Octopus survivor, Jason Ahrns/Flickr

Overfishing, warming temperatures and increasing acidification threaten many of the animals that live in the ocean. But not charismatic cephalopods. According to a study, published today in Current Biology, octopus, squid and cuttlefish numbers have only increased worldwide.

“Cephalopods are often called ‘weeds of the sea’ as they have a unique set of biological traits, including rapid growth, short lifespans and flexible development,” says lead author Zoë Doubleday of the University of Adelaide. “These allow them to adapt to changing environmental conditions—such as temperature—more quickly than many other marine species, which suggests that they may be benefiting from a changing ocean environment.”

Doubleday and her colleagues actually started looking at global cephalopod data because of the decline of one species. “There has been a lot of concern over declining numbers of the iconic giant Australian cuttlefish at the world-renowned breeding ground in South Australia’s Spencer Gulf,” she says. “To determine if similar patterns were occurring elsewhere, we compiled this global-scale database.”

To investigate long-term trends in abundance, Doubleday and her colleagues assembled global time series of cephalopod catch rates (catch per unit of fishing or sampling effort) from 1953 to 2013. The study included 35 cephalopod species and found that cephalopods of many different types and living all over the world are on the rise. Even the giant Australian cuttlefish is bouncing back.

But why are these invertebrates doing well, when other animals aren’t? “It is a difficult, but important, question to answer, as it may tell us an even bigger story about how human activities are changing the ocean,” Doubleday says.

The authors provide several ideas of why this could be in the new study: “Elevated temperatures… are thought to accelerate the life cycle of cephalopods,” they write. And perhaps the overfishing of their predators is giving cephalopods an edge in the oceans. They also seem to be able to adapt their diets to what is available.

Cephalopods are found in all marine habitats and are an important source of food for many marine species, and humans, too. “As such, the increase in abundance has significant and complex implications for both the marine food web and us,” says Doubleday.

Image: Jason Ahrns/Flickr

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