Study: Can Oysters Improve Water Quality in Pearl Harbor?

Oyster cages used at Kualoa Ranch fish pond will be used in the Pearl Harbor study. Photo courtesy of DLNR.

The DLNR Division of Aquatic Resources (DAR) and Kualoa Ranch are conducting a study to see how oysters might positively impact the water quality of O‘ahu’s iconic Pearl Harbor. The study follows positive results seen with oyster populations in places like Chesapeake Bay on the East Coast.

Pearl Harbor is the largest natural estuary in Hawai‘i, and historically has been an important fishery and breeding area for a variety of fish species and other forms of aquatic life. It the past, it has supported a large native oyster population (Pinctada radiada), and an introduced species (Crassostrea virginica) between 1860 and 1920.

Oysters populations in the bay have been compromised due to excessive harvesting during the era of the Hawaiian Monarchy and sediment runoff from changing land use during the mid-1900s. Now, the presence of sediments, petrochemicals and heavy metals in Pearl Harbor pose further challenges to their survival.

But researchers want to repopulate Pearl Harbor with oysters in an effort to remedy the water’s ecosystem, and determine how well populations can survive. Oysters remove microorganisms and nutrients from the water column, improve water clarity and light penetration for other species to thrive and, prevent oxygen depletion. Their presence, as observed in Chesapeake Bay and other areas, provides a substantial revitalization of the environment they inhabit.

The study will gather data on Pearl Harbor’s water quality, oyster growth rates and possible accumulations of various chemicals, such as PCBs, and certain metals in their muscle tissues. Oysters will be introduced in the bay inside floating cages to protect them from predators and harmful sediments as they grow, and optimize their natural filtration capabilities. The U.S. Navy is providing access to the area in Pearl harbor where the study is being conducted.

Dr. Bruce Anderson, DAR administrator, designed the floating cages, which are also used at Moli‘i fish pond at Kualoa Ranch, where Anderson and ranch owner John Morgan are growing oysters for public consumption.

A specific species of oyster, Crassostrea gigas, is being used in the project because they have shown strong survival and growth rates in Hawaiian fishponds.

Through the study, DAR will determine to what degree Pearl Harbor’s waters can support oyster population growth, and the feasibility of expanding the project as a future bioremediation effort.

“I grew up digging oysters in Pearl Harbor, so I’m eager to see the results of this innovative project,” said Gov. David Ige. “I hope the oysters can help clean up the water in the harbor to create a healthier environment for future generations.”