About half of the two dozen Antarctic species that Peck has studied seem to do fine in water 2 °C warmer than current maximum summer temperatures — but the rest seem to suffer. “At least two of the species that we think are going to be the first [to disappear] could give problems for the balance of the ecosystem,” he says. Those are the Antarctic clam (Laternula elliptica) and the shallow-water brittlestar (Ophionotus victoriae), both mainstay species that eat dead plankton and other organic trash that falls from above, and turn it into the biomass that feeds everything else on the sea floor. But these species either die or become dangerously sluggish at even 1 °C above current summer highs — temperatures that could become widespread in 50–100 years.
If rising temperatures cause brittlestars and clams to disappear, then more falling detritus might be consumed by microbes instead of being converted into edible biomass — meaning that it would sustain fewer animals, overall, on the sea floor. Alternatively, filter-feeding sponges might multiply to fill the niche. Either way, the mix of species supported further up the food chain might no longer include large numbers of archaic predators such as starfish, ribbon worms and sea spiders.
Julian Gutt, a marine ecologist at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, admires Smith's work with the crabs, but withholds final judgement on whether the crustaceans are a new piece of this destructive puzzle, or a long-present fixture. Repeat surveys showing that the crabs are expanding their foothold over time would confirm an invasion, he says. But “if they move into new habitat, some serious impact is quite likely”.
Aronson, for one, will be watching closely for signs that this is happening. And in his experience, optimism is not warranted. “Every time we make a prediction of what we think will happen in the next 50 years, then poof, 10 years later, there it is,” he says. “So I think this is going to be happening more rapidly than, as conservative scientists, we're used to predicting.”