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What will extra cephalopods mean for marine ecosystems?

Octopus vulgaris resting on a reef. This mollusc can be found in the Mediterranean Sea and in the Atlantic Ocean Octopus vulgaris resting on a reef. This mollusc can be found in the Mediterranean Sea and in the Atlantic Ocean MattiaATH/Shutterstock
03 Jun
A delicious opportunity or proof of human impact on the ocean? The news of booming cephalopods (octopuses, cuttlefish and squid) has already divided seafood lovers and environmentalists. Whatever your opinion, cephalopods appear to be thriving while other marine species flounder, raising questions about the state of underwater ecosystems

A recent study published in Current Biology shows that cephalopod numbers have increased over the last six decades. By analysing numbers of cephalopods caught as bycatch in fishing vessels, researcher Zoë Doubleday of the University of Adelaide’s Environmental Institute, observed population rises all over the world. ‘Cephalopods are notoriously variable, and population abundance can fluctuate wildly, both within and among species,’ she says. ‘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.’

oie 6froxBbBE57EOctopus numbers are on the increase (Image: Kerry L Werry)

Cephalopods are flexible, both physically and ecologically. They have rapid growth and relatively short lifespans, leading scientists to speculate that they can keep up with the changes to their environment, especially warming oceans. In fact, warmer waters are thought to accelerate their life cycles, so long as it does not surpass their tolerance and food is not limited. Cephalopods may also be less at risk from predators, thanks to the global depletion of fish stocks. ‘It is relatively well documented that many fish species have declined in abundance due to overfishing,’ they write, ‘and several regional studies have suggested that cephalopod populations have increased where local fish populations have declined.’

Because they occupy the middle of the food chain, a boom in cephalopods will undoubtedly have an impact on marine ecosystems. ‘All cephalopods are carnivores and they eat lots of different types of prey including fish, other molluscs, and crustaceans,’ says Doubleday, ‘so it may reduce those animals. However, they are also an important source of food for many animals including seals, whales, predatory fish and sharks, and seabirds.’ She is wary, however, that their increase will go unchallenged for long, ‘they are becoming an ever-more important component in global fisheries, and feature increasingly on menus, so we might eat them before they increase too much.’

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