When dead sea mammals started washing ashore on Canada’s west coast in greater numbers, marine biologist Andrew Trites was distressed to find that domestic animal diseases were killing them.

There are dramatic shifts in the ocean ecosystem

Around the world seals, otters and other species are increasingly infected by parasites and other diseases long common in goats, cows, cats and dogs, marine mammal experts told a major science conference.

The diseases also increasingly threaten people who use the oceans for recreation, work or a source of seafood, scientists told reporters at the annual meeting of the American Association for the Advancement of Science.

The symposium Swimming in Sick Seas was one of many sessions at this year’s AAAS that drew a bleak picture of the state of the world’s oceans, which are increasingly acidic, warming in some areas and being inundated with melting ice or other climate change effects.

“There are dramatic shifts in the ocean ecosystem,” said Jason Hall-Spencer of Britain’s University of Plymouth, citing his research in Italy, Baha California and Papua New Guinea that is “all showing the same thing” – with an increase in carbon dioxide, “you get a 30 per cent drop in microbes, plants and animals” in the oceans.

Gretchen Hofmann of the University of California at Santa Barbara said increasing ocean acidity, caused by CO2 from fossil-fuel burning, is killing shellfish young – called spat – worldwide.

In the Pacific Northwest of Canada and the US, the failure of spat hatcheries threaten a commercial industry worth more than $200 million, said Ms Hofmann.

Lisa Levin of the Scripps Institution of Oceanography in La Jolla, California, said warming of the water reduces how much oxygen it can hold, newly threatening deep-sea creatures that have survived for millennium under stable conditions.

“There are undoubtedly organisms down there that can be very beneficial to us, that we have yet to find,” Ms Levin said.

According to Mr Trites, director of the Marine Mammal Research Unit in at the Fisheries Centre at University of British Columbia, the bodies washing ashore are a grim signal.

“I see the dead mammals coming ashore as canaries in a coal mine,” said Mr Trites.

Parasites, funguses, viruses and bacteria are increasingly passed from land to sea animals because human settlements on coastlines changes water patterns through paving, filling of wetlands that are natural filters, and intensive agriculture run-off, said scientists.

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