Adaptable squid thrive in a changing ocean

Bucking the trend towards declining populations in fish species, the number of cephalopods (octopus, cuttlefish and squid) has increased in the world’s oceans over the past 60 years, a University of Adelaide study has found.

Prompted by concern over declining numbers of the iconic Giant Australian cuttlefish, the research team, led by researchers from the University’s Environment Institute, compiled a global database of cephalopod catch rates to investigate long-term trends in abundance.

The analysis, published in Cell Press journal Current Biology, showed that cephalopod abundance has increased since the 1950s, a result that was remarkably consistent across the three distinct groups.

“Cephalopods are often called ‘weeds of the sea’ as they have a unique set of biological traits, including rapid growth, short life spans and flexible development. 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,” explained lead author Dr Zoë Doubleday, Research Fellow in the Environment Institute and School of Biological Sciences, who said that cuttlefish numbers from the population near Whyalla are now bouncing back.

Project leader Professor Bronwyn Gillanders said large-scale changes to the marine environment, brought about by human activities, may be driving the global increase in cephalopods.

“Cephalopods are an ecologically and commercially important group of invertebrates that are highly sensitive to changes in the environment,” Professor 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, as well as being voracious predators, they are also an important source of food for many marine species, as well as humans.

“As such, the increase in abundance has significant and complex implications for both the marine food web and us,” said Dr Doubleday.

Image caption: Giant Australian cuttlefish (Sepia apama), Spencer Gulf, South Australia. Image credit: David Wiltshire.