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The end of the cold war: understanding the tide of change on the rocky shore

How climate change is affecting competition for space among northern and southern species

Climate change affects marine organisms in two distinct ways: their success in coping with their physical environment, and how they interact with each other.  Michael Burrows and Elvira Poloczanska* from SAMS, together with Steve Hawkins and the late Alan Southward at the Marine Biological Association in Plymouth, have recently published a series of models of changes in abundance of southern and northern species of barnacles from the 1950s to the 1980s. Alan Southward's yearly counts at sites around southwestern UK shores showed that the barnacles closely followed year-to-year changes in spring sea temperatures.

Barnacles by M Burrows SAMSThe new study shows that two important processes are needed to explain the changes: Warm temperatures reduce the successful settlement of the larvae of the cold water species Semibalanus balanoides (=white in the image). This in turn reduces the impact of the northern species on the two southern species, Chthamalus montagui (=light brown in the image) and Chthamalus stellatus, in a contest that the northern form usually wins.

Counts of barnacles since the 1980s show that southern species has continued to dominate through the current warm period, and is likely to eventually replace the northern species altogether. The models show that temperatures projected for the 21st century will mean the end of the cold war for the northern barnacles in the south of Britain.

An appreciation of Alan Southward's life and contribution to marine science can be found here. We are pleased to dedicate the paper to Alan.

The paper can be found here. The study was supported by NERC through a small grant, the SAMS Northern Seas Programme, and Oceans 2025 Theme 4 Biodiversity and Ecosystem Functioning.

* Elvira is now at CSIRO in Hobart, Tasmania

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