Recent changes in abundance of intertidal barnacles in south-west England: A possible effect of climatic deterioration
Southward, A.J. (1967) Recent changes in abundance of intertidal barnacles in south-west England: A possible effect of climatic deterioration. Journal of the Marine Biological Association of the United Kingdom, 47 (1). pp. 81-95.
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Annual surveys carried out in south-west England since 1949 show that the arctic-boreal barnacle, Balanus balanoides, which was uncommon or rare in 1960, has increased greatly in abundance during the colder years since then. Its numbers now approach those recorded in the 1930'S, and there has been a corresponding reduction in abundance of the warm-water species, Chthamalus stellatus. Detailed analysis of records for South Devon indicates a 2-year phase-lag between changes in sea temperature and corresponding fluctuations in the barnacle populations, warm periods being followed by increases in Chthamalus,cold periods by increases in B. balanoides. It appears that a direct effect of temperaturecan be discounted, and that exceptional cold spells, such as the winter of 1962-63, by themselves are not of great importance. The evidence supports previous views that the distribution and abundance of the two species is broadlycontrolled by temperature acting on competition between them. Other habitats have also shown increases in cold-water species and decreases in warm-water species, herring and pilchard being notable examples among fishes. Increases in warm-water species between the 1930'S and the early 1950'S have been linked with the general climatic amelioration from 1900 to 1950, and the recent changes seem to be part of a reverse trend associated with deterioration in climate. On the land this deterioration seems to have set in during the 1940'S,but in the sea it would appear to have begun some 10 years later.
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