Reference: Velthuis, M., Keuskamp, Joost. A., Bakker, E. S., Boersma, M., Sommer, U., van Donk, E., & Van de Waal, D. B. (2022). Differential effects of elevated pCO2 and warming on marine phytoplankton stoichiometry. Limnology and Oceanography. https://doi.org/10.1002/lno.12020.
The ocean is becoming hotter and more acidic. While this does not mean the ocean is becoming a pool of acid that will burn you more than the sun when you’re at the beach, it does mean danger for the billions of sea creatures that call the ocean home. This change is due to human fossil fuel use. More fossil fuel burning means more carbon dioxide (CO2), and the ocean is great at absorbing this greenhouse gas. Unfortunately for marine organisms, higher oceanic CO2 absorption leads to a more acidic ocean, which can make it difficult for not only our favorite seafood to make their shells, but for entire food webs to function.
Just like pirates getting scurvy without enough vitamin C, plants can’t function without enough carbon (C), nitrogen (N), and phosphorus (P). In fact, the fertilizers used to grow our food are full of nitrogen and phosphorous to help plants grow faster and healthier. However, we can’t just give plants nutrients and hope for the best, there needs to be a balance, similar to how humans can’t just eat fruit, we need vegetables too. Mother Nature typically keeps the balance between carbon, nitrogen, and phosphorous, but humans are changing the game. We are constantly changing what nutrients are limited in different areas. For example, if an area is nitrogen limited, it means that there is less nitrogen than phosphorus present. In this case, the plants can only grow based on the amount of nitrogen in the area; just like if you are trying to make burgers with 24 sets of buns and 15 patties, you can only make 15 burgers because you ran out of patties. With ocean acidification and other environmental changes, the nutrients available to plants and animals is changing and giving nature its own version of scurvy.
Fight of the Phytoplankton
If trees are the lungs of the land, phytoplankton are the lungs of the ocean, producing about half of the world’s oxygen. While trees have full leaf canopies to collect carbon from the atmosphere and turn it into oxygen, phytoplankton are microscopic and rely on sheer numbers to help transport 9 trillion kilograms of carbon (equivalent to the weight of over 5 million blue whales) from the atmosphere to the depths of the ocean. All 25,000 species of phytoplankton worldwide work together to photosynthesize and create food that is the basis for almost all marine food webs.
Without phytoplankton, the world would be in serious trouble. As humans continue to change the ocean, it is vital to understand how phytoplankton will be affected. So, to understand how phytoplankton will respond to a changing ocean, researchers consolidated 100 scientific studies on phytoplankton and changes in nutrients with ocean acidification and warming. The researchers found that with a more acidic ocean, phytoplankton had a dramatic change in how they used nutrients like becoming more efficient in their use of nitrogen when nitrogen was limited. When the phytoplankton were put under even more stress in nutrient limited conditions, the change was even greater. Essentially, phytoplankton changed the way their cells were functioning due to stress, just like how many people tend to eat more when stressed.
The ocean is warming just like the atmosphere. Each phytoplankton species is used to a different temperature – those in the arctic like it cold, while those in the tropics prefer tank top weather. However, researchers found that most phytoplankton actually grew better with warmer ocean temperatures. Not only does this mean that phytoplankton will grow in size in heat, but it also means that they will be able to reproduce more quickly, creating even more phytoplankton. Scientists think that warmer oceans would make it easier for phytoplankton cells to function and would decrease the amount of phosphorous each plankton needs. Arctic and temperate regions are expected to feel the largest impacts of ocean heating in the future, leading to the largest change in phytoplankton dynamics in these areas.
What this means for the future of climate change
As the climate continues to change, not only will the ocean’s pH and temperature be affected, but nutrient concentrations, salinity, and light availability will vary as well. The ocean is already considered to be a nutrient desert, but it is expected to become more nutrient limited as rising ocean temperatures make it harder for nutrients to circulate. It is expected that decreasing nutrients in the oceans will lower the overall production of the ocean. However, the ability of phytoplankton to change the way their cells function to account for changes in nutrients, ocean temperature, and acidification will help to balance the other losses in ocean production. Phytoplankton are not only the basis for most life in the ocean – without them, all of us living on land would struggle to function and breathe. The ability of phytoplankton to adapt to a world changed by humans will not only help the oceans survive, but will help us in the fight against further climate change by continuing to move carbon from the atmosphere into the oceanic depths.
Featured image from Wikimedia Commons
While I have never lived close to the ocean, it has always had a special place in my heart. I recently earned my PhD in environmental chemistry from the State University of New York College of Environmental Science and Forestry (SUNY ESF) studying reef and coastal biogeochemistry. I focus on the lipid and trace metal composition of settling particles and surface sediment in coastal systems, primarily studying coral reefs. Currently, I am a Visiting Assistant Professor at Trinity College. When not diving or in the lab you can find me hiking with my dogs, reading, cross stitching, or just enjoying a good cup of tea!