Fishing - Antarctic style

Drilling a hole in the ice to go fishing! Photo: Joseph Muldoon

Sampling different parts of the Antarctic food web

31 May 2024

How will Antarctic foodwebs and biodiversity change under a changing climate and shifts in sea ice dynamics? Platform researchers have been sampling different parts of the Antarctic foodweb in order to answer this question.

The food web structure and the flux of organic matter and nutrients through food webs to the top levels are fundamental components of functioning ecosystems. These are the processes that support biodiversity and productivity of whole ecosystems.

To study these processes, the team use advanced forensic techniques to analyse samples that represent different parts of the Antarctic food web, from the sea ice algae that grows in the matrix of frozen seawater to invertebrates, fishes penguins and seals.

They can use chemical tracers for the energy and organic matter produced by sea ice algae, and track the flow of that material all the way to the top of the food web. So, sampling guano from penguins and scat from seals can provide a way to test how the structure of the food web changes from place to place and from year to year as the environment changes.

Water sampling is used to test for the presence of different animals to further inform data on food web structure. This leads to a better understand the role of animals in supporting productivity in the system, by tracking the recycling and delivery of limiting nutrients to the coastal zone.

Ice fishes

In the 2023/24 summer Antarctic field season, the team collected fish and eDNA water samples from multiple sites around McMurdo Sound for analysis of food web dynamics. In real terms, this means ice fishing!

Samples of water were collected from a range of sites around Ross Island with different levels of sea ice dynamics, as resolved by satellite imagery. These samples are being extracted and the DNA sequenced to provide information on the biodiversity present at each location.

Ice fishes (Trematomus spp.) were collected from the same range of sites and they are being analysed for differences in the structure of the underlying food web among sites using chemical tracers of organic matter and nutrients. The team hope to repeat this sampling next field season for comparison, and also to compare results with samples collected from other regions of the Ross Sea during voyages on the RV Tangaroa under the Antarctic Science Platform.

Sorrel O’Connell-Milne ice fishing

Sorrel O’Connell-Milne ice fishing to collect fish samples for analysis. Photo: Joseph Muldoon

Penguin guano and seal scat

The field team collected Adélie penguin guano and Weddell seal scat samples from Cape Royds, Cape Bird and sites around Ross Island near Scott Base and Cape Evans for dietary, genetic and biogeochemical analyses.

Analysis of the prey that penguins and seals are feeding on will be accomplished with DNA analysis coupled with isotopic and trace metal analysis of both guano and scat. These data can be compared among sites along the gradient in sea ice cover to make connections between food web linkages to the top levels of the food web under different sea ice conditions, links to the open ocean pelagic environments, and also with data from previous year’s sampling. The team are also analysing the limiting nutrients that are brought onshore by these animals and the food web (trophic) position of penguins and seals feeding under different environmental conditions. Penguins and seals serve as effective sentinels for the state of the marine ecosystem in this context, and provide important information about how changing environmental conditions in Antarctica influence ecosystem function.

The field team led by Stephen Wing (University of Otago) included Joseph Muldoon, Katie Nelson, Sorrel O’Connell-Milne (University of Otago) with help from Ian Hawes (University of Waikato). Analysis is being carried out by these individuals and collaborators, Gert Jan Jeunen (University of Otago) and James Leichter (Scripps Institution of Oceanography).

Group photo of team sampling Antarctic foodweb

From left, Joseph Muldoon, Stephen Wing, Sorrel O’Connell-Milne and Katie Nelson. Photo: Joseph Muldoon