You’ve heard that dark chocolate can be good for your health, but you’ve probably also heard that just a little piece can be toxic to your dog. What’s good for one species may be deadly for another, and vice versa. A new example: Researchers say that, unlike fish, populations of octopuses, squid, and cuttlefish have actually increased during the last six decades of climate change. The findings were published today in the journal Current Biology.
The cephalopod (literally “head-footed”) family is one of the most remarkable on Earth. Octopuses, cuttlefish, and squid are squishy, strange invertebrates. As such, it was assumed for a long time that they were unintelligent automatons, completely at the mercy of instinct. We now know that nothing could be further from the truth. These astonishing animals have gifts and skills that humans could only dream about.
They also have a triad of traits—short lifespans, flexible development, and rapid growth—that allow them to adapt when other species are going belly-up. Even so, researchers did not expect to find them doing quite this well. In fact, lead author and University of Adelaide biologist Zoë Doubleday was inspired to begin this project by reports of shrinking populations of giant Australian cuttlefish (pictured above).
Doubleday and her colleagues reviewed fishing data on cephalopod catches from 1953 to 2013. Their dataset included information from all over the world about species found in both open water and on sea floors, and included targeted fishing species as well as bycatch.
Their results suggest that, far from declining in rapidly warming waters, cephalopod populations are actually on the rise. “This is remarkable given the enormous life-history diversity exhibited across these groups,” the authors write, “which were represented in this study by 35 species/genera and six families.”
The uniform increase across species, families, and regions suggests that global trends are at play. Earlier studies had suggested (and the authors of the current study believe) that warming waters might truncate cephalopods’ short life spans even further. And yes, a shorter life span is bad news for an individual, but cramming a lot of generations into a short period of time allows a species to adapt more quickly.
The authors also speculate that, as fish populations shrink, cephalopods may finally be getting some relief from predators and rivals for resources.
But let’s not throw an octopus parade just yet. This study focused on a small subset of cephalopod species, notes Mark Carnall of the Oxford University Museum of Natural History. Additionally, he wrote in an email to mental_floss, “even live cephalopods are hard to identify,” and data collection can vary between and even within countries. On top of that, “many species of cephalopod are only known from a handful of specimens, so data about their diversity is thin on the ground.” And some species, like the highly traded chambered nautilus, are definitely in decline or locally extinct.
Ecosystem dynamics are never simple. An increase in cephalopod populations, if it's happening, could feed, and thus increase, populations of cephalopod predators. Additionally, as fish stocks shrink, humans are turning more to fishing for octopus and squid. And warming waters are not the only product of climate change: Our oceans are also gradually acidifying, which may affect even these resilient “weeds of the sea.”
Editor's Note: This post has been updated to reflect additional insight from an outside expert.