Tiny marine algae, known as phytoplankton, are the backbone of the marine food chain, yet a new study in Nature has found that this backbone is disintegrating. Researchers discovered that since 1950 phytoplankton has declined by approximately 40 percent across the Northern Hemisphere, a decline that corresponds to warming waters due to climate change. Given that these microscopic plants feed the oceans’ abundance all the way up the food chain—from zooplankton to fish to seabird to sharks to humans—the decline has likely impacted the very structure of the ocean.

“Phytoplankton are a critical part of our planetary life support system. They produce half of the oxygen we breathe, draw down surface CO2, and ultimately support all of our fisheries. An ocean with less phytoplankton will function differently, and this has to be accounted for in our management efforts,” explains co-author and associate professor, Boris Worm, from Dalhousie University.

Employing both historical records and contemporary data, researchers were able to compile a database with half a million observations in order to recreate the oceans’ phytoplankton populations going all the way back to 1899. In doing so they discovered a continuing decline of around 1 percent of the global average every year. Since the declines were linked to rising temperatures, researchers say that warmer oceans restrict the abundance of nutrients delivered from the deep to the surface. Since such nutrients are essential for phytoplankton production, less nutrients equals less phytoplankton.

“Climate-driven phytoplankton declines are another important dimension of global change in the oceans, which are already stressed by the effects of fishing and pollution,” explains co-author Marlon Lewis, also from Dalhousie University.

According to a number of prominent marine scientists, the oceans are in full-scale crisis. Climate change is leading to more acidic oceans threatening the world’s coral reefs, the most diverse ecosystem in the oceans. In addition overfishing has decimated many top predators, overturning food chains and emptying ecosystems, while pollution, from plastic to oil, are killing charismatic species, such as sea turtles, sea birds, and marine mammals. Nutrient runoff from agricultural fertilizers and sewage are leading to a dramatic increase in oceanic dead zones, where species are essentially starved of oxygen.

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