UH Hilo alumnus leads study on impact of sewage on coral reefs in Puakō; published findings show the pollution likely contributes to algae cover

The study sought to determine if the sewage from the homes in Puakō, Hawai‘i Island, was reaching the nearshore coral reef and potentially contributing to the deteriorating reef health condition.

Diver collects data from coral reef.
UH Hilo alumnus Devon Aguiar, lead author of a recently published study on sewage pollution impacts on coral reefs, conducts a benthic survey at Puakō, Hawai‘i Island. (Courtesy photo)

By Susan Enright.

A study published this month conducted by marine scientists from the University of Hawai‘i at Hilo and other colleagues shows the presence and impact of sewage on the coral reefs of South Kohala, namely Puakō, on Hawai‘i Island.

Lead scientist of the study (“Detection and impact of sewage pollution on South Kohala’s coral reefs, Hawai‘i,” Marine Pollution Bulletin, Volume 188, March 2023), is UH Hilo alumnus Devon Aguiar, who graduated in 2020 with a master of science degree from the tropical conservation and environmental science program. Aguiar is currently a fish and habitat monitoring specialist for the Hawai‘i Division of Aquatic Resources.

“In addition to describing the impacts of sewage pollution in South Kohala, our study also emphasized the use of multiple research methods,” says Aguiar. “Drawing from the disciplines of ecology, microbiology, and oceanography, we were able to provide an enhanced perspective on reef and benthic water conditions in South Kohala. It is my hope that these results can support efforts to reduce anthropogenic nutrient inputs on reefs within and outside of Hawai‘i.”

Co-author of the study Tracy Wiegner, a professor of marine science at UH Hilo who is an expert in sewage pollution in marine environments, mentored Aguiar through several water pollution studies while he was a student.

Other co-authors of the study are UH Hilo marine scientists Steven Colbert, John Burns, and James Beets; Leilani Abaya and Jazmine Panelo who also graduated from the UH Hilo master’s program; and Julia Stewart from the marine science department at UH Hilo.

In addition are co-authors Kristina Remple and Craig Nelson from UH Mānoa, and Courtney Couch of the National Oceanic and Atmospheric Administration’s Pacific Islands Fisheries Science Center in Honolulu. The Nature Conservancy also collaborated.

Sewage pollution at Puakō

Pollution from on-site sewage disposal systems and injection wells is impacting coral reefs worldwide. Through onsite testing and reef surveys at Puakō, the researchers found sewage pollution was moderate on the offshore reef from seeps, and that water motion mixed and diluted the pollutant.


Map of Puakō showing where researchers conducted their study along the coastline.
Map above displays the study stations along the South Kohala coastline, Hawaiʻi Island. Stations were assigned into one of five color coded regions (South Resorts, South Puakō, Middle Puakō, North Puakō, North Resorts), based on their proximity to the resorts or the Puakō community. Samples, surveys, and deployments were conducted June 2018 and 2019. (Map is from the published study, used with permission)

Tracy Wiegner
Tracy Wiegner (Raiatea Arcuri)

The authors of the study believe these conditions likely contribute to the dominance of turf algae cover, and the severity and prevalence of growth anomalies and algal overgrowth on corals. The study revealed that water motion was necessary to assess sewage pollution and identify environmental drivers associated with impaired coral health conditions.

Further, the researchers note the methods they used in this study could be utilized by natural resource managers to identify and reduce human-caused problems to coral reefs.

The study was the third this research team conducted at Puakō.

“In 2014, the Puakō community asked us if there was sewage pollution in their nearshore waters,” says Wiegner, an expert in marine pollution who has led multiple studies on offshore waters of both east and west Hawai‘i Island. “Our first project demonstrated that there was. Our second project focused on figuring out where in the Puakō watershed the sewage was coming from.”

UH Hilo researchers partner with Puakō community to improve human and coral reef health

UH Hilo marine scientists identify sources of pollution in coastal waters off West Hawai‘i

The researchers determined that it was largely from the homes in Puakō and that travel time of the sewage from a home to the shoreline was the same regardless of the onsite sewage disposal system (OSDS) type—meaning cesspool, septic tank, or aerobic treatment units—with the underlying geology of the property being more important in determining how fast the sewage reached the shoreline.

Working on solutions with community

This most recent project just published sought to determine if the sewage from the homes in Puakō was reaching the nearshore coral reef and potentially contributing to the deteriorating reef health condition.

“Sewage pollution was moderate on the reefs from the benthic seeps, and water motion mixed and diluted it across the seafloor,” says Wiegner. “These conditions likely contributed to the dominance of turf algae cover, and the severity and prevalence of growth anomalies and algal overgrowth on corals.”


Three researchers sort through cold cards, which are round chunks of plaster,
Researchers working on the Puako sewage project in 2018 sort through clod cards at their land base. Clod cards are chunks of plaster of Paris that are used in measuring relative water flow; set in the ocean for a specified time, the amount of erosion indicates the volume of water flow. The study revealed that water motion was necessary to assess sewage pollution and identify environmental drivers associated with impaired coral health conditions. (Courtesy photo)

The goal of the research with this project and the past ones was to document current water quality and coral reef health conditions at Puakō, with the eye towards the future when onsite sewage disposal systems will be removed, per Hawai‘i State Act 125 (2017).

“The Puakō community is aiming toward building a sewage treatment plant that will treat the sewage to a R-1 reuse quality, which then could be used for irrigation of a firebreak or some other type of crop,” says Wiegner. “The plants in the firebreak would further take up nutrients that would otherwise be discharged into the groundwater and eventually into the ocean.

UH Hilo marine scientists recommend wastewater treatment plant for Puakō

“A [sewage treatment] plant like this will ultimately stop the raw, untreated sewage from OSDS entering into Puakō’s nearshore waters, improve the water quality, and reduce the health risk to recreational water users and the coral reef,” she adds.

“We  look forward to documenting future improvements in water quality and coral reef health conditions at Puakō.”


Story by Susan Enright, a public information specialist for the Office of the Chancellor and editor of UH Hilo Stories. She received her bachelor of arts in English and certificate in women’s studies from UH Hilo.

Share this story