‘Weeds of the sea’ are on the rise.
Humans have left their mark on the world’s oceans over the past few decades, altering marine food webs, habitats, and biogeochemical processes. While countless marine species have suffered as a result, evidence suggests that cephalopods — squid, cuttlefish, and octopuses — are proliferating under the same changing environmental conditions.
Zoë Doubleday from the University of Adelaide and her colleagues set out to verify whether the perception that cephalopods are flourishing, fueled largely by increasing cephalopod catches worldwide since the late 1990s, was in fact a reality.
Drawing conclusions from national fisheries data can be tricky, in part because changing factors like the price of fish and cost of fuel can alter the amount of time people spend fishing.
To get a more reliable estimate of long-term trends in cephalopod abundance, the researchers obtained data on the number of cephalopods fishers have caught for a given amount of fishing effort from 1953 to 2013. The study included information on 35 cephalopod species from all over the world.
The data revealed a clear trend: cephalopods are on the rise.
"The consistency was the biggest surprise," said Doubleday in a press release. "Cephalopods are notoriously variable, and population abundance can fluctuate wildly, both within and among species. The fact that we observed consistent, long-term increases in three diverse groups of cephalopods, which inhabit everything from rock pools to open oceans, is remarkable."
The potential ramifications that surging cephalopods will have over time are unclear and are likely to be complex.
"Cephalopods are voracious and adaptable predators and increased predation by cephalopods could impact many prey species, including commercially valuable fish and invertebrates," the researchers wrote in the journal Current Biology.
"Conversely, increases in cephalopod populations could benefit marine predators which are reliant on them for food, as well as human communities reliant on them as a fisheries resource."
Cephalopods are known for their rapid growth, short lifespans, and highly sensitive physiologies, which may allow them to adapt to changing environments more quickly than many other marine species. Nonetheless, the researchers have not yet pinned down precisely why cephalopods are on the rise.
"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 Doubleday.
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