Squid, octopus and cuttlefish are on the rise, finds new research on these animals, which are collectively known as cephalopods.
Nicknamed the "weeds of the sea," these animals have experienced impressive population growth over the past 60 years and at a time when many fish species have been declining in numbers, according to the new study, which is published in the journal Current Biology.
"Our analyses showed that cephalopod abundance has increased since the 1950s, a result that was remarkably consistent across three distinct groups," lead author Zoë Doubleday, a researcher at the University of Adelaide's Environment Institute and School of Biological Sciences, said in a press release.
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"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," Doubleday continued. "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."
What sparked the research was an observed decline of a species that's iconic down under: the giant Australian cuttlefish.
Doubleday explained that researchers started to notice fewer of these cuttlefish at the cephalopod's world-renowned breeding ground in South Australia's Spencer Gulf.
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The scientists compiled a global-scale database of cuttlefish, as well as squid and octopus. Not only did the study reveal that the giant Australian cuttlefish is already making a major comeback, but also that most other related animals have been increasing in numbers over the past six decades.
Like weeds taking over a garden, however, the news isn't all good.
Co-author Bronwyn Gillanders said large-scale changes to the marine environment, brought about by human activities, could be driving the global increase in cephalopods.
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"Cephalopods are an ecologically and commercially important group of invertebrates that are highly sensitive to changes in the environment," Gillanders said. "We're currently investigating what may be causing them to proliferate - global warming and overfishing of fish species are two theories. 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."
Cephalopods are found in all marine habitats and are voracious predators. On the flip side, they are an important source of food for many marine species, as well as people.
This means, Doubleday says, "the increase in abundance has significant and complex implications for both the marine food web and us."