About This Species
Phytoplankton are tiny—almost microscopic—but don't let that fool you. These free-floating, plant-like organisms occupy the bottom of the ocean's food chain, making them vital to the ecosystem. They live in the ocean and in sea ice, and like plants on land, phytoplankton need sunlight. Most are buoyant and float in the upper portion of the ocean where sunlight can reach them. They provide food for a wide array of species, like whales, shrimp, snails and jellyfish.
In the Arctic, phytoplankton blooms are triggered by the melting of sea ice in spring. Light green shelves of phytoplankton swirl into the Arctic Ocean. As the climate changes and the oceans warm, the timing of phytoplankton blooms is shifting and the species are showing up in different places altogether. As this happens, the effects ripple outward, growing in significance along the way.
Warmer oceans are already resulting in earlier blooms. A new study in the journal Science found that for every degree that the water increased, one species of phytoplankton bloomed four or five days earlier. From 2003 to 2012, the bloom of that one species shifted 20 days earlier—a trend the researchers projected would continue as the oceans warm further.
This is important for a few reasons.
Many species tie their lifecycles to the timing of the bloom. When phytoplankton blooms earlier, the next level of the food chain—zooplankton—can miss its opportunity to feed on phytoplankton. That mismatch can work its way up to the fish that eat the zooplankton, the seals that eat those fish and the polar bears at the top of the food chain.
In addition, when thick, old sea ice is thinned by warming, sunlight is able to permeate the surface and stimulate phytoplankton to bloom within the ice. What was once a white surface is made dark, which absorbs more energy from the sun and exacerbates warming.
A combination of ocean warming and shifts in ocean circulation and surface conditions has phytoplankton on the move. In the coming century, species will shift northeastward, with major consequences for the ecosystem.
That northeastward shift is happening at a faster rate than previously estimated. A study published in March 2015 in the Proceedings of the National Academy of Sciences described the dynamic combination of rising ocean temperatures and changes in ocean circulation and surface conditions that are driving this shift.
The study examined 87 North American phytoplankton species, looking at historical data from 1951-2000 and projections for 2051-2100. It found that 74 percent of the species it studied were moving toward the North Pole at a rate of 8 miles per decade, and that 90 percent were shifting eastward at a rate of 26.5 miles per decade.
"Anthropogenic climate change over the coming century may drive North Atlantic phytoplankton species ranges and communities to move in space, or shift, and cause communities to internally reassemble, or shuffle," the study says.