The marine plants. Credit:Stephanie Anderson.
The productivity of tiny marine plants called phytoplankton drives commercial fishing, carbon sequestration, and healthy marine ecosystems. They don't know how they will respond to rising ocean temperatures. Most climate models think they will all respond the same way.
A team of researchers at the University of Rhode Island's Graduate School of Oceanography have concluded that different types of phytoplankton will react differently. An examination of how four key groups of phytoplankton will respond to ocean temperatures forecast to occur between 2080 and 2100 suggests that their growth rates and distribution patterns will likely be different, resulting in significant implications for the future composition of marine communities around the globe.
Anderson, who is now a researcher at the Massachusetts Institute of Technology, said that phytoplankton fix roughly as much carbon as all the land plants in the world combined. Every breath you take is generated by the plant. Which ones are present affects which fish can be supported.
The results of their research were published in the journal Nature Communications.
The study is a key contribution to the understanding of how the ocean responds to warming. Climate change forecasts of marine ecosystems include a term that reflects how the growth of the plants responds to temperature. We have generated new, more accurate values for the temperature-growth response that better reflect the diversity of the ocean. Future climate change forecasts can be helped by these new values.
The researchers compiled temperature-related growth measurements from more than 80 existing research studies on four types of phytoplankton, which thrive in high-nutrient regions. They conducted a simulation of projected temperatures to determine how the distribution and growth of phytoplankton would change in different parts of the world.
Each group has a different tolerance for warming.
Anderson said that the coccolithophores will probably face the greatest proportional growth decreases near the equator. The cyanobacteria are expected to face the greatest proportional growth increases at mid-latitudes, and they might expand their range poleward.
"We were surprised that our simulations predicted the greatest range shift for the cyanobacteria in the Gulf of Alaska and northeast Pacific Ocean, regions that support rich and abundant fisheries," said Rynearson. It's known that cyanobacteria are not very good fish food.
The researchers said that the growth rates of all four groups are expected to increase in cooler regions.
Anderson said that they expect growth rates to decrease closer to the equator. The equator is already the warmest region, so increasing temperatures there might push them to their limits. The temperatures there will be too hot, which will affect their growth.
The researchers said that most species can tolerate temperatures greater than those they face, but that the margin between what they face and the level at which they cannot survive decreases closer to the equator.
Anderson said that there's a lot of capacity to handle warming towards the poles, but not at the equator.
The research team found that the dinoflagellates had the smallest change in growth rate when the temperature went up.
Anderson said that the group's metabolism is not likely to be affected by temperature changes. They are vertical migrants, so we think it could be related to that. Their ability to swim up and down exposes them to more temperatures.
The results have significant implications. The reduction in the number of fish and other marine organisms at the equator may be due to the decrease in the growth rates of phytoplankton.
Anderson said that if you're a fish and you're dependent on one type of food, you might have to move with your prey to survive. This could lead to changes in the food web.
The higher the growth rate, the greater the amount of fish that can be supported.
Anderson said the implications of the study are speculative because the study did not consider other factors that might affect growth rates. She is trying to figure out how the results may change.
The Marine phytoplankton functional types exhibit diverse responses to thermal change. There is a DOI of 10.1038/s41467-021-26631-8.
Nature Communications is a journal.
Researchers say different kinds of marine phytoplankton respond differently to warming ocean temperatures.
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