The copepod and its role in the Arctic food chain
The miniscule copepod Calanus glacialis, a cousin of crayfish and water fleas, influences the diet of many creatures in the Arctic region, particularly during the extreme winter season. A herbivorous Arctic zooplankton species, Calanus successfully adapts to melting sea ice and the blooming of tiny algal species. In a new study, led by the University Centre in Svalbard (UNIS) in Norway, researchers shed new light on the relationship between sunlight, phytoplankton and zooplankton, and how plankton depends on sea ice. The research is part of the CLEOPATRA ('Climate effects on planktonic food quality and trophic transfer in Arctic Marginal Ice Zones') project, an initiative conducted under International Polar Year (IPY), a worldwide research campaign in support of polar science. CLEOPATRA is partially backed by a number of EU projects funded under the EU's Seventh Framework Programme (FP7).
Researchers say this particular zooplankton is probably the most important species of the Arctic region. And algae found either on ice or floating freely in water will be affected by changes made to the ice conditions of the polar continental shelf. Such potential changes could impact Calanus glacialis and its predators.
Melting ice, sunlight and nutrients make the Arctic a fertile hotspot during the summer months, culminating in new life for six months out of the year. And the Arctic food chain is rich in omega-3 fatty acids produced exclusively by marine algae like phytoplankton and sea ice algae, on which Calanus glacialis nibble. This copepod in turn becomes an important source of food for marine creatures, particularly during the long winter months. Calanus stores a large amount of fat, representing about 70 % of its body mass. Marine birds, bowhead whales and Arctic cod are especially fond of the zooplankton, and Arctic cod are in turn rich meals for seals, which are hunted by polar bears.
'In the Arctic Marginal Ice Zones, the ocean is covered with ice in the winter,' says UNIS Professor Jørgen Berge, project manager of CLEOPATRA. 'When the ice finally releases its grip with the advent of Arctic springtime, an explosive production of biomass occurs.'
The team says April is the time of year when the algae living on the underside of the ice start to bloom. These algae are unique in that they can adapt to use as little sunlight as possible. The researchers also probed the development of Calanus glacialis after grazing on the underside of the sea ice. They found that the mature females use the initial bloom peak of biomass production for sex development and egg production.
Another, more extensive, bloom peak of biomass emerges in July, a period when phytoplankton swim in the ice-free waters. It is during this time that the ravenous offspring of Calanus glacialis have grown large enough and eat this bounty of nutrients.
In the second phase of the CLEOPATRA project, the researchers discovered how the development of the copepod occurs during the two distinct algal blooms of the northern Arctic.
The findings show, say the researchers, that changes in the melting of the Arctic sea ice could disrupt the Calanus' cycle. The researchers, from Germany, Norway, Poland, the Russian Federation, Sweden, the United Kingdom and the United States, plan to map the impact of faster melting sea ice on the Arctic's overall food web in the future.