Volcanic eruptions nearly wiped out this Antarctic penguin colony

One of the oldest gentoo penguin colonies was periodically pushed to near extinction, but it always bounced back.

Ardley Island’s gentoo penguin colony is one of the largest and oldest on the Antarctic Peninsula. New research examining penguin guano in the sediment of the island’s lake shows that the colony not only stretches back an impressive 7,000 years, but that it was pushed to near extinction at least three times. When volcanic eruptions blanketed the island in ash, the penguins were either killed or forced to abandon it. Each time, it took the colony 400-800 years to recover. Stephen Roberts of the British Antarctic Survey (BAS) tells us more.

ResearchGate: What motivated you to investigate historical changes in penguin populations on Ardley Island?

Stephen Roberts: Over the last 15-20 years, the British Antarctic Survey (BAS) has been working with several international collaborators to examine the impact of past climate change on terrestrial glaciers and biodiversity in Antarctica. While working on lake sediment cores collected from the South Shetland Islands, we noticed that the 8,500-year-old sediment record from Ardley Island had some unusual and interesting changes in geochemistry that were different to those we had seen in other lake sediment cores from the area. We also found several penguin bones in the Ardley Lake core. As these were not present in the any of the other cores, we decided to investigate what had happened on Ardley Island further.

Sediment cores were taken from Ardley Lake (above) when it was frozen as this provides a more stable platform for coring. Credit: Stephen Roberts

RG: How were you able to determine past population trends?

Roberts: By undertaking detailed biological and geochemical analysis of the lake sediments, we determined what proportion of the sediment that had accumulated at the bottom of Ardley Lake was made up of penguin guano. We used previously published estimates of how much guano each gentoo penguin on Ardley Island produces per day and other available information to estimate how the population around Ardley Lake might have changed over the 7,000 years since penguins first arrived on the island. Our reconstructed estimates of maximum past colony size are similar to the size of the present-day penguin colony on Ardley Island: about 5,000 breeding pairs.

RG: What did you find?

Roberts: We found that first sustained penguin colony was established on Ardley Island about 7,000 years ago, which pre-dates previous sub-fossil evidence of penguin occupation on the Antarctic Peninsula by about 1,000 years. We had expected the local population to show minor fluctuations in response to changes in climate or sea ice. Instead, we found that three large eruptions from the nearby Deception Island led to the near local extinction of the former gentoo colony on Ardley Island. The volcano had a far greater impact than originally anticipated, and it took the colony on average between 400-800 years to fully recover after each large eruption.

Sediment core extracted from the lake. Credit Stephen Roberts

RG: What exactly happened to the colony after the eruptions?

Roberts: We spent a lot of time thinking about how the colony responded, and assessed the available evidence for clues about possible migration patterns across the Peninsula region. At the moment, the evidence isn’t detailed enough, but similar investigations could be undertaken elsewhere to answer this question. Although, we don’t know exactly what happened to the penguins, there are three main possible outcomes. The first is that they were killed, either from ash fall directly or indirectly through starvation, incapacitation, or habitat disturbance. The second is that the adults escaped by swimming away and that adult penguins out at sea feeding might not have returned to the island. Finally, the penguins may have stayed and struggled through, and there is some evidence of this after one of the big eruption events.

Mature individuals on long forages would have the best chance of survival. If the eruption occurred during breeding season, the chicks and juvenile penguins would be trapped on the island. If parents didn't return from foraging, then the colony could collapse quite quickly. A large eruption could bury penguin chicks in abrasive and toxic ash, and any chicks or juveniles present at the time might be too young to survive in the freezing waters. Suitable nesting sites and materials to build nests can also be buried, meaning that the island could remain essentially uninhabitable for a long time afterwards.

Gentoo penguin and chick in Potter Cove, King George Island. Credit Stephen Roberts

We found that more recent eruptions, from 2000 years onwards, were generally smaller and produced less ash, probably impacting the colony less. Therefore, we think that chances of colony survival depended primarily on the size of the eruption, but also the timing in relation to nesting and life stage of the penguins themselves. One interesting feature that come out of this study is how resilient the Ardley Island colony as a whole has been through time. It does seem to be able to bounce back.

RG: Can these results be used for conservation going forward?

Roberts: The techniques developed in our study could be applied elsewhere in and around Antarctica to reconstruct past changes in penguin colony sizes. This would provide a relevant and valuable long-term perspective on modern-day penguin colony changes, and allow us to better assess the potential impact that changing climate and sea-ice conditions—as well as any nearby volcanoes—can have.

Featured image courtesy of Ronald Woan.