Scandinavian biologists say American and European lobsters are crossbreeding and their offspring can survive in European waters, but it is too early to tell if the hybrids can reproduce.

Susanne Eriksson of the University of Gothenberg in Sweden and Ann-Lisbeth Agnalt of the Institute of Marine Research in Norway presented their findings on the threat that American lobsters found in the northeast Atlantic Ocean pose to their smaller European cousins Tuesday during the second day of the International Conference and Workshop on Lobster Biology & Management in Portland.

“American scientists said your lobsters couldn’t survive in European waters, but we have proof they are not only surviving, but competing with the European lobster for food, shelter and mates,” Eriksson said. “They are crossbreeding, the hybrid eggs are hatching, and the larvae are surviving in our tanks, and in our oceans. We don’t know if they can reproduce yet, that’s a year or two away, but we know the males can produce sperm.”

Last year, Sweden asked the European Union to list the American lobster as an invasive species after scientists there found evidence of crossbreeding. The EU bans the import of invasive species, so a listing would have put an end to the $200 million annual export business. The evidence persuaded the forum of EU scientists who study alien species to support a ban, but not the EU politicians who must approve such a listing.

The EU said it might one day explore other protective measures that would not be so disruptive to trade if Sweden returns with further proof of an invasion.

That’s why Scandinavia is continuing to look at how American-European hybrids will fare in the northeast Atlantic, especially once they hit sexual maturity.


But Eriksson said hybrid weakness could be just as dangerous as above-average strength. If the hybrids are too strong, they could push European lobster populations in Scandinavia into further decline. But if they are too weak, they could dilute the genetic strength of European lobsters through crossbreeding and make the native population susceptible to disease, especially shell disease, which is not found in European lobsters.

There is evidence that the hybrid larvae and juveniles suffer from genetic deformities. Almost a quarter of the crossed larvae have a twisted abdomen, which makes it harder for them to swim, Eriksson and Agnalt found. The deformity also was found in the juvenile hybrids tested in Agnalt’s lab, although it didn’t appear to prevent them from molting or competing for food.

Over the past decade, about 100 American lobsters have been captured in northern Europe – 34 in Sweden, 33 in Norway, 18 in the United Kingdom and four in Ireland. Of those, six female American lobsters have been found carrying hybrid eggs – four in Swedish waters and two in Norwegian waters. These hybrid offspring are the ones that Agnalt and Erikkson have been working with in their labs.

“We are not talking about a lot of lobsters, so you might ask a question: What in heck are you making such a fuss about?” Agnalt said. “But be aware of one important thing. We the scientists are not looking for them. We do not have the same monitoring program in Norway and Sweden like you do here. We depend on the local fishermen, who say something funny is happening here. We think what we are seeing is just the top of the iceberg.”

Even if they can’t produce viable offspring – American scientists have called these hybrid offspring the “mules of the sea” – Eriksson and Agnalt argue that the steady influx of 20 million live lobsters a year into Europe almost guarantees a continuous wave of first-generation hybrids in European waters, due either to accidental releases during transport, cruise ship dumps of not-so-dead lobsters or deliberate free-the-lobster releases.

Each female American lobster that carries hybrid eggs is releasing 6,000 to 11,000 larvae into European waters, Eriksson said. Even if only a small percentage of those survive – in the lab, under controlled conditions, 53 out of 10,700 larvae have survived so far – that is more than enough to weaken the European lobster population through disease and competition, even with just one viable generation, she said.


“I love lobsters,” Eriksson said. “I love the American lobster as much as the European lobster. It’s just the shipping of live lobster that’s a problem. If they were dead when they are shipped, we’d love it. But more than 20 million lobsters a year, that is a lot of lobsters to keep out of our waters. And what we have in our labs is proof that they are getting into our waters, and doing far better than we’d hoped.”

The Scandinavian presentation did not shock University of Maine marine sciences professor Rick Wahle, the conference co-chairman. He said the real evidence of the American lobster’s potential threat will come when Scandinavian scientists find evidence of ovarian formation and viable eggs in female hybrids, and can cross the first generation of hybrids with either parent species, or even each other, successfully.

“There are clearly American lobsters out there, and I agree that the 100 or so they’ve already seen are the tip of the iceberg, but it’s got to be a pretty big iceberg to have an impact on the population,” Wahle said. “There’s no evidence of American lobsters taking off in those waters, like the green crab or Asian shore crab did here. That’s what makes this story stand apart from all the invasive species stories we’ve heard before.”

Penelope Overton can be contacted at 791-6463 or at:

[email protected]

Twitter: PLOvertonPPH

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