Ecosystems Fisheries-Oceanography Coordinated Investigations EcoFOCI Bering Sea Ice

Bering Sea-Ice Expedition
Research Activities- Zooplankton


Zooplankton are microscopic animals that drift with the ocean’s currents (planktos means wander in Greek). They are very abundant near the ocean’s surface and come in many different sizes (20 microns to 20 mm), forms and colors. Some eat phytoplankton (microscopic algae), others eat smaller zooplankton. In this way they are at the base of the food web, helping to convert the energy produced by plants to food (prey) that can be used by fish, seabirds, and marine mammals. Some animals only spend the larval part of their lives as zooplankton. Examples are the larvae of mollusks, (clams, snails, squid), echinoderms (starfish, sea cucumbers, sea urchins), crustaceans (crabs and lobsters). Animals that only spend part of their lives in the plankton are called meroplankton. Animals that spend their whole lives in the plankton are called holoplankton. Examples are copepods, euphausiids (krill), and some jellyfish.

The copepod Calanus is prevalent in the Bering Sea.

In early spring, the concentration (number per cubic meter) of zooplankton in the Bering Sea depends on the amount of available food and the water temperature. A phytoplankton bloom (rapid increase in phytoplankton concentration) provides zooplankton with the food they need to grow and reproduce. The sea ice that often covers large portions of the southeastern Bering Sea affects both the water temperature and the amount of light penetrating the water. If the ice stays past the middle of March, then the phytoplankton bloom occurs under the ice, in part because the cold temperatures have slowed the growth and reproduction by zooplankton that eat the phytoplankton. In these situations, most of the phytoplankton sinks uneaten to the sea floor where it helps to feed the benthic food web. Flatfish, walrus and grey whales are part of this food web. In places where the ice retreats before the middle of March, the spring phytoplankton bloom is delayed until May or June, in part because the warmer water allows zooplankton to grow, reproduce and exert more grazing pressure on the phytoplankton as conditions became good for their growth and reproduction. When the bloom occurs later, more of the phytoplankton production remains in the water column fueling a food web that supports pelagic fish, seabirds, baleen whales.

During this expedition, scientists will sample zooplankton from beneath ice floes (using SCUBA divers), from the water between ice floes and from open water near, but not part of, the ice edge using nets. Our main goal is to understand how the ice affects the distribution of zooplankton. Another goal is to look for the larvae of snow crab and determine where they are in the water column (what depths). Currents are not uniform with depth, and the location of crab larvae in the water column determines how far and fast they are transported. Our last goal is to measure the rate of reproduction (egg production) by some of the copepods to learn more about how food and temperature affect their reproduction. Analysis of all of these results will provide important information on the food webs of the Bering Sea’s ice-edge ecosystem, and how the loss of sea ice in the Bering might affect the production of animals at higher trophic levels such as fish, seabirds, and marine mammals.

NOAA - National Oceanic and Atmospheric Administration