Zooplankton Research Sheds Light on Future Northern Bering Sea Ecosystem

Zooplankton are a diverse community of animals and a critical link in the Bering Sea food web. Image: NOAA Fisheries.

New NOAA Fisheries research exploring the impact of unprecedented losses of sea ice on the northern Bering Sea ecosystem has identified a decline in high-fat copepods that are an important food source for many predators, and expansion of smaller zooplankton with warming waters.

From fish to whales, nearly every predator in the sea eats zooplankton or eats something that does, notes the study led by research oceanographer David G. Kimmel, with NOAA’s Alaska Fisheries Science Center in Seattle.

The study concludes that this altered prey field may have contributed to ecosystem-wide impacts on fish, seabirds and marine mammals. The shift to smaller, more nearshore zooplankton may have contributed to dramatic impacts on commercially harvested fish, protected seabirds and marine mammals in recent years, the report said.

Previous studies have shown that a smaller zooplankton prey field means less energy reaches predators higher in the food web. Smaller zooplankton tend to be less nutritious, both in terms of total energy and fat content. Also there are likely more food chain links between small prey and higher predators— and energy is lost on each link.

“The northern Bering Sea is on the front line of climate change,” Kimmel said.

“In the study of ecosystems you rarely see large-scale changes this rapid and dramatic,” he added. “We need to increase our monitoring to be able to predict change, so people won’t be completely surprised by an ecosystem that is not going to behave as it has in the past.”

The word “plankton” comes from the Greek for “drifter” or “wanderer.” An organism is considered plankton if it is carried by tides and currents and cannot swim well enough to move against these forces.

Some plankton drift this way for their entire life cycle. Others are only classified as plankton when they’re young, but they eventually grow large enough to swim against the currents. Plankton are usually microscopic, often less than one inch in length, but they also include larger species like some crustaceans and jellyfish.

Plankton is composed of the phytoplankton (the plants of the sea) and zooplankton (zoh-plankton) which are typically the tiny animals found near the surface in aquatic environments. Like phytoplankton, zooplankton are usually weak swimmers and usually just drift along with the currents.

Phytoplankton are microscopic plants, but they play a huge role in the marine food web. Like plants on land, phytoplankton perform photosynthesis to convert the sun’s rays into energy to support them, and they take in carbon dioxide and produce oxygen.

Because they need the sun’s energy, phytoplankton are found near the water’s surface. Zooplankton include microscopic animals (krill, sea snails, pelagic worms, etc.), the young of larger invertebrates and fish, and weak swimmers like jellyfish.

Most zooplankton eat phytoplankton, and most are, in turn, eaten by larger animals, or by each other. Krill may be the most well-known type of zooplankton; they are a major component of the diet of humpback, right, and blue whales.

During daylight hours, zooplankton generally drift in deeper waters to avoid predators, but at night, these microscopic creatures venture up to the surface to feed on phytoplankton. This process is considered the largest migration on Earth; so many animals make this journey that it can be observed from space.

The study findings are expected to inform sustainable ecosystem-based fisheries management of Alaska’s valuable marine resources in the face of climate change.