Unlike the declining populations of many fish species, the number of cephalopods - octopus, cuttlefish and squid - has increased in the world's oceans over the past 60 years, a new study has found.
The international team, led by researchers from University of Adelaide in Australia, compiled a global database of cephalopod catch rates to investigate long-term trends in abundance.
"Our analyses showed that cephalopod abundance has increased since the 1950s, a result that was remarkably consistent across three distinct groups," said Zoe Doubleday, Research Fellow in the Environment Institute and School of Biological Sciences.
"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," said Doubleday.
"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," Doubleday said.
Doubleday said the research stemmed from an investigation of declining numbers of the iconic Giant Australian cuttlefish. "Surprisingly, analyses revealed that cephalopods, as a whole, are in fact increasing; and since this study, cuttlefish numbers from this iconic population near Whyalla are luckily bouncing back," Doubleday said.
Project leader 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," 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," said Gillanders.
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," Doubleday added.
The study was published in the journal Current Biology.