Southern Ocean plankton is changing

A 20 year study of the Southern Ocean has found significant changes in the composition, distribution and diversity of plankton and krill.

The Australian Antarctic Division’s Continuous Plankton Recorder project has been mapping and monitoring plankton populations in the Southern Ocean since 1991 (Australian Antarctic Magazine 13: 12–13, 2007). The recording equipment is towed behind ships, where it filters and catches the tiny organisms.

Project Leader, Dr Graham Hosie, said that since the project began in 1991 there have been significant changes in the composition of plankton in the samples.

‘We seem to be catching a lot more smaller plankton compared to krill; notably copepods which, like krill, also graze on phytoplankton,’ he said.

‘We don’t know what is causing this or if competition for the same food will affect krill. But any change from krill to smaller zooplankton may force animals that are dependent on krill, such as whales and penguins, to change their diet in order to survive.

‘We have also observed sudden very large increases in foraminiferans — a calcareous, single-cell zooplankton. While these blooms are short lived, they suppress other zooplankton numbers. But again, we don’t know if this has a flow-on effect to higher animals.’

The project has covered 70% of the Southern Ocean, taken 30 000 samples, identified and mapped 230 species and towed the plankton recorder for more than 278 000 kilometres.

The 20 year study has also resulted in the first Zooplankton Atlas, which documents the distribution and abundance of the 50 most common zooplankton species in the Southern Ocean.

The atlas will serve as a reference for other Southern Ocean researchers and monitoring programs such as those run by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and the developing Southern Ocean Observing System (SOOS).


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