Title:
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Testing hypotheses related to changes in abundance and distribution of warm-temperate invertebrates on rocky shores along the south coast of England
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Surveys of southern invertebrates found on rocky shores along the south coast of England have been carried out since the 1930s. Following exceptionally warm summers in the 1990's, new comparative surveys have been undertaken to determine whether changes have occurred since the last major studies in the late 1970s and early 1980s. Particular attention has been given to the barnacles Chthamalus montagui, C. stellatus and Balanus perforatus, while other species, including the trochid molluscs Gibbula umbilicalis and Osilinus lineatus and limpets Patella depressa and P. ulyssiponensis have been dealt with in less detail. A hypothesis testing approach was then commenced to investigate the various physical and biological constraints on life cycles that might be contributory to the discontinuous distribution of these species along the central south coast of England. Chthamalus montagui and C. stellatus are now found at Bembridge on the Isle of Wight; 8 km and 26 km beyond eastern limits observed in the late 1970's. The abundance of Chthamalus appears to have risen on the south coast of the Isle of Wight subsequent to the last surveys in the 1970's, when densities were observed to have dropped since the 1950's. Balanus perforatus was recorded as far as Eastbourne in Sussex, an eastward extension of 75 km. The topshell Gibbula umbilicalis is still not found east of Bembridge on the Isle of Wight but is now 'common' at Freshwater Bay and 'frequent' at Bembridge, where populations have increased by ten-fold over the past decade.
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