A team of researchers at UC San Diego’s Scripps Institution of Oceanography used a groundbreaking instrument package to assess the chemistry of coral reef environments at a time when scientists are concerned about the effects of increasingly acidic seawater.
Todd Martz, an associate professor of marine chemistry in geosciences at Scripps, led the development of the Benthic Ecosystem and Acidification Measurement System (BEAMS) to measure biochemical variables commonly used to gauge the health of coral reefs. He and other researchers tested the system at the Palmyra Atoll in the northern Line Islands of the central Pacific.
Martz and his team measured variables of interest to researchers including net community production (NCP), or the balance of oxygen and carbon production, and net community calcification (NCC), which assesses the degree of calcification or dissolution of the reef. Automation of these two measurements using BEAMS allows scientists to detect metabolic changes in diverse benthic communities and reef ecosystems in tandem with changes, seasonal or otherwise, in the environment.
Measuring metabolic rates of coral reefs allows scientists to understand the fundamental function of these ecosystems.
“Some people have started calling it ‘taking the pulse’ of coral reefs. The idea and hope is that we can measure these rates to monitor coral reef health,” said Martz’s former student Yuichiro Takeshita, who led a report on the use of the system. “We have just started exploring the potential of BEAMS.”
Corals are among the marine organisms considered especially vulnerable to ocean acidification, a phenomenon attributed to the oceans’ uptake of carbon dioxide produced by human activities in excess of what exists in the atmosphere naturally. Taken in by the ocean at its surface, a portion of the CO2 is converted to carbonic acid. The process also leads to a reduction in the amount of the compounds that corals and shelled organisms need to create their protective structures.
Takeshita, Martz, and colleagues described the use of BEAMS in a recent paper, “Assessment of net community production and calcification of a coral reef using a boundary layer approach,” in the Sept. 21 edition of Journal of Geophysical Research – Oceans.
“This is the first self-sufficient system that can take measurements of NCP and NCC at the same time, under natural conditions, over timescales from a few minutes to two weeks,” said Martz.
Historically, studying changes in water chemistry has been both labor- and time-intensive, with researchers measuring water chemistry over the course of 24 to 48 hours, taking samples at various points throughout that time window—a task that’s hard to maintain for more than a day or two.
“When we try to incorporate the importance of coral reefs into global carbon budgets, we’re basing almost all of our conclusions on one day of measurements that has been extrapolated to a year, which is unreasonable,” said Martz. “You can’t just take a single measurement and multiply it by 365.”
A major advantage of BEAMS is that researchers can maintain an intensive sampling schedule without needing to recover the sensors for several days.
“At this point, we can keep the system out for two weeks,” says Martz. “After we address a few engineering issues, we predict that it could be left out for months.”
Martz largely credits Takeshita for many of the lab’s successes and growing number of collaborations. Takeshita obtained his PhD in Marine Chemistry and Geochemistry at Scripps in 2014, and is now starting a position as an assistant scientist at the Monterey Bay Aquarium Research Institute (MBARI).
“Yuichiro has trained people and has participated in more field deployments of sensors than anyone else,” he said.
The creation and use of BEAMS is exciting for the field, but the use of autonomous chemical sensors in the ocean is something Martz began working on years ago. Now in his eighth year at Scripps, Martz has been a part of numerous exciting collaborations, spanning back to his days in graduate school.
This past year, two ocean sensors that Martz worked on as a graduate student and postdoctoral researcher took first and second place, respectively, for the Wendy Schmidt Ocean Health XPRIZE, a competition that, from a pot of $2 million, awards scientists who create “breakthrough sensors that can help us begin the process of healing our oceans.”
Martz’s postdoctoral advisor at MBARI, Kenneth Johnson, was a leader of the second place team, and was the first to implement use of one of those instruments, the Honeywell Durafet, in the ocean more than a decade ago.
“That’s where everything started,” said Martz.
Martz and his lab have continued to collaborate with Johnson, and recently placed the first pH sensor on a profiling float, an instrument platform in the ocean that alters its buoyancy to collect measurements as it travels up and down in the water.
Most of Martz’s work has focused on the development of new sensors. Now, his lab is shifting toward performing research with these sensors as well. For the research at Palmyra, for instance, he teamed up with Scripps coral reef ecologist Jennifer Smith, who has traveled to the remote island several times to study its ecology.
“It's a really exciting time to be working on autonomous chemical sensor development,” said Takeshita. “Rapid advancements have been made in chemical sensing technology over the past decade or so, which have made them more reliable, accurate, and accessible for the oceanographic community.”
Samantha H. Jones is a fourth-year doctoral student in the Biomedical Sciences program at UC San Diego.