Sea creatures known as ‘weeds of the sea’ are a growing population

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A giant Australian cuttlefish is among growing population of cephalopods. Photo: Courtesy of David Wiltshire

Amid concern about the dwindling populations of sharks and pelagic fish, a certain set of sea creatures known as “weeds of the sea” are actually enjoying a prolonged growth spurt in their worldwide populations.

The number of cephalopods — octopus, cuttlefish and squid — has increased in the world’s oceans since the 1950s, a University of Adelaide study has found, as reported by The Christian Science Monitor and The Guardian.

“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,” lead author Dr. Zoë Doubleday, Research Fellow in the Environment Institute and School of Biological Sciences, said in a press release. “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.”

An international team of researchers led by those from the university’s Environmental Institute compiled a global database of cephalopod catch rates to determine long-term trends in abundance and the results were published in the journal Current Biology.

Sea creatures known as cuttlefish join octopuses and squid in prolonged growth spurt.Sea creatures known as cuttlefish join octopuses and squid in prolonged growth spurt. Photo: Courtesy of Scott Portelli Wildlife Photographer

“It is certainly nice to see something going up [in numbers],” Doubleday told The Christian Science Monitor, which added that there might be a downside to this expansion.

“From a squid’s perspective, it is good news … [but] maybe not from a fish’s perspective,” Michael Vecchione of NOAA Fisheries Systematics Laboratory told The Christian Science Monitor.

“They have a high metabolic rate, high growth rate and as a result they have a high requirement for food. So they eat a lot of stuff. If there are a lot of squids out there eating juvenile fishes, it could make it more difficult for the fish populations to recover.”

Doubleday countered by saying cephalopods are also food sources for marine animals, birds and humans, and so balance might return to the food chain over time, as “nature has a way of self-regulating.”

If the growing population eventually finds there isn’t enough food to support it, the cephalopods “might self-regulate by eating each other,” Doubleday said. “They might crash just as much as they’ve increased.”

Professor Bronwyn Gillanders, the project leader, said cephalopods are an ecologically and commercially important group of invertebrates that are highly sensitive to changes in the environment.

“We’re currently investigating what may be causing them to proliferate — global warming and over-fishing of fish species are two theories,” Gillanders said. “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.”

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