Climate change damages the base of the marine food web

A new study led by Dartmouth College and the Swedish University of Agricultural Sciences has found that the impact of climate change on freshwater systems can lower nutrition and increase toxicity at the base of the marine food web. The scientists used controlled outdoor environments known as mesocosms in order to study the effects of warming water temperatures and water discoloration caused by increased dissolved organic matter (“browning”). 

“Climate change scenarios predict increases in temperature and organic matter supply from land to water,” said study lead author Pianpian Wu, a postdoctoral fellow at Dartmouth. “For the first time, we used manipulated mesocosm systems to test the effects of warming and browning.”

Dr. Wu and his colleagues used 24 thermally insulated plastic cylinders to assess the effects of different levels of warming and browning under four different scenarios. These mesocosms were controlled at subalpine conditions, which are highly prone to climate change effects and poor in dissolved organic matter.

“The use of mesocosms to investigate questions related to ecosystem effects of climate change is particularly important,” explained study co-author Celia Chen, a research professor at Dartmouth. “The effects of factors such as temperature and browning can be tested individually and in combination while controlling other environmental conditions. Mesocosms also eliminate the need to travel long distances for field investigations.”

Under the expected scenario of increased warming, changing precipitation patterns, and higher levels of disintegrated organic matter, the researchers found that a combination of warmer, browner water led to higher transfer of methylmercury (a potent neurotoxin easily absorbed by marine organisms) from water to the phytoplankton at the base of the food web. 

Furthermore, such conditions gave rise to lower concentrations of essential polyunsaturated fatty acids, such as omega-3 and omega-6, which support the growth of animal and plant life by regulating immune systems and providing energy.

“The reduction of polyunsaturated acids at the end of the mesocosm experiment with both warming and browning effects was concerning,” said Dr. Wu. 

“This study shows that the food quality at the base of aquatic food webs deteriorates with climate change,” added study senior author Kevin Bishop, a professor at the Swedish University of Agricultural Sciences. “The research is important because it places food web investigations within the context of active global change processes.” 

The study is published in the journal Nature Scientific Reports. 

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By Andrei Ionescu, Earth.com Staff Writer