Different types of marine phytoplankton respond differently to warming ocean temperatures – URI News

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NARRAGANSETT, RI – November 17, 2021 – Tiny marine plants called phytoplankton are the basis of most food webs in the ocean, and their productivity drives commercial fishing, carbon sequestration and healthy marine ecosystems. But little is known about how they will respond to rising ocean temperatures resulting from climate change. Most climate models assume that they will all react the same.

But a team of researchers at the University of Rhode Island’s Graduate School of Oceanography, led by former doctoral student Stephanie Anderson, concluded that different types of phytoplankton will respond differently. An examination of how four key groups of phytoplankton will respond to forecast ocean temperatures between 2080 and 2100 suggests that their growth rates and distribution patterns are likely to be different, which will have important implications for the future makeup of the world’s marine communities. whole.

“Phytoplankton are among the most diverse organisms on Earth, and they fix about as much carbon as all the land plants in the world put together,” said Anderson, now a postdoctoral researcher at the Massachusetts Institute of Technology. “Every other breath you take is generated by phytoplankton. And which ones are present affect which fish can be taken care of in a given region.

Anderson, URI Professor of oceanography Tatiana Rynearson and her colleagues at MIT, the Scripps Institute of Oceanography, and Old Dominion University published the results of their research in the Nov. 5 issue of the journal. Nature Communication.

“This study represents a key contribution to understanding how phytoplankton respond to warming oceans,” said Rynearson. “All predictions of climate change in marine ecosystems include a term that reflects how we think phytoplankton growth responds to temperature. In this study, we generated new, more precise values ​​for the temperature-growth response that better reflect the diversity of phytoplankton in the ocean. These new values ​​can be used in future climate change forecasts, helping them to become more accurate. “

The researchers compiled temperature-related growth measurements from more than 80 existing research studies on four types of phytoplankton – diatoms, which thrive in nutrient-rich regions; cyanobacteria, which dominate in the high seas where nutrients are low; coccolithophores, which are particularly important in carbon uptake; and dinoflagellates, which migrate vertically in the water column. They also looked at each group’s heat tolerance and performed a simulation of projected temperatures to determine how the distribution and growth rates of phytoplankton would change in different parts of the world.

They found that each group has a different tolerance to warming.

“Coccolithophores will likely experience the greatest proportional growth decreases near the equator, which could potentially change the makeup of the community there,” Anderson said. “Cyanobacteria, on the other hand, are expected to face the largest proportional growth increases at mid-latitudes, and they could extend their range towards the poles. “

“We were surprised that our simulations predicted the greatest range change for cyanobacteria in the Gulf of Alaska and the northeastern Pacific Ocean, areas that support rich and abundant fisheries,” he said. added Rynearson. “It is important to note that cyanobacteria are not known to be very good food for fish. “

The researchers said the four groups of phytoplankton are expected to increase their growth rate in colder regions, but the degree of increase varies by group.

“With all of the groups, we would expect their growth rates to decline closer to the equator,” Anderson said. “The equator is already the hottest region, so rising temperatures could push them to their limits. Temperatures there will exceed levels they are comfortable with, hampering their growth.

Most species can tolerate temperatures higher than those they typically face, the researchers said, but the margin between what they typically face and the level at which they cannot survive shrinks as they get closer. from the equator.

“There is a lot of capacity to deal with polar warming, but that capacity decreases at the equator,” Anderson said.

The research team also found that dinoflagellates had the smallest change in growth rate in response to the increase in temperature of any of the groups examined, and that they tolerated the widest range of temperatures.

“Their metabolic rates aren’t as likely to be affected by temperature changes as the other groups,” Anderson said. “We hypothesize that this could be due to the fact that they are vertical migrants. Their ability to swim up and down exposes them to more temperatures, potentially allowing them to handle more temperature changes. “

The implications of these results are significant. At the equator, where phytoplankton growth rates are expected to decline as temperatures rise, the reduced phytoplankton biomass can support fewer fish and other marine organisms.

“If you are a fish and depend on one type of food and it is no longer present, you may have to move with your prey to survive,” Anderson said. “This could lead to changes in food webs at the regional level. “

At higher latitudes where growth rates are expected to increase, the higher biomass of phytoplankton may be able to support more fish, thereby boosting commercial fisheries.

The study did not take into account other factors that may affect phytoplankton growth rates, such as the availability of nutrients or light. Anderson therefore said the implications of the study are somewhat speculative. She is now incorporating these additional factors into a new model to see how the results may change.

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