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Spot the difference – marine life at the poles

Krill (Euphausia superba) are small, shrimp-like animals that grow up to about 6 cm in length and live for up to 5 years. Krill usually live in dense swarms which may have more than 10,000
Krill (Euphausia superba) are small, shrimp-like animals that grow up to about 6 cm in length and live for up to 5 years. Krill usually live in dense swarms which may have more than 10,000

Presentation summary for the IPY Science Conference 2010 in Oslo by Dr. Geraint Tarling

An International Polar Year study sheds new light on the fundamental differences between marine ecosystems and food webs in both the Arctic Ocean and the Southern Ocean that surrounds Antarctica. The findings have important implications for the sustainable management of polar fisheries and for food security.

Through studies of long-term observations of the Southern Ocean ecosystem scientists conclude that, as a general rule, in ocean communities similar amounts of *biomass occur in animal groups of different body sizes. For example by knowing how many *zooplankton live in the ocean, the populations of fish living off these microscopic floating animals can be estimated, since the biomass of both groups should be roughly the same. That is providing that the fish have not been already exploited commercially.

Although this rule works well in the Southern Ocean, the picture is different in the Arctic. The best explanation of this difference features the role of krill (shrimp-like invertebrates), which dominate the Southern Ocean. These herbivores mainly eat *phytoplankton. However, in the Arctic, krill is replaced by larval fish which eat zooplankton, especially copepods, so decreasing their numbers. This throws out the general size-based rule.

Session information

Speaker:
Dr. Geraint Tarling

Contact:
Mobile: +44 (0)7910 186486
Email: gant@bas.ac.uk

Tuesday 8 June @ 15.15
Session: T3-8

This work highlights the major differences between both polar oceans. In the Arctic the number of organisms in each species appears to be controlled from the top of the food chain, whilst in Antarctica the reverse is true. It is more difficult to predict the number of Arctic fish stocks than it is to predict krill numbers in the Southern Ocean surrounding Antarctica.

Definitions

Biomass
living matter
Zooplankton
microscopic floating animals
Phytoplankton
microscopic floating aquatic plants