Delicate balance in the Falklands

Seabird droppings helped shape the delicately balanced ecosystem of the Falkland Islands, which is in danger of abrupt collapse as the climate warms, a new study shows.

A long-term palaeoecological reconstruction, described in a paper in the journal Science Advances, reveals that seabirds first flocked to the Falklands 5000 years ago as the region was cooling.

Today, the sub-Antarctic islands are a refuge for some of the world’s most important breeding colonies, including Great Shearwaters, White-chinned Petrels and five species of penguin.

On these windswept and treeless outposts, the birds breed in the natural tussock grasslands along the coast, which offer protection, food, and nesting sites and materials. In the past two centuries, however, this breeding habitat has been severely depleted by sheep grazing and erosion.

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A rookery of Southern rockhopper penguins (Eudyptes chrysocome chrysocome). Credit: Dulcinea Groff

Seabird populations are also threatened by rising temperatures and increasing ocean acidification, but the extent of their sensitivity is difficult to predict, as long-term monitoring only began in recent decades.

Now, research led by the University of Maine, US, has turned to the fossil record to fill the gaps, piecing together the interactions between seabirds and the islands over thousands of years.

During expeditions in 2014 and 2016, the team collected a 476-centrimetre peat column from Surf Bay in East Falkland. This thin cylinder of organic material recorded 14,000 years of environmental history in its layers, allowing the researchers to trace the development of the link between the terrestrial and marine ecosystem.

For the first 9000 years of the record, the islands were dominated by low levels of grasses, ferns and dwarf heather-like shrubs.

Then, 5000 years ago, an abrupt transition occurred as the region cooled. Seabirds established colonies on the islands, and within 200 years tussock grasslands became the dominant vegetation. The high concentrations of guano deposited by the seabirds shaped the terrestrial ecosystem, nourishing the grass, producing peat, and increasing the frequency of fire.

“We know that many seabirds in the South Atlantic rely on these unique coastal grasslands, but it turns out that the grasses also depend on the nutrients seabirds provide,” says Maine’s Jacquelyn Gill, a co-author of the study.

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Tussac grasslands that form deep peat deposits can be found eroding along coastlines in the Falklands. Credit: Dulcinea Groff

“Because they rely on ecosystems in the ocean and on land for their survival, seabirds are really good sentinels of global change.”

This careful balance supporting the Falklands ecosystem also makes it sensitive to changes in land use and climate.

According to lead author Dulcinea Groff, this research raises the question of where seabirds will go as the climate warms.

The absence of seabirds from the study site prior to 5000 years ago indicates that they are sensitive to temperature change; warmer sea surface temperatures may, for example, impact their food supply.

Groff, who is now based at the University of Wyoming, notes that “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”.

In the paper, the researchers issue a final warning: “As the Southern Ocean continues to warm in the coming decades, the Falkland Islands seabird communities may undergo abrupt turnover or collapse, which could happen on the order of decades.”

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