The ocean is changing. Or rather, we are changing the ocean in more ways than many of the marine inhabitants can handle. Rising temperatures and ocean acidification is devastating coral and killing off dependent marine life. There is one group, however, that seems to be adapting to these harsh conditions. Out of the emerging ocean desert comes a team of cephalopods, who are ready to overpower the existing marine life hierarchy. Or are they? We investigate into the latest claim that cephalopods are taking over the oceans.

Cephalopods are a class of mollusc, which scientists classify as octopuses, squid, cuttlefish and nautiluses. Greek for “head-footed”, there are believed to be over 700 hundred of the species and they inhabit all of the world’s oceans, from its shallow coral reefs to its deepest darkest points. They grow quickly but have short life spans, and some types – mainly octopus – have been known to display a high level of intelligence. These alien-like, three-hearted creatures are believed to be taking over the ocean.

Professor Bronwyn Gillanders, of the Southern Seas Ecology Laboratories, explains the traits that cephalopods have that allows them to adapt to these changing oceans: “Cephalopods are generally highly responsive to environmental change. For example with increasing temperature they accelerate their growth rate provided the temperature increase is within their thermal tolerance and there is sufficient food. The short life cycle (1-2 years) may offer a competitive advantage over longer-lived, slower growing taxa. Key traits are extreme life history plasticity, continuous rapid growth and short life spans.”

Another theory on why the environmental conditions for cephalopods might have improved is that humans are picking off their main competitors–predatory fish. It is a variety of factors that is currently giving cephalopods the edge over other marine life.

A broadclub cuttlefish, the largest of the tropical cuttlefishes. ©

A broadclub cuttlefish, the largest of the tropical cuttlefishes. ©

To come to this conclusion that cephalopods were on the rise, researchers analysed the rate at which cephalopods have shown up in fishing catches or sampling efforts, spanning all major ocean regions, from 1953 to 2013. “Our research focused on looking at catch per unit effort data as a proxy for the abundance of cephalopods.” Bronwyn explained.

“We gathered as many datasets as possible for different species around the world, with a focus on longer term datasets (>10 years). Some data came from Japanese and Spanish language publications. The species investigated ranged from large scale squid fisheries, such as those occurring around the Falkland Islands, to subsistence fisheries (e.g. Octopus in Madagascar). Looking at the data based on collection type (e.g. Fisheries vs non-fisheries data) and life history (e.g. Different types of dispersal and living in different parts of the ocean) we found that all consistently increase in abundance through time.”

This increase in cephalopods could benefit their predators, such as sperm whales and sea lions, but could potentially be extremely harmful to their prey, as cephalopods are known to be voracious hunters. But for now, it is too early to predict whether cephalopod population will continue to boom, and what this means exactly for the future of the oceans, and its life, remains unclear. As humans continue to tamper and experiment with the world below the waves, unintentionally driving many marine animals to extinction, the unquenchable cephalopods continue to thrive.

But Bronwyn does add: “[that] at the end of the day, if there is nothing else to feed on, they are likely to just eat each other.” 

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