Climate change is reshaping marine ecosystems in the Northeast Atlantic. Climate change is disrupting the productivity of marine ecosystems across the Northeast U.S. Continental Shelf, according to a new study from the University of Plymouth. The summertime availability of nutrients has dwindled over the last six decades, contributing to a 50 percent decline in large plankton.
Forming the base of the marine food chain, plankton are critical in supporting fish, mammals, and seabirds. Large plankton are being rapidly replaced by much smaller types of plankton as temperatures rise, and the extent of the potential damage is not entirely understood.
“The increasing dominance of small phytoplankton species might have a broad impact on the marine ecosystem. Other than altering the food chain as suggested in this study, it could also change the biological carbon pump modifying the capacity of the ocean to store carbon,” explained study co-author Dr. Luca Polimene.
“We need to make sure that the shift between large to small phytoplankton species is well captured by marine ecosystem models if we want to reliably simulate future oceans.”
Cloudy and wet summers are now being replaced by longer periods of sunshine and drought in the Northeast Atlantic, which is diminishing the iron and nutrient supply in surface waters. This puts a strain on nutrient availability for zooplankton during a time when they need energy the most.
In some regions, large phytoplankton have almost completely vanished while less nutritious picoplankton take over. The tiny picoplankton are not a good source of important dietary supplements, such as Omega-3, and cannot support the continental shelf food web.
One type of picoplankton, the cyanobacterium Synechococcus, is particularly prevalent in the absence of larger plankton. This is because Synechococcus thrives in surface waters when iron and nitrogen levels are low.
According to the study authors, Synechococcus is now dominant in marine ecosystems from the tropics to the Arctic, and its abundance is increasing worldwide. The experts believe that competition for scarce summer nutrients will become a key factor in the structure of shelf food webs.
Around 80 percent of all wild-caught seafood originates in the shallower waters on continental shelves. Declining productivity in these marine ecosystems will have a major effect on the quality and amount of seafood available for humans.
Study lead author Dr. Katrin Schmidt is a plankton ecologist in the University of Plymouth’s School of Geography, Earth and Environmental Sciences.
“Zooplankton such as copepods are considered beacons of climate change, and the 50% decline in their abundance over the last six decades is worrying,” said Dr. Schmidt.
“Our study is the first to provide a mechanism for such a wide-spread decline, and this understanding is essential to project future responses to climate change.”
“We also need to explore the wider impacts and whether the changing nutrient supply could, for example, lead to reductions in omega-3 within the entire food chain.”
The study is published in the journal Global Change Biology.
By Chrissy Sexton, Earth.com Staff Writer