What Forams Tell Us About the Changing Ocean

Visiting scientists leverage Bermuda’s unique ocean setting and long-term datasets to uncover how foraminifera record and respond to ocean change

Foraminifera, or “forams” for short, are single-celled organisms that build shells, or “tests”, often made of calcium carbonate, the same compound found in coral skeletons.

Forams are among the most abundant shelled organisms in many marine environments, with approximately 4,000 species living across the world’s oceans. Of these, only about 10% (40 species) are planktonic, which means they drift in the water column. The rest live amongst the sand, mud, rocks, and plants.

Foraminifera form the basis of multiple marine food chains. Additionally, when they die, their shells fall to the seafloor, helping to form ocean sediment. These organisms are also critical to the geological record, with fossilized forams tracing back more than 500 million years. 

In Bermuda, red foraminifera (Homotrema rubrum) grow on the underside of coral structures. As these forams die and sink, their tests mix with crushed skeletons and natural materials to form the pink color iconic to some of Bermuda’s beaches. 

Bermuda’s unique location in the Sargasso Sea makes it ideal for studying foraminifera, and the island boasts a rich history of foram research dating back to the 1950s. In the following years, Arizona State University Bermuda Institute of Ocean Sciences (ASU BIOS) became central to this work, with multiple foundational studies conducted on-site. Today, forams continue to draw scientists to the station, attracting two international research groups in 2025. 

Collaborating onsite with ASU BIOS oceanographers Amy Maas and Leo Blanco-Bercial, the two teams conducted individual studies on foraminifera, building on Maas and Blanco-Bercial's ongoing plankton research, as well as the extensive documentation provided by the Oceanic Flux Program and Bermuda Atlantic Time-series Study (BATS).

In March of this past year, a group of 11 researchers led by Thomas Chalk, from CEREGE, visited ASU BIOS to investigate how foraminifera shell chemistry responds to changing carbon conditions in the ocean. The multi-institutional research team from CEREGE, Case Western Reserve University, and the University of Southampton conducted additional studies on foram reproduction, feeding habits, and the sensitivity of local sediment to acidification.

“You need to be able to get to open water to collect planktonic forams,” said Chalk. “That’s why Bermuda is so great, because you can access the deep sea super quickly, using a small boat, which is difficult from a large continent. You are also in the middle of an oligotrophic gyre, which was exactly what we wanted for our research.” Oligotrophic means that the waters are very nutrient-poor, which inhibits lots of biological activity, and is perfect if you want to study the ocean water itself. 

The chemistry of forams’ calcium carbonate shells reflects the chemistry of the water in which they grow, meaning that they can be used as a “proxy” for understanding ocean conditions at a specific point in time. Chalk’s group mimicked changing chemical conditions in the laboratory and conducted experiments to determine how these organisms might respond to variations in temperature, pH, and carbon dioxide concentration. They did this by measuring the growth, mortality, and chemical composition of the shells formed during the experiments. 

Planktonic foraminifera also attracted the attention of Laura Haynes from Vassar College and Jennifer Fehrenbacher from Oregon State University, who visited ASU BIOS in July of this past year.

“The level of coordination, support, and training at BIOS makes it great for visiting scientists,” said Haynes. “This was my first time leading a foraminifera culturing season, in a place I hadn't been before. But Amy, Leo, and Roxi made absolutely sure we had what we needed for success, giving us experimental capabilities that I have not had before.”

Bringing a team of seven undergraduate students, the group collected and cultured forams to see how they responded to a proposed climate solution, Ocean Alkalinity Enhancement (OAE). 

OAE involves dumping basic minerals into surface waters to increase the ocean’s overall alkalinity, in an attempt to help the ocean absorb more carbon dioxide. At the same time, OAE may alleviate some of the symptoms of ocean acidification. However, as foraminifera grow, they take up some of these dissolved minerals to make their shells, which has the potential to reduce the efficacy of OAE. 

The team plans to return this summer to further investigate how the proposed sources of alkalinity in OAEs impact foraminifera growth, focusing on factors such as seawater chemistry and mineral types.

“We are so excited to come back,” said Haynes. “We learned a lot about doing these experiments the first summer. And now we can come back and fill in some gaps and try some new experiments to see what would happen.”

Now, at the beginning of a new year, the team at ASU BIOS looks forward to furthering a shared mission of science and innovation through future collaborations and maintained partnerships. Among an exciting suite of upcoming projects, this includes welcoming back visiting scientists and building on Bermuda’s legacy as a hub for research on plankton and foraminifera.