UH Hilo graduate student Bryan Tonga initiates first comprehensive study ever done on nearshore water quality in Micronesia

Findings from the research will contribute vital information to climate adaptation efforts in Pohnpei and other tropical Pacific island nations, allowing them to better manage their coastal waters, improve water quality, and reduce damage to coral reefs in the face of climate change.

By Leah Sherwood.

Four people standing fro photo: Tracy Wiegner, Bryan Tonga, Karla McDermid and Steven Cobert. Standing in front of trees.
UH Hilo graduate student Bryan Tonga stands with his thesis committee, all professors from the marine science department. From left, Prof. Tracy Wiegner, Tonga, Prof. Karla McDermid, and Assoc. Prof. Steve Colbert. Photo by Raiatea Arcuri for UH Hilo Stories.

A graduate student at the University of Hawai‘i at Hilo has been collecting data to assess nearshore water quality and its effect on coral reefs in the island state of Pohnpei, the capital of the Federated States of Micronesia. FSM is an island nation in the Western Pacific situated south of Guam and east of the Philippines.

Bryan Tonga in lab
Bryan Tonga, in 2017 as an undergraduate, weighs out samples for analysis on the Isotope Ratio Mass Spectrometer, UH Hilo Analytical Lab. Courtesy photo.

Bryan Tonga, who is from Pohnpei and a graduate student in the UH Hilo tropical conservation biology and environmental science program, says he and his colleagues are evaluating sewage pollution using a multi-indicator approach.

“We are measuring salinity, turbidity, nutrients, nitrates, and fecal indicator bacteria levels in the water,” he explains. “We also sampled macroalgae for stable nitrogen isotopes and nitrogen content.”

Tonga has spent the past two summers in Micronesia collecting water and macroalgae samples from 31 stations around Pohnpei’s coastline, including both populated and pristine remote areas, which are difficult to reach due to the mangrove forests covering most of the island’s coast. His work is the first comprehensive documentation of the water quality conditions on Pohnpei’s coastline.

He says the macroalgae get their nutrients from the water column.

“In order to figure out if the macroalgae are getting nutrients from sewage pollution in the water, we’re taking readings of Nitrogen-15, which has very specific values for human sewage,” he explains. Tonga notes that development along coastal areas in Pohnpei is increasing, causing more water pollution.

Managing the effects of climate change

Findings from Tonga’s research will contribute vital information to climate adaptation efforts in Pohnpei and other tropical Pacific island nations, allowing them to better manage their coastal waters, improve water quality, and reduce damage to coral reefs in the face of climate change in the region.

“We need to establish baseline water quality conditions because with climate change the water quality could shift dramatically,” says Tracy Wiegner, a water quality expert and professor of marine science who is on Tonga’s thesis committee. “In Pohnpei, like here on the island of Hawai‘i, a lot of houses use cesspools. With rising sea levels, they can become inundated with sea water and sewage can flow out to the nearshore reefs. Also, climate change could bring increased precipitation, which would mean increased land runoff to the shores and potential flooding of cesspools.”

Wiegner is the director of the Analytical Laboratory at UH Hilo, where Tonga is analyzing his collected samples. “Bryan has collected the first nutrient samples from Micronesia ever,” notes Wiegner.

Two students prepare specimens in lab.
Bryan Tonga, at right, with fellow student Sione Lam Yuen, in 2017 when Tonga was a marine science undergraduate and worked as a laboratory assistant at the UH Hilo Analytical Lab. Here, the students prepare samples for analysis on the Isotope Ratio Mass Spectrometer. Courtesy photo.

Along with Wiegner, Tonga’s thesis work is being supervised by UH Hilo marine science professors Karla McDermid and Steven Colbert. McDermid, an expert in phycology, will help Tonga identify the macroalgal tissue samples since distinct species may take up nutrients from the ocean differently.

Tonga plans to share his data with stakeholder agencies in Pohnpei such as the Pohnpei Environmental Protection Agency (PEPA), the National Food Safety Laboratory in Pohnpei, the Conservation Society of Pohnpei, and the Natural Resource Conservation Service. He says the agencies recognize the significance of his research and have responded by contributing institutional resources to support his efforts in creating baseline data for nutrients in the water.

“PEPA let me use their lab to do my readings and bacteria culturing, but they cannot process the nutrient content, so that is being done in the UH Hilo Analytical Lab,” says Tonga. “PEPA hosted me and provided me with transportation and a lab technician. They think it is really important for Pohnpei to have me doing this kind of project because the research capacity is low, and they are currently only able to do limited amounts of water quality testing.”

While in Pohnpei, Tonga also mentored Wayneheart Celestine, an undergraduate from the College of Micronesia, on water quality sampling and laboratory analyses. Celestine’s internship was supported by the Louis Stokes Alliances for Minority Participation (LSAMP) program at UH Hilo.

Tonga’s project is supported by the Pacific Islands Climate Adaptation Science Center and Hawai‘i Sea Grant. His travel in 2018 was funded by an L-SAMP grant from the National Science Foundation.


Story by Leah Sherwood, a graduate student in the tropical conservation biology and environmental science program at UH Hilo. She received her bachelor of science in biology and bachelor of arts in English from Boise State University.

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