On a recent sunny morning at the University of Hawaii at Hilo’s Pacific Aquaculture and Coastal Resources Center in Keaukaha, research manager Daniel Wilkie showed off a spat of small but growing oysters, each not much bigger than a pebble.
They might not look like much, but eventually they will do important work cleaning Hawaii’s waters.
The U.S. Navy, Oahu Waterkeeper and PACRC joined forces earlier this year to use native species of shellfish to improve water clarity and quality in Pearl Harbor estuary.
According to a news release issued in February from UH-Hilo, the project builds on a successful feasibility study conducted by the state Department of Land and Natural Resource Division of Aquatic Resources, using Pacific oysters, a non-native species, as a tool to improve clarity and quality of waters within Pearl Harbor.
While the Pacific oyster survives and grows well in Pearl Harbor, and it may continue to be used for bioremediation, the new project will focus on native shellfish species because of their deep cultural significance.
The first spat of native oysters was deposited in Pearl Harbor in early June.
PACRC director Maria Haws said the center teamed up with Waterkeeper, an environmental organization that works to protect bodies of water, about two years ago after the first Hawaii chapter was established.
“And one of the things we wanted to do is use shellfish to clean the water, but the shellfish is also obviously very interesting and attractive to people, so it increases awareness,” she said. “Then once you’ve raised awareness with people, you can get them engaged in community-based action to help clean the water.”
PACRC provides technical advice and produces the oysters and other shellfish needed for the project. The center also is working to develop seaweed for similar purposes.
Most bivalves are filter-feeders, Haws said, which means they pump water and extract the phytoplankton in it.
“The reason that cleans up the water is most of our water in Hawaii is not supposed to have too much phytoplankton, it should be very clear,” she said. “That’s (where) coral grow. They grow in very clear water that the sunlight can penetrate. Most of the waters in Hawaii that are cloudy or muddy, it’s not naturally like that. It’s because of impacts.”
When inorganic nutrients found in fertilizer, like nitrogen, phosphorous and potassium, runs off the land and into the water, Haws said it fertilizes the algae, leading to dense algae blooms, “which are not natural in Hawaii. That’s perfect for oysters, though.”
Native oysters can filter between 20 and 45 gallons of water per day, depending on their size.
Approximately 500 oysters were deposited in Pearl Harbor.
In addition to Pearl Harbor, native oysters also been placed at the Marine Corps base at Kaneohe Bay on Oahu and in the Ala Wai boat harbor, also on Oahu, in partnership with the Hawaii Yacht Club.
“It’s just a small test because whenever you start these projects, you don’t want to put out like 10,000,” Haws said. “You put out just a few to make sure they’re going to do okay, and then you build up from that.”
Haws has since checked on the placed oysters.
“The first thing you want to do is see did they live? And they mostly lived,” she said. “In fact … we were concerned about putting out really small ones and they had done really well. They had hardly any mortality. They were around 1.4 millimeters when we put them out and some were over probably 10-12 millimeters. This is in two weeks only.”
Measurements tell the researchers whether the oysters are growing well or not.
But the recent projects are just the latest in PACRC’s work with oysters, which began a decade ago.
In 2009, Haws said Pacific oysters were tested in the Keawanui fish pond on Molokai and He‘eia pond on Oahu.
“The intent here was more for aquaculture and food production, but we knew that even if the ponds would not be able to pass the (state Department of Health) growing area classification process, the oysters would be beneficial for water quality purposes,” she said. “He‘eia was our original partner in the native oyster effort as that is where we first found them …”
Pacific oysters were first put into Hilo Bay in 2013 as part of a joint research effort between the center and Goose Point Oyster Co., and native oyster were tested starting in 2015, Haws said. Native oysters also were tested at the Hale O Lono fishpond in Keaukaha.
“We will continue producing native oysters as long as we have funding and personnel to do so, which should be for many years,” Haws said. “We are also planning to work with other native species of shellfish, including pearl oysters, which we have now, pen shells and some clam species.
“Our plan, assuming the partners agree, is to expand on the size of the current projects so that the bivalves have a significant impact on water quality,” she continued. “We most likely will expand to other sites.”
The oysters shown by PACRC’s research manager Wilkie, a former UH-Hilo student, were native oysters being grown for the center’s current water quality projects.
“Personally, there’s a great sense of gratification from knowing that our goal here is to put the native species back in the water for restoration purposes,” Wilkie said. “So that’s incredibly gratifying and it feels good to know that I’m contributing back to the community by reinvigorating the native species here, because we know with invasive species and over-collection, a lot of the Hawaiian reefs are dramatically different from the way they used to be. So any way we can try and restore the natural habitat is incredibly (justified).”
Haws said native oysters are also edible, “so if more farming areas can be approved, they could be cultured for consumption here.”
According to Haws, PACRC has several tanks approved by the DOH, “so we could grow them here for consumption, (but) we just don’t have enough to go around right now, so we’re giving all the ones we have to the Waterkeepers, Navy, Marine Corps, etc., as they are funding the production.”
Haws said about 10 UH-Hilo students, as well as recent graduates, are working on the native oyster project.
Email Stephanie Salmons at firstname.lastname@example.org