South American "Red Devil" squid found off Alaska and jellyfish plaguing the Mediterranean may point to vast disruptions in the seas linked to global warming, pollution or over-fishing, experts say.
Fish such as salmon and mackerel have also been spotted in the Arctic, far north of their normal ranges, in a possible vanguard of wrenching billion-dollar shifts in world fish stocks this century caused by warming oceans.
"There will be some places where ocean productivity will increase," said Ron O'Dor, senior scientist of the Census of Marine Life, a 10-year project in more than 70 nations to map the diversity of the oceans.
"The story of global warming is going to be good for some people and bad for others," he added.
Many scientists say that gases emitted by burning fossil fuels coal, gas and oil are blanketing the planet and driving up temperatures, threatening to spur more floods,heatwaves, erosion and rising sea levels.
Warmer oceans are likely to add to older marine threats such as pollution and over-fishing and upset the habitats of everything from crabs and Mediterranean jellyfish to "Red Devil" squid and whales.
As species shift, tropical regions, or almost enclosed seas such as the Mediterranean where fish cannot swim far if the water gets uncomfortably warm, may be among the most vulnerable.
"Areas close to the equator will most likely be the losers while the northern or southern areas might be the winners," said Harald Loeng, head of research in oceanography and climate at the Norwegian Institute of Marine Research.
"It's most likely that some of the species in the North Sea like cod will move north ... and be replaced by anchovies and sardines," he said.