Seabird populations in the South Atlantic and Southern Ocean are facing direct and indirect impacts of climate change due to rising temperatures and ocean acidification. However, long-term monitoring of seabird populations in the South Atlantic and Southern Ocean typically only began in the 1950s, posing a challenge to understanding the long-term responses of seabirds to global change.
Dulcinea Groff, a University of Wyoming postdoctoral research associate with the Wyoming Established Program to Stimulate Competitive Research (EPSCoR), led a study that put together a puzzle of the 14,000-year-old record of tussac grasslands in the Falkland Islands.
“First, the 14,000-year-old record raises a very troubling question about where seabirds will go as the climate continues to warm because the seabirds at Surf Bay established during cooler climates,” Groff says. “Seabird conservation efforts in the South Atlantic should be prepared for these species to move to new breeding grounds in a warmer world, and those locations may not be protected. Second, we show just how important the nutrients in seabird poop are for the ongoing efforts to restore and conserve their grassland habitat.”
Groff is lead author of a paper, titled “Seabird Establishment During Regional Cooling Drove a Terrestrial Ecosystem Shift 5,000 Years Ago,” that appears in Science Advances. The journal is the American Association for the Advancement of Science’s (AAAS) open-access multidisciplinary journal, publishing impactful research papers and reviews in any area of science, in both disciplinary-specific and broad, interdisciplinary areas.
At the time of the study, which took place on separate trips during 2014 and 2016, Groff was a Ph.D. student at the University of Maine. The work is a chapter of her dissertation. Others who contributed to the paper were from the University of Maine, the University of Hong Kong and the South Atlantic Environmental Research Institute in Stanley, Falkland Islands.
Seabirds first came to the Falklands approximately 5,000 years ago, just as the region was cooling, the study says. Seabirds there are situated by the parts of the tussac grass the birds use. For example, some seabirds use the soft peat beneath the tussac to burrow into and make their nests, Groff says. These include the Magellanic penguin, white-chinned petrel, thin-billed prion, common diving petrel, Falkland diving petrel, sooty shearwater and great shearwater.
There are ground-level nesting seabirds like the Southern rockhopper penguin, as well as seabirds that commonly nest adjacent to the tussac grass. These include the black-browed albatross, gentoo penguin, rock shag, South American tern, kelp gull and imperial cormorant.
Marine-derived nutrients from bird guano facilitated tussac establishment, the paper says.
Within 200 years after seabirds established at Surf Bay, the plant community changed from a mixture of shrubs and grasses to being dominated by grasses. As a result, the fire activity increased in these grasslands.
“We’re not sure exactly why fire activity increased, but grassland fires are known to be controlled more by the amount of fuel available on the landscape and less by how dry the conditions are at the time,” says Groff, who also is a research fellow at Lehigh University. “For this reason, we suggest that either there was more lightning to start the grassland fires or there was more fuel on the landscape for the fire to burn because of the increase of these grasslands. What’s fascinating is that fire is a natural part of this ecosystem, and this is something we knew little about before.”
To compile the 14,000-year-old record, the research group collected a peat profile for pollen and charcoal analyses, and reconstructed seabird populations of the past.
“Peat is a natural archive of information about past environments because it preserves the remains of plants and animals really well as it accumulates or builds up over thousands of years,” Groff says. “We examined pollen made by the plants; charcoal left over from grassland fires; and chemical indicators associated with seabirds being present, which all get preserved in the peat as it accumulates over time.”
The peat profile allowed the research group to determine the order of events with the seabirds and their breeding habitat, the tussac grasslands.
“I think of it as a ‘which came first, the chicken or the egg?’ scenario,” she says. “By counting the number of pollen grains and pieces of charcoal, and examining the chemistry of the peat profile, we learned that seabirds arrived before the establishment of the grassland.”
The group also took a look at an extinct predator called the “warrah” or Falkland Islands wolf that could have caused seabird abandonment and redistribution of ground nesting seabirds. However, the impact that the warrah would have had on the seabirds in the Falkland Islands is unknown.
“Using a technique called radiocarbon dating, we were able to determine the age of warrah fossils,” Groff says. “The ages tell us that the warrah was in the Falkland Islands by at least 3,500 years ago, at the same time that seabirds were there.”
A warming South Atlantic casts doubt over the future of the Falkland Islands as a long-term seabird breeding hot spot. Conservation efforts focusing on tussac restoration should include this terrestrial-marine linkage, although a warming Southern Ocean calls into question the long-term viability of the Falkland Islands as habitat for low-latitude seabirds, according to the paper.