many ancient Hawaiian chants, songs, and legends. Sadly, their numbers have declined steadily over the last century. This project is part of a series of restoration efforts for this valuable marine resource.
As you may imagine, these oysters will not be ideal for eating after absorbing all of those pollutants, as their primary purpose will be improving water quality and clarity. Across the islands, there are 200 native bivalve
species that, historically, could be found readily in Hawaiian waters and are now extremely rare. While these native oysters are traditionally smaller in size, each species offers specific strengths (volume filtering, pollution targeting, etc.) and that can help scientists understand which type of mollusk to use for different restoration projects and locations. The long-term project could potentially educate biologists on future ecosystem-rebuilding techniques and is an opportunity for the general public to learn about the health of our waters. The Waterkeepers are currently working on an environmental education curriculum that utilizes the native oysters to share important information about water quality. Rhiannon Tereari‘i Chandler-‘Iao, Executive Director of the statewide Waterkeeper organization, elaborates, “we want children to be able to visit the oysters and learn about environmental issues such as stormwater, wastewater, water quality and fishing safety.”
If you have additional questions or concerns on this project, call Base Environmental at 257-7000 or 257-7129.