Changing Oceans Put Crabs Into 'Survival Mode'

It has long been suspected that rising temperatures and ocean acidification are making it harder for crabs to reproduce and survive. However, aside from weakening exoskeletons, it was unclear exactly why this was happening. Now, a new study suggests it comes down to these crustaceans' own biology.

That's at least according to a new study published in The Journal of Experimental Biology, which details how the vulnerable porcelain crab (Petrolisthes cinctipes) has recently had to put a great deal more energy into basic survival functions than it used to, leaving less energy for other behavior.

And when we say "basic functions," we mean extremely basic. The crab, which lives in rocky shorelines along the Indian and Pacific Oceans, was observed laboring to just eat and breathe from day to day, often too tired to hide from predators or reproduce.

This is also rather different from how ocean acidity and temperature affects seafloor- dwelling crabs, which are primarily harmed by acidification because of how it interferes with the calcification of their exoskeletons.

Study co-author Jonathon Stillman told Carbonbrief that this may be a sign of things to come, where "future intertidal zone (seashore) animals may experience reduced rates of growth, behavior, or reproduction."

Stillman adds that it's harder to understand shoreline conditions because temperatures in the zone can change by about 36 degrees Fahrenheit (20 Celsius) within a quarter of a day, while water acidity can vary with season and time of day.

To keep things consistent, Stillman and his colleagues focused their study around the autumn season, testing the conditions of peak acidity and temperature during the average fall day.

They simulated these conditions and others, like high and low tide, in a lab, running three scenarios in all on controlled test crabs.

Stunningly, after two-and-a-half weeks, they found that the metabolic rate of these crabs fell as much as 25 percent, meaning they weren't using their energy nearly as efficiently. They also found that as acidity and temperature rose, so did the crabs' biological means of thermal tolerance, indicating that more energy was being dedicated towards this survival mechanism than growth or practically anything else.

So while these crabs are adapting to survive unfavorable conditions, their adaptations could likewise lead to fewer and fewer offspring each new generation - an example where survival of the individual does not mean survival of the species.