In the game of climate change, you win or you die. At the bottom of the world, who comes out on top?
According to a new study published today in the journal Frontiers in Marine Science, Antarctic animals like krill and the penguins that subsist on them might be among those most vulnerable to rising global temperatures and retreating sea ice. While other species might benefit from habitat expansion in the short term, the radical rejiggering of this delicate landscape could eventually push even the hardiest animals to the limits of survival.
Situated at the southernmost tip of our planet, Antarctica remains one the most sparsely settled environments on Earth. But even in this far-flung locale, the fallout from human industrialization has already begun to take effect. In the past several years, ice loss in Antarctica has at least tripled, spurring sea level rises worldwide. Temperatures continue to creep upward in shallow pockets of the Southern Ocean, while increased emissions of greenhouse gases have dumped acidifying carbon dioxide into the waters. All this could spell trouble for many of the myriad species that call this region home.
“The atmosphere is now changing more rapidly than most of the Earth’s species have ever experienced, certainly in the last million years,” says study author Simon Morley, a marine ecophysiologist at the British Antarctic Survey in the United Kingdom. “It’s critical that we understand the impact that’s going to have… especially in this extreme environment.”
But the umbrella of climate change covers a wide range of factors unlikely to affect Antarctic animals in the same way. To pinpoint the species most likely to benefit or suffer in the short-term, Morley and his colleagues devised a risk assessment model that predicted the impacts of eight different climate-related factors on 31 groups of Antarctic fauna ranging from corals to humpback whales. By tallying data documented in previous studies from the past four decades, the team calculated a numerical score for each species or species group that reflected their resilience to impending change. Higher, positive scores denoted “winners,” while “losers” were those that had accumulated the most projected negative impacts.
Based on the analysis, several species stuck out as particularly susceptible, including temperature sensitive invertebrates like Laternula elliptica clams. While these bivalved critters are equipped to handle brief upticks in temperature, long-term warming could curb their numbers. “How long heat waves are sustained—that’s the game changer,” says Kirstin Holsman, a marine ecologist who was not involved in the study. “A lot of these animals don’t have the physiological capacity to deal with sustained warmer temperatures.”
The decline of sea ice was also projected to cripple certain species, including krill, the tiny, ubiquitous, shrimp-like crustaceans that form the foundation of countless marine food chains worldwide. Krill depend on sea ice as a potential source of food and shelter, and the loss of this precious resource could trigger a mass exodus out of Antarctic waters—or worse, an epic decimation. This could then imperil the many predators who feed on krill, including Adélie and chinstrap penguins, both of whom fell out as “losers” in the researchers’ model.
A third penguin species, the emperor penguin, also fared poorly in the risk assessment. Unlike their relatives, emperor penguins include krill in their diet as only a supplement to fishy flesh—but because these blubbery birds rely on fragile sea ice and ice shelves as breeding grounds, they received one of the most concerning scores of any species included in the study.
In the end, however, Morley was surprised to find that more species came out ahead than not. The main driver here, he says, is the expansion of certain habitats. As the sea’s iciest habitats fade, open sea and ocean floor will take their place, enabling sea star and urchin species that tend to settle in these zones to expand their boundaries. In the short-term, it seems, animals like these could actually thrive in the face of changing climes.
But, Holsman points out, not all species hold an equal share of the Antarctic playing field. “Some of these are key species that are far more influential than others,” she says. “Krill, for instance, support many predators in the system, including humans that fish for them.” In other words, the decline of one species isn’t cancelled out by the growth of another. In complex ecosystems, survival becomes something of a game of chess. Despite their size, krill are some of the most important pieces on the board—and it can spells serious trouble if the queen is among the first to fall, even if several pawns are left standing.
Even for the animals whose numbers are boosted in the short term, Holsman adds, these benefits only go so far. And, as Morley points out, some of this flexibility is contingent on the availability of alternative habitats. And animals are quickly running out of options.
As global temperatures have risen, some species have sought solace from the heat by migrating south. But in the Antarctic, there’s only so far they can go. Here, “it’s already pretty much as cold as it gets,” Morley says. If climate change continues on its current trajectory, conditions could eventually reach a tipping point, past which the fates of many more species might spiral be in jeopardy.
Ultimately, however, predicting the future remains a hairy pursuit, especially considering that much of the Antarctic remains vastly unexplored. “We still haven’t described, by a long way, all the species that live here,” Morley says. What’s more, Antarctica’s vast landscape is far from uniform: Partitioned into different locales, even animals of the same species might not experience change in the same way.
These gaps in knowledge can make some interpretations difficult, says Angelika Brandt, a marine zoologist and Antarctic biodiversity expert who was not involved in the study. Of the 23 groups assessed in the study, only 15 were able to assess animals at the species level; the other eight examined larger groups that included multiple species, each of which might respond differently to the effects of climate change, Brandt says.
Even when focusing on a single species, predicting adaptability is no easy task, points out Bettina Meyer, an Antarctic ecologist who was not involved in the study. Meyer’s work, which centers on the region’s krill, has shown that their dependence on sea ice is more complicated than once believed. For the time being, Meyer says, the malleability of these populations is still a little up in the air.
But Holsman believes the results of the study are meant to be more suggestive than prescriptive. Antarctica’s harsh conditions don’t exactly make for easy data collection—so while research continues, it’s important to continually assess the information that’s been gathered so far. “This is a region that doesn’t have a lot of regular monitoring,” she adds. “It’s just so remote. So the first step is to try to do these types of risk analyses… and use them to prioritize which aspects to focus future research on. This is how we might identify vulnerable species for more quantitative, in-depth analysis.”