Cleaning Up Hilo Bay

UH Hilo’s Pacific Aquaculture and Coastal Resources Center’s project harnesses the power of native oysters to improve water quality

Copy Editor Rosannah Gosser

Located just after Hilo Bay’s breakwater meets Keaukaha is the University of Hawaiʻi at Hilo’s Pacific Aquaculture and Coastal Resources Center (PACRC), where an old wastewater treatment center has been converted to developing land-based mariculture systems. The center’s most recent project involves cultivating native species of oysters through aquaculture farming. As filter feeders, oysters remove excess nutrients and sediments from water, and PACRC’s research trials in Hilo Bay aim to harness this potential while restoring the health of the marine ecosystem and developing East Hawaiʻi’s coastal resources.

The research trials are also now in the process of expanding to Pearl Harbor on Oʻahu, where the U.S. Navy is working with PACRC to develop a pilot test replicating the models from Hilo Bay in order to continue studying the use of native shellfish for water quality improvement. Maria Haws, the director of PACRC and an associate professor at UH Hilo, described the project’s plans to aggregate oyster populations so that they can simply “do their thing:” improving water quality off of Hawaiʻi’s shorelines while restoring vitality to populations of native species.

The coastal waters around the Hawaiian islands should generally be clear, according to Haws, but about 80 percent are defined as “impaired,” a category set by the U.S. Environmental Protection Agency for bodies of water that do not meet water quality standards. Terrestrial runoff from areas of human habitation and agriculture carry harmful pollutants out into the ocean, and these contaminants, particularly chemicals used for fertilizer like nitrogen and phosphate, cause abnormal amounts of algae to grow. Native oysters, such as the species that the project focuses on, filter between 20 and 45 gallons of water per day in order to eat the very algae that grow on water contaminants.

“One of the species we’re interested in is black-lipped pearl oyster, or Pinctada margaritifera, which is the species that was in Pearl Harbor originally,” states Haws. “The historical record shows that there were a lot of oysters, more than you would ever see in Hawaiʻi now.”

Pearl Harbor was chosen as the site of the project’s pilot test for a number of reasons, according to Haws. As one of the largest estuaries in Hawaiʻi, Pearl Harbor holds the potential for a lot of shellfish-related biology and is home to the U.S. Naval Base Pearl Harbor, where many of the U.S. Navy’s environmental study projects are taking place. The harbor’s three lochs, the West Loch, the Middle Loch, and the East Loch, host distinct populations of shellfish, particularly those of native species like the black-lipped pearl oyster.

Containing the oyster populations within military-owned areas protects both the integrity of the experiment and people from collecting and eating potentially contaminated shellfish. Across the island from Pearl Harbor lies the Marine Corps Base Hawaiʻi on Kaneohe Bay, where similar environmental study projects help provide additional resources for monitoring the oysters.

While the shellfish are deemed inedible for now, the project also investigates whether or not the populations could be used for aquaculture farming and sold for local consumption, such as the oysters cultivated by PACRC’s Student Aquaculture Workforce training program. One of the largest applied learning programs at UH Hilo, the cooperative is operated in part by paid student workers who earn money generated from the oyster crop’s revenue while gaining experience in their field.

“This has been a really great opportunity for me to develop hands-on skills,” says Daniel Wilkie, a research manager for the training program. “It’s also allowed me to refine my ability to teach these concepts to students who are a bit new to learning them. I really enjoy the aspect of helping them develop their career and giving them useful skills that they can use when they graduate, and hopefully helping them find opportunities like I did after I graduated.”

Wilkie has worked on several projects at PACRC, including one known as the “oyster fattening system,” where oysters are produced with high glycogen stores to be sold on the market. He has also been involved with the project breeding native species of oyster to improve their restoration in the wild.

Bred as they would be in a commercial shellfish hatchery, the native oysters are raised from larvae that can only be seen clearly under a microscope. Once oyster larvae attach to a grain of sand, they are called spat and will grow a foot and synthetic eye after three or four weeks before settling on sand or rocks. After a year, the oysters are still only about the size of a dime.

The populations kept in PACRC’s experimental farm out in Hilo Bay reside inside the breakwater; here, cages containing adult oysters are suspended from hanging lines and monitored by researchers. Haws states that the experimental farm also looks at whether or not the oysters in the bay will actually create habitat for marine organisms, instead of just a temporary feeding spot for schools of fish, helping to restore the health of Hilo Bay’s marine ecosystem.

One of the most significant factors that has led to the decline of Hilo Bay’s water quality is the use of cesspools, which collect liquid waste and sewage underground in pits that frequently seep into the water table and eventually wash out into the bay. A Report to the Legislature by the State of Hawaiʻi’s Department of Health estimates that there are about 50,000 cesspools are located on the Big Island, more than Kauaʻi, Maui, and Oʻahu combined, and that about 8,7000 of them are in Hilo.

“It’s one of our dirty little secrets in Hawaiʻi,” says Dr. Steven Colbert, an associate professor of marine science at UH Hilo. “Sewage is a nasty cocktail of nutrients, viruses, bacteria, cleaning solutions, traces of pharmaceuticals, and anything that goes down your drain. The nutrients may be taken up by algae, but there’s all that other stuff too.”

Marine scientists from UH Hilo, including Colbert and his colleague Dr. Tracy Wiegner, have been working on a project in collaboration with the Pacific Islands Ocean Observing System to operate a water quality buoy in Hilo Bay that measures conditions in the water. Colbert says that they have been sharing information with Haws for the oyster farm project in order for the researchers to gauge how the bay’s water conditions are being affected by things like climate change.

Colbert emphasizes the importance of addressing the issue of Hilo Bay’s water quality from a variety of angles, including improvements in the treatment of sewage and stopping the use of cesspools.

“There’s no one solution, but working all together we can help improve the health of Hilo Bay,” says Colbert. “When we improve the health of Hilo Bay, we improve the health of our community.”

While the water quality buoy was damaged by flooding during Hurricane Lane in Sept. 2018, it’s projected to be back in operation within the next few months, according to Colbert, and will continue to provide PACRC and the public with water quality measurements, such as temperature fluctuations, salinity, and turbidity, as well as levels of chlorophyll that indicate how much algae is growing in the water. As PACRC’s experimental farm continues to propagate native oyster populations, the levels of chlorophyll are anticipated to decrease and, ultimately, increase the clarity and quality of the bay’s marine ecosystem.