Considerable variation in distribution and abundance of populations of the small
honeycomb barnacle Chamaesipho tasmanica exists from place to place at the Cape
Banks Scientific Marine Research Area (Sydney, Australia); small patches of larger
barnacles often inhabit exposed areas, and higher levels of sheltered shores, whereas
large numbers of smaller barnacles carpet the mid-littoral substratum on sheltered
shores. It may be, therefore, that larger barnacles are generally found on these upper and
more exposed shores because growth is fastest here. Apart from faster growth, adults
may be of different sizes in different areas because they grow for longer periods or
because they survive longer in some areas. Three models were therefore proposed to
explain the differences in size of adult Chamaesipho in different sites at Cape Banks.
The first model is that barnacles may grow faster at some sites — therefore finishing
growth at a larger size in these areas. It was predicted that, if the same cohort of
barnacles were measured from juvenile (,1 mm) to adult sizes, rate of growth of these
juveniles in different areas should be correlated with the sizes of adults in these areas.
The second model proposed that barnacles grow at the same rate, but have longer
periods of growth in some areas. It was predicted that, if juveniles from the same cohort
were measured from settlement, the periods during which barnacles in different areas
grew should be correlated with sizes of adults in these areas. The third model is that
barnacles keep growing, but live longer at some sites. Therefore, if juveniles from the
same cohort were measured there should be a correlation between longevity of these
juveniles and size of adults. Greater longevity will be recorded in areas where barnacles
are relatively large.