First-of-its-kind Pohnpei coastal water quality study conducted by UH Hilo graduate student is posthumously published
The late Bryan Tonga conducted the first island-wide nearshore water quality study for his homeland of Pohnpei. His study was published March 28.
By Susan Enright.
In a meaningful tribute to a former marine science major and graduate student in the tropical conservation biology and environmental science program, marine scientists at the University of Hawaiʻi at Hilo have completed and posthumously published a study on coastal water quality in Pohnpei conducted by their student Bryan Tonga.
- Baseline conditions and land-based drivers of nearshore water quality in Pohnpei, Federated States of Micronesia (June 2025, Marine Pollution Bulletin)
Coauthors of the study are fellow student Devon Aguiar (now at the Hawaiʻi Coral Reef Initiative, Hawaiʻi Division of Aquatic Resources, Hilo Office), and UH Hilo marine science professors Tracy Wiegner, Karla McDermid, and Steven Colbert.
For his master’s thesis, Tonga conducted the first island-wide nearshore water quality study for his homeland of Pohnpei in the Federated States of Micronesia, an island nation in the Western Pacific situated south of Guam and east of the Philippines.
Tonga says in a 2020 interview that he and his colleagues were evaluating sewage pollution using a multi-indicator approach.
“We are measuring salinity, turbidity, nutrients, nitrates, and fecal indicator bacteria levels in the water,” explains Tonga. “We also sampled macroalgae for stable nitrogen isotopes and nitrogen content.”
- UH Hilo graduate student Bryan Tonga initiates first comprehensive study ever done on nearshore water quality in Micronesia (February 2020, UH Hilo Stories)
A bright and accomplished student, an unimaginable loss
Tragically, Tonga lost his life while hiking in August of 2020 during his last year of graduate school, with his thesis almost finished and one more class to complete.
The budding marine scientist had been a part of the UH Hilo marine science department ʻohana for years. As an undergraduate majoring in marine science, he was an intern in the Pacific Internship Programs for Exploring Science (PIPES) in 2015 working with his marine science professors Wiegner and Colbert, along with their colleague Jim Beets and fellow student Leilani Abaya, on a long-term water quality project in Puakō.
- UH Hilo researchers partner with Puakō community to improve human and coral reef health (June 9, 2015, UH Hilo Stories)
Tonga earned his bachelor of science in marine science in 2017. He then started the tropical conservation biology and environmental science graduate program and his Pohnpei water quality study in 2018 under the guidance of his thesis advisors Wiegner and McDermid and committee member Colbert, who have studied sewage pollution on Hawaiʻi Island and with Tonga on Pohnpei, and McDermid, an expert in seaweed who helped Tonga identify the macroalgal tissue samples. He was awarded his graduate degree posthumously in 2021.
“Since 2020, we’ve been working on and off to complete his manuscript,” says coauthor Professor Wiegner, pleased to report the study was published online Friday, March 28.
Establishing baseline water conditions
Tonga leaves behind an invaluable legacy to his homeland and beyond.
As a 2020 story about his research describes, the findings 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.
Tonga spent two summers while a graduate student, 2018 and 2019, in Micronesia collecting water and macroalgae samples from 31 stations around Pohnpei’s coastline, including both populated and forested 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.
Tonga noted at the time that 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.” Added to the mix is development along coastal areas in Pohnpei, which is increasing and causing more water pollution.
Professor Wiegner explains the study helps establish baseline water conditions, needed with climate change because the water quality could shift dramatically.
“In Pohnpei, like here on the island of Hawaiʻi, a lot of houses use cesspools,” she explains. “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 faculty supervisor of UH Hilo’s Analytical Laboratory at UH Hilo, where Tonga analyzed his collected samples. The lab was a second home for him, where he’d been a student assistant for six of his years at the university.
“Bryan’s research for his M.S. degree was cutting edge,” writes Wiegner in a message dated August 2020 to notify the department of his passing. “He completed the first comprehensive water quality study for Pohnpei. He collected water and algae samples over the last two summers, and worked with many partner agencies in Pohnpei, including Pohnpei Environmental Protection Agency, National Food Safety Laboratory in Pohnpei, the Conservation Society of Pohnpei, and the Natural Resource Conservation Service.” He was also mentoring a student from the College of Micronesia.
Wiegner notes in the message that she and McDermid were working with Tonga just days before he passed away to compile his findings and writings to date; he was about three-fourths of the way done.
“He was so happy to see how much he had accomplished,” notes Wiegner in her message. “He was also preparing for a presentation at Hawaiʻi Conservation Conference to share his findings. He was in a good, happy place!”
Story by Susan Enright, a public information specialist for the Office of the Chancellor and editor of UH Hilo Stories.
