IT does not seem like much, but the world’s seas have warmed by an undramatic-sounding one per cent since the middle of the 1980s.

But a new and detailed study has revealed that this heating has already had a profound impact on ocean life – including species many of us eat.

An international group of marine scientists – including Scots – has compiled the most comprehensive assessment yet of how warming is affecting the mix of species in our oceans.

The findings – including explaining how some fish manage to keep their cool in hotter waters – come on the same day as another major international study concluded CO2 levels in the atmosphere continued to rise last year.

Reviewing data from 1985 to 2014, the team led by Prof Michael Burrows of the Scottish Association for Marine Science (SAMS) in Oban showed how subtle changes in the movement of species that prefer cold-water or warm-water, in response to rising temperatures, could have a remarkable planet-wide impact.

Prof Burrows said: “The global picture shows what we suspected was happening: changes in the composition of communities exactly reflect ocean warming.

“However, within these communities are subtle changes that make a huge, and previously unknown, difference to the bigger picture.”

His team, including 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.

The findings, published in the journal Nature Climate Change, show how warm-water species increase and cold-water marine species become less successful as the global temperature rises.

These fluctuations are incredibly important for ecosystems, including Scotland’s.

Last month scientists at Marine Scotland, the Scottish Government’s fisheries protection quango, yesterday published research getting underneath the effects of global heating on the predators and prey.

They focused on the future of sandeels, the tiny fish that are the favourite food of puffins.

Sandeel larvae usually hatch close to the start of a “bloom” in their prey, the eggs of tiny crustaceans called copepods. Changes in water temperature means the birth of sandeels and copepods are out of kilter. And that means hungry puffins.

However Prof Burrows’ study also suggests that some cold-water species will continue to thrive by seeking refuge in cooler, deeper water. They are swimming down, rather than north, in an attempt to cool off.

The truly global study looked at data from 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. While the global warming trend was widely seen, the North Atlantic showed 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 the cold-water species to remain successful.

Prof Burrows added: “From 1985 to 2014 we conducted the equivalent of an electoral poll in the ocean, showing swings between types of fish and plankton normally associated with either cold or warm habitats. As species increase in number and move into,

or decline and leave, a particular ecological community, the make-up of that community will change in a predictable way.

“Most of the data collected were targeted surveys of commercial fish stocks, so 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.”

The temperature rise of almost one degree Celsius in some parts of the ocean since 1985 is a significant change in just three decades, says Prof Burrows.

“While this may not sound like a big change, it has a considerable impact on species that may already be on, or close to, their maximum temperature tolerance.

“A gradual temperature change like the one we are witnessing is not going to cause extinctions overnight but it is affecting the success of many species, not least zooplankton such as copepods, which are crucial to the ocean food web.”

Warming oceans are also linked to a rise in the intensity and number of tropical storms.