Ocean Food Chains May Be Disrupted

As on land, life in the ocean starts with the Sun. Sunlight nourishes microscopic plants called phytoplankton, which are eaten by tiny animals called zooplankton. Still larger animals feed on the zooplankton. Then these are eaten and on it goes all the way up the "food chain" to large ocean animals. But climate change could disrupt these critical chains by altering the ocean environment: warming and acidifying ocean waters may affect organisms in different ways and to different degrees, throwing closely timed food chains out of sync

Calcareous phytoplankton. This small algal organism, found in marine environments worldwide, is surrounded by a skeleton of calcium carbonate plates that separate and sink to the ocean floor when the organism dies. These plates can make up the major component of a particular rock, such as the chalk of England.

Steve Gschmeissner / Photo Researchers, Inc.

Phytoplankton

Tiny phytoplankton called Ceratium tripos appear every year on the ocean's surface in enormous seasonal blooms that feed countless larger organisms. But over the past half-century, Ceratium tripos blooms in the North Atlantic have peaked on average 27 days earlier than before, likely the result of warming ocean waters.

Zooplankton

Zooplankton are small ocean organisms that graze on phytoplankton blooms. Species like this one, called Calanus finmarchicus, time their life cycles so that plenty of food—phytoplankton—is available when their population peaks. Warming ocean waters in the North Atlantic are suspected to have caused many seasonal phytoplankton blooms to occur 20 to 30 days earlier than they used to. But C. finmarchicus hasn't been able to keep up: its population peak has moved up an average of only 11 days—meaning that today C. finmarchicus may have a harder time finding something to eat.

Fish

Changes in the timing of plankton blooms could have a big impact on larger ocean animals, including commercially important fish species. Newly born zooplankton could eventually find themselves without enough phytoplankton to snack on. In turn, declining zooplankton populations would spell trouble for animals like Atlantic herring.