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SURFO Special: Scouting out marine plastics on the shores of Guam

Each summer, the University of Rhode Island Graduate School of Oceanography (GSO) hosts undergraduate students from all over the country to participate in oceanographic research. These Summer Undergraduate Research Fellows (SURFOs) have not only been working with GSO scientists, but they also have spent part of their time learning how to communicate this science to the public. Although their research experience was virtual this summer, they still did a fantastic job. Read on to find out what they have been up to, and why they everyone should be as excited as they are about their work.

Ahmyia Cacapit is a senior at the University of Guam, majoring in Biology. Over this summer, she worked with Dr. J.P. Walsh (advisor) and Brandon Sheets (mentor) to study marine plastic pollution on Guam’s beaches. Read below for her work!

Plastic: as ubiquitous as sand

Plastic, known for its versatility and accessibility throughout the world, we can hardly imagine life without it. However, a large portion ends up in our oceans with ~13 million metric tons entering the waters every year (Jambeck et. al, 2015). Plastic causes harm to marine life and threatens food supplies as plastic accumulates through the ocean’s food-chain. Particularly in the Pacific, marine plastic debris are a major problem that many islands face. However, specific distribution around island nations and territories are unknown. On these islands, the coasts serve as sinks for marine plastic by allowing plastic to accumulate on shores through current patterns and human influences (Olivelli, Hardesty, & Wilcox, 2020). Guam, a United States territory in the Western Pacific, is no exception to the problem of marine plastic pollution. These debris affect the island’s industry of tourism and local fishing, posing both a concern to its aesthetic values and fish populations.

Despite an abundance of plastic on the shores of Guam, I had not found any previous study that measured the amount marine plastic found on the island. I saw a need for finding an answer this question: What is the distribution of marine plastic along Guam?

By surveying Guam’s beaches, I wanted to gain a better understanding of where marine plastics accumulate along the island’s coasts. Through this study, I aimed to find where plastic is most prominent and infer the major source of plastic input on the island, either from local sources or off-island transport.

Looking at Litter

I surveyed eight beaches in Guam: three sites on the western coast, four sites on the eastern coast, and one site on the northern coast. I set up three transect lines that passed through three distinct beach zones: the swash zone, high tide line, and backshore. I conducted a visual count of plastic debris by recording items that were visible at eye-level on each transect.

Then, I took photos at each zone within each transect, and plastics in the photo were measured. On the middle transect, I also took plastic samples by digging up 5 cm of sand/sediment and sieving it to see if it contained any plastic particles. I then analyzed the samples using a microscope and classified plastic particles based on size and color.

A site picture of Ritidian Beach on the northern coast of Guam. This picture shows how the transect lines pass through three distinct zones of the beach. This site is a wildlife refuge and receives a relatively small number of visitors throughout the year.

Plastic in Guam

I found that plastic in Guam was highest on the eastern beaches of the island. This is probably due to the wind and current patterns that influence the eastern side of Guam whereas the western side is less impacted by these forces. South Pago Bay had the highest concentration of plastic. When I sampled South Pago Bay, I had noticed that there were different types of debris with Chinese and Japanese writing, possibly indicating that they were transported to Guam from far away offshore sources. Overall, Guam had relatively low plastic concentrations compared to those of other neighboring Asian countries. Hopefully, by identifying how plastic ends up in different areas throughout the island, my study can help the people of Guam know where to focus their efforts for cleanups and park management.


Jambeck JR, Geyer R, Wilcox C, et al. 2015. Plastic waste inputs from land into the ocean. Science 347: 768–71.

Olivelli A, Hardesty BD, Wilcox C, 2020. Coastal margins and backshores represent a major sink for marine debris: insights from a continental-scale. Environmental Research Letters 15: 07403


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