The effects of global climate change are already causing loss of sea ice, accelerated sea level rise and longer and more intense heat waves, among other threats.
Today, the first-ever survey of planktonic lipids in the global ocean predicts a temperature-related decrease in the production of omega-3 essential fatty acids, an important subset of lipid molecules.
An important implication of the survey is that as global warming progresses, there will be less and less omega-3 fatty acids produced by plankton at the base of the food web, which will mean less fatty acids omega-3 fats available for fish and for humans. . Omega-3 fatty acid is an essential fat that the human body cannot produce on its own and is widely considered a “good” fat that links seafood consumption to heart health.
The survey analyzed 930 lipid samples from across the global ocean using a uniform analytical workflow of high-resolution, precise mass spectrometry, “revealing previously unknown characteristics of oceanic planktonic lipidomes”, which is the entirety of hundreds to thousands of lipid species in a sample, according to a new paper led by authors from the Woods Hole Oceanographic Institution (WHOI).
“By focusing on ten classes of molecularly diverse glycerolipids, we identified 1,151 distinct lipid species, finding that fatty acid unsaturation (i.e. the number of carbon-carbon double bonds) is fundamentally limited by temperature.We expect significant decreases in eicosapentaenoic acid, an essential fatty acid [EPA] over the next century, which are likely to have severe deleterious effects on economically critical fisheries,” states the paper, “Global Ocean Lipidomes Show Universal Relationship Between Temperature and Lipid Unsaturation,” published in Science.
EPA is one of the most nutritious omega-3 fatty acids, has been linked to numerous health benefits, and is widely available as a dietary supplement. “Lipids in the ocean affect your life,” says review article co-author Benjamin Van Mooy, a senior researcher in the Department of Marine Chemistry and Geochemistry at OMSI. “We found that the composition of lipids in the ocean will change as the ocean warms. This is a cause for concern. We need those lipids that are in the ocean because they influence the quality food that the ocean produces for humanity.
“All organisms in the ocean have to deal with water temperature. With this study, we have revealed one of the important biochemical means that cells use,” says the lead author of the journal article. Henry C. Holm, PhD student at Massachusetts Institute of Technology (MIT) — OMSI Joint Program in Oceanography/Applied Ocean Science and Engineering. “These EPA findings were made possible using a method that gives us a very complete picture of the glycerolipids in each sample. We saw that temperature was related to the saturation of cell membranes everywhere we looked in the ocean. .”
Lipids are a class of biomolecules produced and used by organisms in all domains of life for energy storage, membrane structure, and signaling. They represent about 10 to 20% of the plankton at the surface of the ocean, where the production and the stocks of lipids are the highest. Oceanographers have used lipids as biomarkers of chemical and biological processes for decades, and extensive research has been conducted on their biogeochemistry. It is only recently, however, that the combination of high-resolution mass spectrometry and downstream analytical tools has enabled comprehensive unfocused assessments of ocean lipids at scales similar to investigations of other molecules such as nucleic acids and proteins.
In this new investigation, the researchers examined a global-scale mass spectral dataset of planktonic lipidomes from 146 locations collected during seven oceanographic research cruises from 2013 to 2018. The researchers note that although the lipidomes of the planktonic community are affected by many environmental factors such as nutrient availability, the article reports “the relationship between lipids and arguably the most fundamental control of their composition: temperature”.
The researchers examined the saturation state of the 10 main classes of lipids with glycerol (i.e. glycerolipids) and found that among these classes, “temperature had a great influence on the structuring of the relative abundance of fatty acid species”. Additionally, the researchers found a clear transition from lipid species with more unsaturated fatty acids at colder temperatures to fully saturated species at warmer temperatures.
“These trends are also evident in all other glycerolipid classes as well as in aggregated total lipidomes of all glycerolipid classes,” the paper states. “Indeed, it is striking that the relationship between temperature and unsaturation emerges from our dataset despite such diverse and disparate planktonic communities, from nutrient-depleted subtropical gyres to the highly productive Antarctic coastal shelf.”
The researchers also found that the percent abundance of eicosapentaenoic acid (EPA) species showed a strong relationship with temperature. To determine how the upper and lower bounds of the EPA’s composition might change under future warming conditions, the researchers generated maps using end-of-the-century sea surface temperature conditions for different climate scenarios. Under the SSP5-85 climate scenario, which the article says is considered a worst-case scenario with continued high greenhouse gas emissions, some ocean regions – particularly at higher latitudes – see a drastic decrease of up to -25% in EPA relative to the amount they have now, according to the newspaper.
Van Mooy said the research “is another example of how human activities are disturbing the oceans in ways we didn’t expect, and the uncertainty about how the ocean will react to the Warming”.
This work was supported by grants from the National Science Foundation, the Marine Microbiology Initiative division of the Gordon and Betty Moore Foundation, and the Simons Foundation.