It's time to depart South Georgia and head back to Stanley. We're sad to leave the island and our survey, but pleased with what we have accomplished on this trip.
Map of sampling sites (2021 survey sites in red). Credit: SAERI/SMSG
It's time to depart South Georgia and head back to Stanley. We're sad to leave the island and our survey, but pleased with what we have accomplished on this trip. In total, we have completed 82 survey dives, spending more than 3131 minutes underwater. The seaweed team spent 58 hours ashore, surveying ten sites. Jo completed 34 oceanographic sampling events in the fjords. We've collected over 720 seaweed samples, 86 sponge samples and over 200 samples of other animals. We've spent over 567 hours in the lab processing them. All this information builds on our survey from 2010 and will help us understand South Georgia's shore and shallow subtidal biodiversity. The compressor that fills our dive tanks has pumped over 100,464 litres of air, and we estimate we've drunk 720 cups of tea!
A selection of the seaweed and animal diversity the team recorded during the survey. Credit: Claire Goodwin
As we reflect on the survey, we all remarked that there seemed to be an increased amount of fresh meltwater in the sea compared to our trip ten years ago. There also were far fewer fur seals on the beaches. Ten years ago, at the same time of year, it was difficult to move due to the number of fur seals, and we were mobbed by them on most dives. Talking to British Antarctic Survey scientists at the King Edward Point Base, their early impression was that females had yet to arrive, and the numbers of males seemed low. We’ll look forward to hearing how the season progresses in South Georgia. If the two observations are related is not clear – we were here a week earlier in the season than 2010, so we could be seeing natural variability in weather and timing of mammals. However, South Georgia is thought to be in a region that may be particularly sensitive to climate change, affecting weather and food sources for top predators such as fur seals.
I chat with Jo Zanker, a PhD student from British Antarctic Survey, who is collecting data for her project on the trip. Jo is creating a computer simulation of how the water circulation in Cumberland Bay, a large Fjord in the middle of South Georgia's north coast, is changing. She has been deploying a CTD instrument that measures conductivity (salinity), temperature, and depth of the water column. The CTD readings will give her data to include in her model and make it more accurate. Sea surface temperatures around South Georgia are rapidly warming – since 1925 they have increased by an average of 0.9°C in the summer and 2.3°C in winter. Jo explains that the water circulation in the fjords brings this warmer seawater to the faces of glaciers and melts them. The freshwater from the melted glaciers also alters the circulation in the bay. By understanding water circulation in fjords, we can understand and predict glacier retreat (melting) and consequent sea-level rise. The Neumayer Glacier in Cumberland Bay has retreated more than 5 km in the last century. The Nordenskjöld Glacier, which was previously stable, is now also retreating. Alterations in water circulation could affect the whole ecosystem. They may change the distribution of krill and small fish, which feed birds, seals, and whales. They could also affect commercial fisheries. Polar Seafish Ltd fund Jo’s research, and they will benefit from her model through improved understanding of the MSC certified sustainably managed ice fish fishery.
Jo deploys a CTD in one of South Georgia's fjords. Credit: Claire Goodwin
One spectacle we did not see in 2010 were whales, however 11 years on, this trip was very different. One morning on the trip back, I am having a rare lie-in, enjoying not having to get up for diving when there is a knock on my cabin door. 'Quick, whales!' I am alerted. I speed dress, grab my camera, and dash up on deck. I hear an exhale as a humpback dives, just of the bow. Looking out to sea, I can see hundreds of whale blows on all sides of the ship. Clouds of albatrosses and Cape petrels skim over the sea around them. The light hits the oil droplets in the whale's exhaled air, making rainbows. We've slowed down to avoid collision while the captain carefully steers around the whale groups. For the next hour, we drift along with them, in awe at their company.
Hundreds of whales surrounded the Pharos. Credit: Claire Goodwin
Humpback whales diving. Credit: Claire Goodwin
The oil in the whale blows created rainbows. Credit: Claire Goodwin
South Georgia is a crucial summer feeding ground for several whale species, including Humpbacks and Blue Whales. The whaling industry, which killed over 175,000 whales in sixty years, nearly wiping them out. But now, after 30 years of protection, whale populations are recovering. However, there is a new threat – climate change. Humpback whales, fur seals, albatrosses, and many other species around South Georgia thrive by eating krill. These shrimp-like planktonic crustaceans are around 6 cm long. They can form swarms as dense as 10,000 individuals per cubic metre. Over 500 million tonnes of krill are estimated to exist in the Southern Ocean, making it one of the most abundant animal species in the world. Krill are not born in South Georgia but are brought up from the Antarctic by a cold current. Their nursery is the winter sea ice, where they feed on algae growing on the ice's underside. This sea ice habitat is decreasing as climate change causes it to melt. Less habitat will result in fewer krill - scientists have shown that summer krill densities correlate positively with sea ice densities the previous winter. So, the source of South Georgia's krill may be threatened. To compound this, as sea temperatures rise around South Georgia, they are likely to become warmer than adult krill that do arrive here can tolerate. Scientists also expect that warming will reduce the amount of phytoplankton around South Georgia; adult krill feed on this microscopic algae. There is some annual variation in krill abundance around South Georgia; every few years, the krill conveyor belt current seems to fail, resulting in diminished krill numbers. But even allowing for this variability, there is an overall declining trend. Less krill will have a significant impact on not only top predators but South Georgia's entire ecosystem.
Something that will help South Georgia's marine life is that the government established one of the world's largest Marine Protected Areas (MPA) in 2012 to protect the rich biodiversity present in its waters. This MPA covers an area of 1.24 million km2, that's 17 times the size of New Brunswick! Measures to protect marine life include No Take Zones, where all fishing activity is banned. These cover the most biodiverse areas of seabed, some 283,000 km2, including all coastal waters of less than 100 m depth, plus features like hydrothermal vents, seamounts, and trenches. Additionally, fishing on the seafloor is prohibited over 94% of the Marine Protected Area. The MV Pharos SG enforces these measures – should there have been a report of illegal, unreported and unregulated (IUU) fishing during our survey, we would have had to drop tools and investigate. It is estimated that 15-30% of global fish catches are from IUU fishing, so the government needs to remain vigilant; the year-round presence of the MV Pharos SG is a significant deterrent. A five-yearly review process for the MPA is in place, as well as a scientific data portal and research and monitoring plan. With challenges such as global warming and illegal fishing facing it, the more data available about South Georgia's rich marine realm, the better. Our survey has provided much need information on the coastal biodiversity of this inspirational island. We all feel honoured to have experienced such a wild and wonderful place and hope that South Georgia's unique wildlife will thrive in the future. So now it's time to hit the lab and identify our samples. And perhaps start planning for a survey of South Georgia's largely unexplored south side….
Map of South Georgia and the South Sandwich Islands MPA. Credit: Government of South Georgia and the South Sandwich Islands
Panoramic view of Cumberland Bay, South Georgia. Credit; Steve Brown
Want to read more?
South Georgia and the South Sandwich Islands MPA
Sylvester Z et al. (2021) Detecting Climate Signals in Southern Ocean Krill Growth Habitat. Frontiers in Marine Science 8
South Georgia and the South Sandwich Islands MPA
https://www.gov.gs/environment/marine-protected-area
Brower K (2013) Life in Antarctica Relies on a Shrinking Supply of Krill. National Geographic.
Return of the Whales to South Georgia
https://www.bas.ac.uk/media-post/return-of-the-whales-to-south-georgia/