BIOS Deploys New Microsensor Technology in Mangrove and Coral Investigations

Initially drawn to ASU BIOS by the opportunity to drive research into the dynamics of nitric oxide production in corals, Arizona State University PhD candidate Tom Moran arrived in Bermuda in May and was quickly immersed in the Institute’s other work as well. As he prepared to depart in September, Moran was toggling between two separate – but related – interests: the coral thermal stress project led by Assistant Scientist Yvonne Sawall, and research on nitrogen cycling in Bermuda’s mangroves directed by Postdoctoral Scientist Brett Jameson and Assistant Scientist Damian Grundle.

“I’ve enjoyed working in the mangroves. I’m enjoying the marine biogeochemistry and trying to integrate some of that into the coral work as well,” said Moran, who enrolled in ASU’s Environmental Life Sciences Program after earning a Master’s in Oceanography at the UK’s University of Southampton.

With the mangrove field work wrapping up in September and his coral research continuing in ASU’s labs over the winter, Moran said he is “at a bit of a crossroads” about the path his PhD will take. “Going forward,” he mused, “how will I tie in both research themes?”

Climate change and the ability of these marine ecosystems to withstand and adapt to it is a likely common thread.

Coral reefs and mangrove forests might not look the same, but they are alike in the essential environmental benefits they provide to coastal ecosystems and communities. Both not only provide critical habitat for fish and other marine species, but also form protective barriers that shield shorelines from erosion and other physical damage.

Both also share the unfortunate distinction of being among the Earth’s most vulnerable ecosystems and appeals for increased protection have gained more urgency in recent months. In April, amid the fourth global coral bleaching event, a partnership of research and conservation organizations, led by the International Union for Conservation of Nature (IUCN) and including ASU, announced an intensification of efforts to address the “unprecedented threats from climate change, overfishing, and pollution.”

On the heels of that, the IUCN reported in May that over half of the world’s mangrove ecosystems “are at risk of collapse by 2050,” threatened by deforestation, development, pollution and impacts of climate change.

With Jameson, Moran spent the summer working with delicate state-of-the-art microsensors to measure concentrations of trace gases in the sediments of mangroves near the ASU BIOS campus. Besides nitrous oxide (N2O), the project measures levels of sulfide, oxygen and nitric oxide (NO). NO is not itself a greenhouse gas (GHG) but contributes to the formation of ozone, which is a potent GHG when it occurs in the lower atmosphere.

“The nitrogen cycle is very complicated because there are many components to it, and the various processes are performed by highly diverse groups of microbial organisms. Some of these processes contribute to nitrous oxide cycling and that’s what we’re interested in here,” said Moran, noting that N2O’s atmospheric warming potential is roughly 300 times that of carbon dioxide. “We’re basically wanting to come up with a strong argument for why we should protect mangroves. Not only are they really important ecosystems for harboring juvenile fish and providing shelter for many marine life, but also in terms of what they are doing for the climate and the atmosphere.”

To conduct their fieldwork, Moran and Jameson snorkeled to the roots of the local mangrove patch to take sediment cores. Back at the lab, they incubated the cores in aquaria and experimented with adding various levels of nitrate (NO3), a compound found naturally in water but harmful to aquatic ecosystems at high concentrations sometimes caused by agricultural runoff and wastewater discharge. The purpose, Moran said, is to determine “if nitrate levels were to increase substantially, then how would that affect nitrous oxide emissions.”

As of mid-August, the mangrove project hadn’t yet produced conclusive results, but the researchers had done considerable troubleshooting with the microsensors, which Moran called “a bit tricky”. With tips measuring just 100 microns (one-tenth of a millimeter), using them to measure trace gases in the mangrove sediments is intricate work.

Not as intricate, however, as using them to take measurements from coral polyps, the other part of Moran’s research at BIOS.

“The goal of using microsensors on corals is to quantify NO production in corals under heat stress,” said Sawall, adding that it’s “challenging, as the polyps move.” They also have a hard skeleton…and Moran admits having broken a few “dummy” microsensors during initial insertion trials.

“As studies of NO in corals are still scarce and results are highly variable, several questions remain in understanding the role of NO in coral physiology in general and in thermal stress responses in particular,” states the project funding proposal. “We propose to use NO microsensors (along with other more traditional approaches) to advance our knowledge about the role of NO in coral health and bleaching.”

Supported by the Cawthorn Innovation Fund (named for BIOS Trustee Emeritus Rob Cawthorn) and assisted by Canadian Associates of BIOS (CABIOS) intern Claire Hendrikx, this work marks the first time NO microsensor measurements have been conducted on corals and it will define testable hypotheses for a future proposal about coral nutrient cycling and thermal stress response, and the role NO plays in these processes.

“Increased nitric oxide levels have been found in bleached corals as a consequence of heat stress. What I intend to do…is basically to use the NO microsensors to enter the tissue of the coral and see if I can actually measure in situ NO concentrations under different thermal stress conditions,” Moran said. “Basically, can I use this technique applied for the first time here in this setting, and can I use it to deepen our understanding of the role NO production plays in coral thermal stress response.”

Besides not accidentally contacting the coral skeleton and breaking a tip, the main problem has been that coral polyps tend to retract their tentacles when poked with a glass microsensor, wrapping around the instrument and hampering measurements. It’s a difficulty Moran hopes to overcome by numbing them first with magnesium chloride or menthol added to aquaria sea water.

“It’s like an anesthetic for them,” he said. “If you get the coral to relax, it makes it easier to get the sensor into the tissue.”

In terms of next steps, Moran said “if we can get it to work, I will continue with laboratory work in Arizona” with corals in aquaria at ASU during the fall and winter. That time will also be spent analyzing the team’s mangrove data and writing up a manuscript for publication.

Come next spring, pending some visa issues, Moran hopes to be packing his bags again for Bermuda – a place he’s “kind of fallen in love with.”

“For me, being by the ocean, where I do my work, and being able to live and breathe it every day, that’s where I’d like to come back to if I can.”

This research is made possible through support from BIOS Grants-in-Aid and The Samuel Riker Fellowship Fund. We are grateful to our generous donors who have made these GIA funding opportunities possible. Together we are advancing fundamental scientific understanding and we are grateful for the support of our donors.