Evolving phytoplankton can tolerate warming waters

Carbon dioxide is a colorless gas that exists in a concentrated form in the atmosphere (330 ppm) and is released into the environment in very high quantities when burned. The current amount of carbon out of fossil fuels is 600 times greater than that into fossil fuels. With the mounting concerns over global warming and the impact carbon dioxide emissions have on the greenhouse effect, scientists have been looking at ways to approach this using a biological process.

Phytoplankton are microscopic water plants found in both fresh and salt water environments. Worldwide, these small organisms can absorb greater amounts of atmospheric carbon dioxide compared to rainforests. A study conducted by the University of Exeter in Cornwall, England, found that phytoplankton exposed to warming temperatures modeling those expected at the end of the century initially failed to thrive. However, at the end of 45 days (approximately 100 generations) the populations showed an evolving tolerance for the increased temperature. The experiment also showed that as the water temperature rose, the phytoplankton were able to absorb more carbon dioxide compared to the amount of carbon dioxide absorbed at the current water temperature.

"As water temperatures increased, phytoplankton were able to absorb more carbon dioxide."

The research and the results
The researchers used a common phytoplankton species Chlorella vulgaris (typically utilized in climate modeling), and exposed it to temperatures between 20 and 33 degrees Celsius. The organism's population size increased through 30 degrees; however, once the population was exposed to 33 degrees Celsius, the population was stressed, and the growth rate began to slow and decrease. The researchers held the temperature steady at 33 degrees for 100 generations, and during that time, the growth rate increased exponentially showing that the species evolved from exposure to the warm conditions.

The mechanism that allows this species to tolerate warmer temperatures was an rise in the effectiveness in which the Chlorella vulgaris was able to convert carbon dioxide into new biomass by reducing the amount of CO2 produced during cellular respiration. This shift in the rates of photosynthesis and cellular respiration has allowed this species and others to cope with the warming aquatic temperatures around the world.

"Our results demonstrate that evolutionary responses of phytoplankton to warming should be taken into account when developing models of how climate change will affect aquatic ecosystems," said a member from the research team at the University of Exeter Penryn Campus. "This experimental work provides the empirical basis for incorporating evolution into the models used to forecast future ocean productivity."

Overall, the results indicate that aquatic ecosystems may be able to sustain the warming temperature.

"Our findings suggest that evolution could play a key role in shaping how aquatic ecosystems respond to climate change," Dan Padfield, a PhD student at the Environment and Sustainability Institute at the University of Exeter's Penryn Campus, explained. "The phytoplankton in our study adapted to warmer water in the lab and evolved the ability to capture more atmospheric carbon dioxide."

Warming waters can have a direct correlation with phytoplankton's ability to survive.Warming waters can have a direct correlation with phytoplankton's ability to survive.

The potential negative impact of evolving phytoplankton on the world
Eutrophication is a natural process occurring in waters that have high concentrations of nutrients, including phosphorus and nitrogen, which promote the growth of algae, according to the U.S. Department of the Interior. Once the algae die and break down, high levels of organic matter as well as the increased nutrients deplete the water of oxygen, causing the other organisms in these ecosystems to die. Human activity has accelerated the speed at which eutrophication occurs, especially in areas with a high amount of industrial plant runoff. The rise in temperatures due to global warming has already impacted the expansion of phytoplankton populations, which can cause a multitude of problems for water supply. Increasing phytoplankton populations can lead to algae blooms and the degradation of aquatic ecosystems in eutrophic bodies of water.

Eutrophication can also destroy aquatic ecosystems and greatly impact any organisms that live directly or indirectly on these aquatic organisms. Increasing levels of algae and other microorganisms can stimulate the productions of toxins in the water supply as well how it is passed through trophic levels. To prevent public health concerns, coastal communities need to have water quality consultants and assessments to test for different toxins as well as other microorganisms.

"Climatologists have been using phytoplankton to reassess their models of the carbon cycle."

The potential positive impact of evolving phytoplankton on the world
Climatologists have been using phytoplankton to reassess their models of the carbon cycle and the impact carbon dioxide will have on the planet. Phytoplankton have recently been reevaluated in terms of their effect on climate models and how productive they are in moving carbon through the biosphere. According to an article published in the Proceedings of the National Academy of Sciences (PNAS) in 2015, the geophysical impact of phytoplankton can greatly alter the projections of climate models currently being used to predict global warming. In Arctic Ocean waters, a fully coupled ocean atmosphere model that interacts with a marine ecosystem model reveals that the future of phytoplankton can and has influenced the greenhouse gasses being circulated in biogeochemical cycles.

The rise in temperature has caused Arctic ice to melt, prompting a rise in the population of phytoplankton. The phytoplankton growing season has also lengthened, causing a thicker layer of algae on the surface water, which is increasing the water temperature. This is causing an even more intense melting of Arctic ice, which has led to desalination, water current changes and more algae blooms. The role of marine organisms impacting climate modeling is valuable in assessing how the greenhouse gases are being circulated throughout the globe. Many of these phytoplankton organisms have the potential for decreasing or balancing the carbon dioxide in the atmosphere by carrying the carbon with them into the body of water as they die and decompose. Further research is looking at the impact of expanding phytoplankton in aquatic ecosystems as well as how both could positively and negatively impact future climate models.