Scientists complete largest global assessment of ocean warming impacts

Scientists have compiled the most comprehensive assessment to date of how ocean warming is affecting the mix of marine species in our oceans – and explain how some species manage to keep their cool.

Turtle surfacing Credit: Mark Costello

Researchers from the UK, Japan, Australia, USA, Germany, Canada, South Africa and New Zealand analysed three million records of thousands of species from 200 ecological communities across the globe.

Reviewing data from 1985 – 2014, the team, led by Professor Michael Burrows of the Scottish Association for Marine Science (SAMS), showed how subtle changes in the movement of species that prefer cold-water or warm-water, in response to rising temperatures, made a big impact on the global picture.

The findings, published in the journal Nature Climate Change, show how entire communities change as warm-water species increase and cold-water marine species become less successful due to climate warming.

However, the study also found evidence that some cold-water species will continue to thrive by seeking refuge in cooler, deeper water when the surface waters are too hot. However, not all animals may have this opportunity either because they cannot move or there is no cool deep water where they live.

Professor Burrows said the global picture showed what scientists had suspected of happening.

“Changes in the composition of ocean communities exactly reflect ocean warming. However, within these communities are subtle changes that make a huge, and previously unknown, difference to the bigger picture.”

The study looked at data from the Northern Hemisphere including the North Atlantic, Western Europe, Newfoundland and the Labrador Sea, east coast USA, the Gulf of Mexico, and the North Pacific from California to Alaska with the North Atlantic showing the largest rise in average temperature during the time period.

However, for fish communities in the Labrador Sea, where the temperature at 100 metres deep can be as much as five degrees Celsius cooler than the surface, moving deeper in the water column allowed cold-water species to remain successful.

Most of the data was collected via targeted surveys of commercial fish stocks, but also associated seabed species and the plankton that comprise their food. Thus the changes seen reflect those likely to be seen in fish markets as cold-water fish like cod and haddock decline while warm-water species like red mullet increase with warming.

There has been a temperature rise of almost one degree Celsius in some parts of the ocean since 1985, a significant change in just three decades.

Professor Mark Costello from the University of Auckland’s School of Environment who co-authored the research paper, says it validates previous projections about the rapid responses of marine life to ocean warming.

Professor Mark Costello

While the study focused on the North Atlantic and North Pacific where warming has been most pronounced, given time, similar changes in ecosystems will occur elsewhere in the world if warming continues, he says, including New Zealand.

However to date, temperatures have not changed as much around New Zealand although there is almost no regular sampling of marine biodiversity that would detect such changes.

The study analysed data published online in the Ocean Biogeographic Information System (OBIS) which contains a lot of data from New Zealand but as yet does not have sufficient data to allow tracking of climate change effects from year to year. Professor Costello led the development of OBIS for its first eight years.

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