A new study shows that the combined effects of warming and predation could lead to more widespread marine biodiversity loss than are currently predicted, as animals or plants are unable to shift their habitat ranges.

The study by University of Columbia zoologist Christopher Harley, examined the response of barnacles and mussels to the warming and predation by sea stars.

"Rocky intertidal communities are ideal test-beds for studying the effects of climatic warming," says Harley, an associate professor of zoology at UBC and author of the study. "Many intertidal organisms, like mussels, already live very close to their thermal tolerance limits, so the impacts can be easily studied."

The study found that at cooler locations, mussels and rocky shore barnacles were able to live high on the shore, beyond the range of their predators. But with higher temperature, these creatures were forced to live at lower shore levels, at the same level as predatory sea stars.

In the last 60 years, summer temperatures increased by almost 3.5 degrees Celsius, causing the upper limits of barnacle and mussels habitats to retreat by 50 centimeters down the shore, contrary to its effect on predators which has remained constant.

"That loss represents 51 per cent of the mussel bed. Some mussels have even gone extinct locally at three of the sites I surveyed," says Harley. On the other hand, when pressure from sea star predation was reduced using exclusion cages, these were able to move to warmer sites and the species richness at the sites more than doubled.

"Warming is not just having direct effects on individual species," says Harley. "This study shows that climate change can also alter interactions between species, and produce unexpected changes in where species can live, their community structure, and their diversity."

The study was published in the current issue of the journal Science.