by Jordan Greer
Even those of us who live in cities understand the importance of forest ecosystems. They provide shelter to a vast diversity of animals and plants, generate the oxygen we breathe, and clean the air of the toxic carbon emissions we produce. But we often fail to consider the unseen, powerful forests living within our oceans.
These undersea forests are comprised of kelp, a type of algae. Algae are the world’s unsung heroes, the foundation upon which most aquatic food chains are built. They provide roughly 70 percent of the oxygen in our atmosphere. Among the algae, kelp forests have earned the nickname “blue carbon” for their superpower to remove more than 170 metric tons of the carbon released into the air each year. This function prevents ocean acidification, a process where fossil-fuel carbon collected on the ocean surface decreases the pH of seawater. As seawater pH decreases, crabs develop more slowly, scallop shells soften, and corals weaken. Kelp, with their voracious appetite for carbon, prevent this process by removing the carbon from the surrounding water and instead incorporating it into their tissues, raising the pH of the local seawater.
In seas across the globe, this blue carbon functions much in the same way as forests on land. Densely packed and able to reach heights of over 90 feet, kelp forests provide food, shelter, and protection to many marine organisms. But while their importance in our oceans is well documented, they might still be hiding their best kept secret: microbes.
University of Chicago professor Cathy Pfister and PhD candidate Brooke Weigel recently discovered a wealth of bacteria living on the surface of kelp. Using DNA sequencing, the team was able to determine the specific groups of bacteria that live on the billowing kelp blades. Notably, two families of bacteria named Granulosicoccaceae and Hyphomonadaceae took up the most real-estate. But what do they do?
This is what Weigel aims to find out during her dissertation research. With early career funding from National Geographic, she wants to better understand the relationships between kelp, microbes, and their ocean environment. Already Weigel and Pfister have exciting ideas of what they may discover.
Remember all the carbon the kelp removed from the atmosphere? Well, Weigel found that roughly 20% of that absorbed carbon is released back into the water as dissolved carbohydrates, like sugar. The most prevalent bacteria have been reported to consume sugar for energy and, as Weigel puts it, “if you are a microbe sitting on the slimy surface on the kelp, you’re basically hitching a ride and getting bombarded with free sugar.” But this feeding frenzy may also work to the kelp’s benefit, as the bacteria may be converting essential nitrogen into a form that kelp can more easily absorb, which in turn could fuel kelp growth. So, similar to how soil bacteria help land plants take in nitrogen, these microbes may be crucial for both nutrient cycling and kelp survival.
To support this idea, the Pfister lab, in conjunction with Jessica Mark Welch, has preliminary results that show that a declining kelp population in Puget Sound also has a severely reduced community of bacteria. While they cannot prove the cause yet, they know the water temperature in Puget Sound—much warmer than in the Pacific Ocean—is one of many potential stressors for the kelp and its microbes. Further research can help determine which came first, the unhealthy kelp forest or bacterial loss, and how these observations may be connected.
As global sea temperatures continue to rise, kelp forests are slowly pushing northward. But how warm can an ocean become before it’s too warm everywhere? By investigating the microbiome of kelp forests, we may be able to answer this question and more fully understand the role of microbes in kelp declines. Losing our kelp would mean losing one of the most important forest systems on our planet, one which provides us oxygen, cleans our oceans, and creates homes for countless ocean species.
Photos by Brooke Weigel
Jordan Greer is an Evolutionary Biology graduate student and science communication intern from the University of Chicago