C .J. Jeffery, A.J. Underwood J. Exp. Mar. Biol. Ecol. 256 2001 85 –97
89
extrapolating down to the x-axis from where each graph line first decreased in slope see Fig. 5. A correlation between periods of growth and size of adults at each site was then
calculated. To test hypotheses derived from model 3, 15 small 1–2 mm barnacles were
randomly selected at each site and were traced from maps of replicates from 1989 to 1992. The number of years that each of these barnacles survived longevity was
recorded. Correlations were then calculated between mean number of years that these barnacles survived and mean size of 30 adults
. 1 mm randomly selected from six sites. Also, the percentage of older barnacles
. 3 years of age in 10 places in areas where barnacles were relatively large was compared with 10 places in those areas where
barnacles were relatively small. Annual rates of growth were calculated as: R
5 logL L t where R, rate of growth;
t
L , aperture-length at time t; L , aperture-length at time zero; and t, time in years see
t
Denley and Underwood, 1979; Underwood, 1984.
3. Results
3.1. Size Aperture-length was positively correlated with shell-length Fig. 1 indicating that
aperture-length is a good estimator of size and growth in this species. The largest barnacles were found at exposed Site 6 and the smallest at sheltered Site 3. Barnacles
were generally larger on mid and upper heights at Cape Banks Fig. 2; Tables 2 and 3. Size differences were recorded among sets of replicates on semi-exposed Site 5 and
exposed Sites 1, 2 and 6 see Table 1.
3.2. Growth When correlations were calculated on b the slope of regression from Fig. 3 and
between mean size of adults .1 mm at each site, no significant relationship was found
Fig. 4a and Spearman’s rank correlation, r 5 20.2, P50.35. Nor was there a
significant correlation between annual growth-rates of juveniles first measured in 1989 and later in 1992 and mean size of adults at each site Fig. 4b and Spearman’s rank
correlation, r 50.37, P50.23.
When juveniles ,1 mm were first measured at the end of 1989 and individuals of
the same cohort were measured at the end of each year up to the end of 1992 so that periods of growth years at each site could be estimated see Fig. 5, periods of growth
were found not to vary among sites Fig. 4c and Spearman’s rank correlation, r 5 20.34,
P 50.26.
There was a relationship between years surviving longevity of small 1–2 mm barnacles and mean size of adults at each site, although not statistically significant Fig.
4d and Spearman’s rank correlation, r 50.66, P50.08. That is, where barnacles were
larger, longevity was also greater. When percentages of old barnacles .3 years of age
90 C
.J. Jeffery, A.J. Underwood J. Exp. Mar. Biol. Ecol. 256 2001 85 –97
Fig. 1. Relationship of shell-length mm and aperture-length mm of Chamaesipho at six sites. Correlations were calculated separately for each site on pooled raw data from 10 barnacles randomly sampled from black
and white negatives photographed in October, 1989 on low, mid and upper heights at each site.
recorded at the end of 1992 were compared in areas predominated by large and small barnacles, respectively, a greater mean percentage of older barnacles
.3 years of age was found in areas predominated by large barnacles 60.36; S.E.
54.04 than in areas with mainly small barnacles 19.27; S.E.
53.45. These results indicate that longevity varies among areas at Cape Banks and that increased longevity of juveniles through
adulthood in some areas will determine that larger barnacles will predominate in these areas.
C .J. Jeffery, A.J. Underwood J. Exp. Mar. Biol. Ecol. 256 2001 85 –97
91
Fig. 2. Size-frequency distributions of Chamaesipho measured in three replicates on low, mid and upper heights at Sites 3, 6 and 2, respectively, in late 1989 and again in late 1992.
4. Discussion
