As we continue to change the world’s oceans and alter marine habitats, cephalopods are booming. Numbers of octopuses, squid, and cuttlefish have been consistently on the rise over the last six decades, according to new findings published in Current Biology this week.
Cephalopods boast a unique set of traits that allow them to adapt quickly to changing conditions. They have rapid growth, short lifespans, and flexible physiologies. In fact, some consider them the "weeds of the sea." But the impacts of cephalopod dynamics on marine food webs are hard to predict. Not only are they voracious predators, they’re also a key source of food for many other species, including humans. Cephalopod fisheries are reporting improved catches, for example, but recent observations show declines in giant Australian cuttlefish (pictured above) at their breeding grounds in South Australia’s Spencer Gulf.
To investigate long-term trends in abundance, University of Adelaide’s Zoë Doubleday and colleagues have assembled a global database of cephalopod catch rates – catch per unit of fishing or sampling effort – from 1953 to 2013. They studied 35 different species or genera spanning six cephalopod families living in all major oceanic areas in both hemispheres: 52 percent squid, 31 percent octopuses, and 17 percent cuttlefish and their close relatives, the bobtail squid.
The team found that cephalopod populations are enjoying a global proliferation. Even cuttlefish numbers from South Australia are bouncing back. "The consistency was the biggest surprise," Doubleday says in a statement. "Cephalopods are notoriously variable, and population abundance can fluctuate wildly, both within and among species. The fact that we observed consistent, long-term increases in three diverse groups of cephalopods, which inhabit everything from rock pools to open oceans, is remarkable."
The team is now looking into the factors responsible for this increase. Warmer temperatures are thought to accelerate cephalopod life cycles, for instance, and their populations have also increased in areas where fish have declined due to overfishing.
