Some 150,000 baby common octopuses (Octopus vulgaris) have just been released into the waters off Italy’s Adriatic coast in one of Europe’s first pilot experiments to test whether the species can help control the invasive blue crab (Callinectes sapidus), which eats native shellfish and threatens the fishing industry and marine ecosystems.
“The project is appropriate as a carefully controlled pilot experiment, but it is not yet a proven effective control strategy,” says Rom Lipcius, a marine ecologist at the Virginia Institute of Marine Science, who isn’t involved in the initiative.
Two years ago, Oliviero Mordenti and Antonio Casalini, two aquaculture researchers at the University of Bologna, Italy, began to wonder whether octopuses offered a way to control blue crabs off the coast of Emilia-Romagna, a region of north-east Italy where damage caused by the blue crabs has cost the fishing industry £14.7 million since 2022.
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Previous studies had identified the common octopus as a predator of the blue crab, backing up what local fishers had been seeing for a decade as populations of the Atlantic-native invasive species began to surge along Italian coasts.
However, octopuses tend to do better on rocky seabeds, while the Adriatic coast is rather sandy, which may help explain why octopus numbers there have been falling in recent decades. The regional government of Emilia-Romagna has installed artificial shelters for octopuses in an effort to reverse the decline.
Under a research project co-financed by the regional government, Mordenti and Casalini caught eight common octopuses – four females and four males – from the Emilia-Romagna coast, transferred them to the laboratory and gave them about three months to acclimatise to their new surroundings. Their tanks were carefully monitored and maintained under conditions designed to simulate those at sea. “Not only did we find that the fishermen were right, but we also found that octopuses could consume up to four blue crabs a day,” says Mordenti.
The researchers then arranged the octopuses into four breeding pairs and allowed them to mate and produce eggs.
Earlier this week, the scientists released 150,000 millimetre-long, lab-raised larvae into the waters off the coastal towns of Cesenatico and Riccione.
They estimate that only 1 per cent will survive to adulthood. After hatching, octopuses start their lives as tiny, free-floating larvae known as paralarvae. They drift through the water and may be eaten by fish. The hope is that a few will escape this fate and grow large enough to begin preying on blue crabs — a feat even small common octopuses weighing less than 800 grams are capable of, the researchers say.
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“Our aim was to bolster the population of a native species already found naturally in the Adriatic,” says Casalini.
“We’ll work with fishermen to assess whether the releases will have had an effect by the end of the year,” says Mordenti.
But some scientists argue that this strategy needs more study. “Blue crabs are extremely prolific and fast‑growing, and their preferred habitats often differ from those of octopuses,” says marine biologist Jorge Hernández-Urcera at the Institute of Marine Research, Spain.
“Starting by releasing paralarvae as if they were wheat seeds scattered in the water seems like a rather simplistic approach,” says Anna Di Cosmo, a zoologist at the University of Naples Federico II, Italy. “A controlled environment is one thing; the open sea is a whole different ball game.”