Imagine a car heading toward a cliff’s edge with its gas pedal stuck to the floor. That, Robert Perkins wrote, is a metaphor for “what climate change will do to the key group of ocean bacteria known as Trichodesmium,” according to a study published in the September 2015 issue of Nature Communications by researchers at the University of Southern California and Woods Hole Oceanographic Institution.
Trichodesmium is found in nutrient-poor parts of the ocean, where it converts nitrogen gas into material that can be used by other forms of life. From algae to whales, all life needs nitrogen to grow. Reporting for the Guardian, Emma Howard quoted Eric Webb, one of the study’s researchers, who explained how the process of “nitrogen fixation” makes Trichodesmium “the fertilising agent of the open ocean.”
The study tested the effects of elevated levels of carbon dioxide by subjecting hundreds of generations of Trichodesmium bred over a five-year period to CO2 levels predicted for the year 2100 by the Intergovernmental Panel on Climate Change. Responding to increased ocean acidification, the bacteria went into “reproductive overdrive,” Howard reported, evolving to grow faster and to produce 50 percent more nitrogen. One consequence of this is that Trichodesmium could consume significant quantities of nutrients that are in limited supply in the ocean, such as iron and phosphorous, leaving other organisms that depend on the same nutrients without enough to survive. Alternatively, Trichodesmium might consume nutrients at a rate that would lead to its own extinction, leaving other organisms without the nitrogen that the bacteria makes available. Either way, the effects of elevated CO2 levels on the bacteria could trigger catastrophic effects up the marine food chain.
Most significantly, the researchers found that even when the bacteria was returned to lower, present-day levels of carbon dioxide, Trichodesmium remained “stuck in the fast lane,” a finding that Webb described as “unprecedented in evolutionary biology.” The study’s lead author, David Hutchins, observed, “Losing the ability to regulate your growth rate is not a healthy thing … The last thing you want is to be stuck with these high growth rates when there aren’t enough nutrients to go around. It’s a losing strategy in the struggle to survive.”
The next stages of the team’s research involve studying the DNA of Trichodesmium to better understand “how and why the irreversible evolution occurs,” Perkins reported.
Robert Perkins, “Climate Change Will Irreversibly Force Key Ocean Bacteria into Overdrive,” USC News (University of Southern California), September 1, 2015, https://news.usc.edu/85742/climate-change-will-irreversibly-force-key-ocean-bacteria-into-overdrive/.
Emma Howard, “Climate Change Will Alter Ocean Bacteria Crucial to Food Chain—Study,” Guardian, September 2, 2015, http://www.theguardian.com/environment/2015/sep/02/climate-change-will-alter-ocean-micro-organisms-crucial-to-food-chain-say-scientists.
Student Researcher: Ally Spero (Sonoma State University)
Faculty Evaluator: Carmen Works (Sonoma State University)