Weeds of the Sea: The Explosion of the Cephalopods

May 26, 2016

What do global warming, overfishing and ocean acidification add up to? Apparently a new dominant species of the underworld – the cephalopod.

In a study published this week in Current Biology, a group of scientists from the University of Adelaide have found, since the 1950’s, the populations of octopus, squid, and cuttlefish have not just risen, everywhere from New England to Japan, they have exploded.

Speculation over why cephalopods have become so successful vary.  Their primary competitors for food have declined as humans have killed off large numbers of other predatory fish.

“It makes sense once you stop and think about how ocean food webs work, but it goes against the conventional wisdom that global fisheries target pretty much everything and, unless well managed, tend to overfish things,” says Benjamin Halpern from the University of California, Santa Barbara in The Atlantic.

Cephalopods may also simply be better at coping with rising ocean temperatures. Certainly part of their success is their rapid ability to adapt. Like rodents, cephalopods have very short life spans, generally 1-2 years and die shortly after the females oversee the hatching of thousands of eggs. As such, they’re referred to as the “Weeds of the Sea” because of their ability to reproduce so rapidly. It’s also believed that warming oceans might be contributing to the acceleration of their birth cycle.

“This is not a sensational ‘cephalopods are taking over the world’s oceans’ story,” says Paul Rodhouse, a biological oceanographer with the British Antarctic Survey in Cambridge, U.K. But the repercussions of a precocious population, especially as they apply to the voracious octopus, could be interesting to watch. These creatures eat 30% of their body weight each day as adults and their foods sources are diminishing at the same time their populations are growing.

However, because they have cannibalistic tendencies, the competition for food resources might just mean they start eating each other and population stabilization is achieved. Either that or humans become more fond of calamari.

“I guess if you’re a squid or octopus fisherman, these increases may seem like a great thing,” says Halpern. “But such dramatic global changes are quite worrisome. When we change the oceans this much, we move things into a new state—one that we know much less about. We might have more squid on our plates in the short run. What are we risking losing in the long run?

To see rare footage of newly-hatched octopus babies captured in the waters of the U.S. Pacific Northwest, go here to view the video.


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