The small honeycomb barnacle Chamaesipho tasmanica Foster and Anderson often forms
continuous sheets covering the substratum at mid-shore levels of sheltered rocky shores but also
occurs in sparse distributions on exposed shores, and on higher levels of sheltered shores, in
south-eastern Australia. Larger barnacles are generally found in more exposed and higher areas.
Effects of each site on ultimate sizes of barnacles were therefore examined by measuring growth
of barnacles of the same cohort at sheltered and exposed shores from the end of 1989 to the end of
1992. Because Chamaesipho varied in size among sites, and because size was not necessarily
representative of age, three growth models were proposed to explain this size differential. While
rates of growth and periods of growth did not differ, differences in longevity were found to
influence size so that larger barnacles survived longer and were more abundant on the more
exposed shores. In fact, when barnacles were aged, it was found that a greater proportion of older
barnacles (.3 years of age) occupied these exposed areas. It seems that site-specific characteristics
influenced longevity in some places so that larger Chamaesipho continued to predominate in
these areas. Crown copyright Ó 2001 Published by Elsevier Science B.V. All rights reserved