20 year study finds major changes in Southern Ocean plankton

20 year study finds major changes in Southern Ocean plankton

Video transcript

Continuous Plankton Recorder Project Leader, Dr Graham Hosie:

The continuous plankton recorder is a means of mapping the distribution and abundance of plankton. Very quickly and very consistently and very repeatedly over very large areas.

Plankton are the basis of the food web. They are important not only for the food web. They are important for the rest of us in terms of oxygen production, CO2 absorption and we need to map their distribution and abundance to see if it’s changing. If it changes there are consequences for the food web, there are consequences for us.

The CPR is a very simple device, its 1931 technology, it takes in water through a very small aperture at the front as it’s towed behind a ship and traps plankton between two sheets of silk. We then unravel that silk in the laboratory and we have actually got a continuous record of what the plankton existed in the water column over about 450 nautical miles or about 830 kilometres. And at the same time we are recording environmental data so we can match the two, the distribution of the plankton and distribution of oceanography.

The coverage we have got to date is roughly about 70 % around the Antarctic, and to date we have something like about 230 zooplankton species, and probably I think about this stage 70–80 phytoplankton species that we are also looking at.

We are just starting to see indications that we are not seeing as many krill in the sea ice zone as we used to get. We don’t know why, whether it is a change in numbers, a change in distribution or a change in behaviour.

In the sea ice zone, where most of the predators are found during the summer months, the whales, penguins, flying seabirds, it’s a keystone species. These animals have evolved to feed on an organism like krill which are about 50–60 millimetres in size. Now if they disappear or the animals can’t find them to feed on them, they’ll have to either shift their diet to something else, some of the smaller zooplankton, or maybe fish which feed on smaller zooplankton. So there’s consequences higher up, if you start removing keystone species.

We have also been mapping the biogeography of the species, so we have actually now produced a new Atlas on the distribution of what we call our top 50 species. That’s useful for researchers and other monitoring programs they can look in the Atlas and see what species they can expect to see in a certain area.

We need to continue the project, we’ve just set the foundation and we need to continue to look at the potential changes and the consequences. We can use plankton as a bit of an early warning indicating system of what may be coming and what’s happening. It’s the foundation of the whole Antarctic system, if we are not monitoring that part it’s very hard to explain what’s happening elsewhere.

[end transcript]

Continuous Plankton Recorder being deployed from the Aurora Australis
Continuous Plankton Recorder being deployed from the Aurora Australis (Photo: Sandra Zicus)
Expeditioner deploying Continuous Plankton RecorderExpeditioner reading results from the Continuous Plankton Recorder

A 20 year study of the Southern Ocean has found significant changes in the composition, distribution and diversity of plankton and krill sampled by Australian Antarctic Division scientists.

The Division’s Continuous Plankton Recorder project has been mapping and monitoring plankton populations in the Southern Ocean since 1991.

The recording equipment is towed behind a marine science ship, where it filters and catches the tiny organisms.

Project Leader, Dr Graham Hosie, said the research is starting to reveal some interesting trends.

“Since the project began in the early 1990’s there have been significant changes in the composition of plankton in our samples,” Dr Hosie said.

“We seem to be catching less krill in the Plankton Recorder, this could be the result of either a decline in numbers or a change in distribution.

“If there is a permanent decline in krill abundance this may force animals that are dependent on krill, such as whales and penguins, to change their diet in order to survive,” he said.

The research has also found increased numbers of smaller zooplankton in samples from the sea ice zone and sudden massive blooms of other plankton species spread over large areas.

“We are not certain what is driving this change in the Southern Ocean, but documented changes in sea-ice and ocean temperature are already affecting the Antarctic food web,” he said.

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

The 20 year study has also produced 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).

The Continuous Plankton Recorder will be deployed again on the Aurora Australis on the first voyage of the Australian Antarctic season departing Hobart today.