A new sensor has been installed on the submersible. Alvin discovered reactive oxygen species in deep-sea corals for the first time, expanding our understanding of fundamental coral physiology. Corals, like us, breathe in oxygen and eat organic carbon. Corals, like humans, produce reactive oxygen species (ROS) as a byproduct of converting energy and oxygen in the body. ROS are a family of chemical compounds that are naturally produced by cells during cell division, while fighting pathogens, and performing other physiological functions.
However, it was previously unknown whether healthy deep-sea corals produce a type of ROS known as superoxide (O2•-). Superoxide is a highly reactive ROS that influences ocean ecology, organism physiology, and driving chemistry in the ocean, including carbon breakdown and metal and nutrient bioavailability.
A new study published in PNAS Nexus reveals for the first time that deep-sea corals and sponges do produce ROS superoxide, implying that these chemicals have a slew of previously unknown effects on deep-sea life and chemistry. The authors demonstrate that ROS are not only produced as a stress response, but are also an essential part of the cell’s functioning.
In the last decade, especially, there have been numerous studies starting to pinpoint how the production of extracellular ROS like superoxide can have beneficial facets to an organism.
Lina Taenzer
In the study, authors took direct measurements of superoxide in water closely surrounding corals, by bringing a one-of-a-kind deep-sea chemiluminescent sensor called SOLARIS, into the ocean over 2,000 meters deep, on board the Alvin submersible.
“These are the first measurements ever of this chemical in the deep sea,” said Colleen Hansel, senior scientist, Marine Chemistry and Geochemistry, at the Woods Hole Oceanographic Institution (WHOI) and senior author of the study.
Detecting superoxide in the ocean is a uniquely difficult task that required collaboration from chemistry to physics to engineering. Superoxide, as a highly reactive compound, only lasts seconds in water. The SOLARIS system was developed by WHOI Engineers Jason Kapit, a co-author on the paper, and William Pardis, along with Hansel and Associate Scientist Scott Wankel, as a robotically controlled instrument capable of pulling in water right at the surface of coral. Water enters the detection wand and mixes within a chamber, where a chemical reaction with superoxide produces light that can be measured in real time. During this expedition, the movements of the wand were controlled with the mechanical arms of Alvin, with Kapit and Hansel part of the three-person team diving inside Alvin.
“One fantastic aspect of this project in particular is that it combines science and engineering in a way that is unique to WHOI,” Kapit said.
The first dives with SOLARIS took place in October 2019 in the Monterey Bay National Marine Sanctuary off the coast of California, where they found large, healthy corals living in a protected ocean environment. This helped eliminate the possibility that superoxide was being produced solely as a stress response.
According to Hansel, the corals they measured were producing superoxide with an enzyme called NOX, which converts oxygen to superoxide outside the cells, implying that it’s most likely a regular part of their life functions – whether it’s growing or possibly producing it to stun prey. Deep-sea corals in their study do not have algal symbionts like shallow corals, which are already known to produce extracellular ROS, which has long been assumed to be derived from symbiotic algae.
These findings rule out algae as a source of superoxide and instead point to the coral animal or its bacterial symbionts. Without additional research, the authors can’t completely rule out bacteria playing a role in ROS production, but they believe it’s unlikely given the presence of NOX in the corals studied here.
“In the last decade, especially, there have been numerous studies starting to pinpoint how the production of extracellular ROS like superoxide can have beneficial facets to an organism,” said Lina Taenzer, Joint Program Student, Marine Chemistry & Geochemistry, and lead author on the study, who joined Hansel’s lab at WHOI in 2019. She also brought Alvin in to use SOLARIS to measure superoxide.
“It is fascinating is that corals can regulate ROS in order to signal to other cells and change how they function and respond to the environment,” Taenzer said. “It’s also interesting in terms of having a cellular defense mechanism.” For example, if an organism is under the invasion of a pathogen, they may produce a strong oxidative burst. This acts as a kind of chemical warfare to protect themselves. On the flip side, over production of superoxide can have detrimental effects on an animal, and can degrade essential proteins in the body and break down DNA.
Species diversity was also important. During her dive in Alvin, Taenzer measured a variety of species by opportunistic chance, including sponges and sea stars.
“There was an aspect of exploration, and the fact that we were using a new instrument we’d never used before that made it really exciting and gratifying,” Taenzer said.
While much remains unknown about how deep-sea corals function and respond to their environment, this study sheds light on the fundamental controls that govern coral health and activity. And the more scientists learn and share, the better they will be able to predict how coral ecosystems will respond to warming seas and climate change.
“It’s difficult to model how corals will respond to changing ocean conditions, if we don’t understand how they currently function under a baseline condition,” says Hansel. “We need to understand what a healthy coral looks like, what a sick coral looks like, and what are some of the factors controlling the health and physiology of these organisms.”
Long-term goals include using SOLARIS to measure coral, deep-sea sponges, and other ROS-producing organisms in other parts of the world to gain a better understanding of how marine life influences ocean chemistry.
“The discovery of these highly reactive compounds in the deep ocean, to name a few, could have an impact on carbon cycling, metal cycling, and microbial ecology. At this point, it’s a complete unknown, but it’s exciting to think about on a larger scale,” Hansel said.
