Climate crisis affecting rocky seashore species

By Lauren Beavis

Rocky seashore species in Scotland are being affected by the climate crisis due to warming waters, experts say.

An increase in the temperature of Scotland’s seas over the last decade is changing the types of animals and plants found on rocky shores to those that favor warmer waters, a study has found.

The report investigated changes in over 50 species at 167 locations around Scotland’s coasts over the last decade - and found clear evidence of warming in rocky shore communities.

The shift towards warm-water species was shown by an increase of 0.14 degrees Celsius in the average temperature preference of the community.

This comes as a small increase in average sea temperature around Scotland of 0.20 degrees Celsius was recorded.

NatureScot (Scotland's Nature Agency), who published the study, explained whilst these temperature rises 'may seem small, they translate into significant changes in the natural world' - highlighting that climate change is already having an effect on Scotland’s rocky coasts.

NatureScot’s Dr. Kelly James, said: “Scotland’s rocky shores are beautiful, often dramatic, environments teeming with life.

"Our rocky coasts also provide food for many of our birds and animals - as well as ourselves - and help protect our coasts from storms and waves.

"This study highlights that these habitats are already starting to feel the effects of climate change.”

However, the report also revealed that some warm-water species are flourishing - such as the purple topshell, particularly on the west coast of the country.

Cold-water species, on the other hand, are experiencing "mixed fortunes" with some declining, such as beanweed, while others, including cold-water barnacles, are increasing in numbers.

Overall, the study concluded the modest temperature increase has already resulted in a small shift in dominance towards warm water species.

A major finding in the study is the continued ongoing decline of intertidal blue mussels on rocky shores.

Blue mussels are a characteristic species of Scotland’s rocky shores and are an essential source of food for species such as otters, oystercatchers and starfish.

The mollusc has decreased in number across Scotland’s rocky shores, particularly along the southwestern and southeastern coasts.

Healthy populations were only found on exposed outer coasts, such as those on Orkney and Shetland.

This finding aligns with another ongoing study which found declines in blue mussel beds on muddy sediments around Scotland.

While the exact causes of the blue mussel decline remain unclear, factors like marine heatwaves and ocean acidification, both influenced by climate change, are possibly contributing.

Professor Michael Burrows, Scottish Association for Marine Science (SAMS) Marine Ecologist and one of the report authors said: “While the climate-related changes on our seashores over the last ten years or so may seem relatively slow and small, we must remember that climate change is a gradual process and the effects will be really noticeable after several decades.

"Scotland has had a really warm couple of summers recently and further shifts towards warm species since these surveys were completed seem likely.

"Probably the most useful aspect of the study is that it makes a very solid foundation for detecting future change which, given the rate of global warming, seems inevitable.

"Knowing how fast and how much our seashore life is changing tells us a lot about how our seas will continue to support the biodiversity and food we rely on for our continued health and economic prosperity, as well as helping us to better protect the natural world.“

Dr. Kelly James said further monitoring of the impacts of the climate crisis is required

She explained: “Continued, frequent monitoring is needed to further understand these climate change impacts, especially as we have experienced two exceptionally warm years in 2023 and 2024.

"More work is also needed to better understand what these changes to rocky shore communities mean for us, and the other species that depend on them."

"Removing human pressures from rocky shore communities will allow these communities to respond naturally to climate change.

"It is also essential that we reduce emissions and continue the many projects underway, through the Nature Restoration Fund and others, that aim to restore our natural environment, keeping these iconic seascapes safe for future generations.”

The work is part of a larger UK- and Ireland-wide project, the Marine Biodiversity and Climate Change Project - a long-term program tracking changes in rocky intertidal communities in the context of climate change.