As the waters around Antarctica warm up over the next century, almost 80 percent of invertebrate species living on the seafloor will see their habitats shrink. Coupled with other threats such as pollution and loss of ice, that could eventually result in some of these species to go extinct.

Researchers at the British Antarctic Survey in Cambridge looked at 963 invertebrate species — including sea spiders, clams, and a variety of corals — inhabiting the Southern Ocean, the expanse of water surrounding Antarctica. They found that while some of the species will fare better in warmer waters, most of them will suffer — some losing almost half of their current range. Though these creatures live at the bottom of the sea, far from sight, they play important roles for the ecosystem, recycling nutrients and providing food for larger animals. The findings were published today in the journal Nature Climate Change.

As the world keeps warming because of human-made climate change, the waters around Antarctica are projected to warm by an average of 0.4 degrees Celsius by 2099. That might seem like a small change, but the consequences are significant. The Southern Ocean is home to species that adapted to live in some of the coldest water on the planet — so even a tiny variation in temperature can mean a lot, says study co-author Huw Griffiths at the British Antarctic Survey, who’s been studying marine invertebrate for 17 years.

Griffiths calls these creatures “all the ugly things with no legs, or lots of legs, or no eyes, or lots of eyes.” They are starfish, sea spiders, sea urchins, worms, snails, clams, sponges, and crabs that live on the sea floor, eating dead plankton, mud, and poop from other marine animals. “All the things that are less glamorous and cuddly than penguins and seals but are very important for the ecosystem nonetheless,” Griffiths tells The Verge.

Griffiths and his colleagues found that even a slight temperature increase of 0.4 degrees Celsius could put some of these creatures in danger. The biggest losers are those invertebrates that are adapted to live in very cold waters, such as the Ross and Weddell Seas to the north and south of the continent. A sea urchin called Sterechinus diadema could lose as much as 43 percent of its habitat, while the sea spider Austrodecus simulans could lose 38 percent of its range. All in all, 79 percent of the seafloor-dwelling species will see their habitat shrink, the researchers found.

But not all species will suffer, Griffiths says. Creatures that can live in warmer waters, and can survive at different temperature ranges, could actually gain some ground. The biggest winners could come from South Georgia, islands in the southern Atlantic Ocean. That’s because the waters of the West Antarctic Peninsula are projected to warm to similar temperatures as present-day South Georgia — expanding the habitat for some of the vertebrates. The king crab Paralomis formosa, for instance, could see its habitat balloon by 255 percent.

But there’s a caveat: Antarctica is surrounded by one of the strongest sea currents in the world, which helps keep the area cold. So the newly available habitat would be incredibly hard to access for these seafloor creatures, Griffiths says.

Losing habitat per se won’t cause these invertebrate to go extinct, Griffiths says. But climate change won’t only make ocean waters warmer, it’ll also make waters more acidic, for instance, which harms some animals’ ability to make shells. Coupled with human pollution, all these stressors could cause these animals to disappear in the long run. And that’s dangerous, because this community of bottom-dwellers keep nutrients circulating in the ocean waters by eating dead plankton and poop. Crabs and spiders also provide food for other animals, while corals can provide hiding for small fish.

The findings can help inform future management of the region: the areas most at risk could be protected from human development, fishing, and tourism, for instance, just as we protect certain land areas in Antarctica. But, most of all, the study shows how even just a slight warming in ocean waters could have catastrophic effects for the species living there. “If the weather goes up by .4 degrees in a day, I don’t notice it. For me, that’s nothing,” Griffiths says. “A change that I wouldn’t even perceive in my normal day life could be that important.”