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.J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26
Short and Trenaman, 1992, which contribute to conditions of variable exposure. Tides are semi-diurnal and range over 2 m.
2.2. Influence of substrate availability and conspecific adults on gregarious settlement
In July 1991 and 1992, 6, 3 and 1.5 cm diameter patches n 5 3 were cleared on the
substratum within aggregations of barnacles at Sites 3 and 4 at each Low, Mid and Upper height of Chamaesipho’s distribution. From July to December each year, in 1991
and 1992, settlers were removed daily from each different-sized patch for approximately 6 days during each new and full moon. Very few, if any, barnacles settled during the
intervening period Jeffery, 1997. Daily removal was necessary to negate possible confounding by gregariousness as neighbouring settlers aged Jeffery, 1997, and to
ensure that only free space and conspecific adults on perimeters could act as cues for settlement. Numbers of barnacles settling in these patches were recorded until December
of each year of the experiment.
Total numbers of settlers in the patches in each experiment in 1991 and 1992 were compared. Because different-sized patches were used in this investigation it was
necessary to separate the influences of the availability of substratum and numbers of adults along perimeters of patches. Numbers of larvae settling on different-sized patches
were manipulated in two ways. To test the hypothesis that amount of available free space will influence settlement, the total numbers of settlers recorded each year on plots
where larvae were removed daily were divided by the appropriate areas 28.28, 7.07 and
2
1.77 cm . To test the hypothesis that larval choice will influence settlement near conspecific adults, the numbers of barnacles settling were divided by the appropriate
perimeters 18.85, 9.43 and 4.71 cm.
3. Results
3.1. Total numbers of settlers Where settlers were removed from patches from July to December 1991 and 1992,
total numbers of settlers were always greater in 6 cm patches than in 3 cm patches, which had more than 1.5 cm patches Fig. 1. In 1991 there were generally more settlers
at Site 3 than Site 4. More settlers were always recorded at Low heights and there was a decrease in numbers of settlers as patch size decreased 6 cm
.3 cm.1.5 cm; Fig. 1; Table 1a.
3.2. Availability of substratum When total numbers of settlers were divided by areas of 6, 3 and 1.5 cm patches, more
settlers were recorded in the smallest 1.5 cm patches in 1991 at Site 3. While greater numbers of settlers were recorded in 1.5 and 3 cm patches at Low heights than at Mid
and Upper heights, there was no significant difference in settlers among heights in 6 cm
C .J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26
19
Fig. 1. Mean total annual numbers of barnacles settling in patches n 5 3 of different size 6, 3 and 1.5 cm at
Sites 3 and 4 on Low, Mid and Upper heights of Chamaesipho’s distribution in December, 1991 and 1992. Note different scale on y-axis among sites and heights.
patches. There was some variation in settlement among heights on the shore: at Low heights there was a progressive decrease in total numbers of settlers as patch size
increased 1.5 cm .3 cm.6 cm; at Mid heights most settlement also occurred in
smallest patches, although there was no difference between the intermediate and largest sized patch 1.5 cm
.3 cm56 cm; and at Upper heights, while there was no significant difference in settlement among the different-sized patches, settlement increased as patch
size decreased 1.5 cm 53 cm56 cm; Fig. 2; Table 1b. These results suggest that
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.J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26 Table 1
Analysis of total annual numbers of barnacles settling in 6, 3 and 1.5 cm patches on which settlers were removed daily n
5 3 at Sites 3 and 4 on Low, Mid and Upper heights of Chamaesipho’s distribution. Experiments were renewed each year and data are totals in December in 1991 and 1992: a total numbers of
settlers in different-sized patches; b total numbers of settlers unit area of patch availability of substratum;
a
c total numbers of settlers unit perimeter of patch adults at perimeters
Source df
MS F
P a Total numbers of settlers analysis of variance,
0.5
data transformed x 1 1 ; Cochran’s test, P . 0.05
Time: T 1
631.96 188.65
Site: S 1
9.83 7.42
Height: H 2
115.80 15.99
ns Patch size: P
2 61.05
118.79 T
3S 1
3.35 2.53
ns T
3H 2
26.96 1.43
ns T
3P 2
17.38 17.70
ns S
3H 2
7.24 5.46
S 3P
2 0.51
0.39 ns
H 3P
4 5.20
6.00 ns
T 3S3H
2 18.92
14.27 T
3S3P 2
0.98 0.74
ns T
3H3P 4
1.69 3.14
ns S
3H3P 4
0.87 0.65
ns T
3S3H3P 4
0.54 0.41
ns Residual
72 1.33
b Availability of substratum analysis of variance, data untransformed; Cochran’s test, C
5 0.51, P , 0.01 Time: T
1 2211.46
5333.31 Site: S
1 11.96
0.56 ns
Height: H 2
613.65 18.23
ns Patch size: P
2 828.57
590.25 T
3S 1
0.41 0.02
ns T
3H 2
290.61 3.28
ns T
3P 2
460.62 278.54
S 3H
2 33.67
1.57 ns
S 3P
2 1.40
0.07 ns
H 3P
4 149.32
11.32 T
3S3H 2
88.48 4.14
T 3S3P
2 1.65
0.08 ns
T 3H3P
4 54.25
1.47 ns
S 3H3P
4 13.19
0.62 ns
T 3S3H3P
4 36.97
1.73 ns
Residual 72
21.38 c Adults at perimeters analysis of variance, data
transformed log x 1 1; Cochran’s test, P . 0.05
e
Time: T 1
48.14 189.00
Site: S 1
0.94 10.02
Height: H 2
7.56 12.91
ns Patch size: P
2 0.40
32.92 T
3S 1
0.25 2.70
ns T
3H 2
0.97 0.58
ns T
3P 2
0.05 1.43
ns S
3H 2
0.59 6.22
S 3P
2 0.01
0.13 ns
H 3P
4 0.15
3.41 ns
T 3S3H
2 1.66
17.65 T
3S3P 2
0.04 0.40
ns T
3H3P 4
0.04 0.71
ns S
3H3P 4
0.04 0.47
ns T
3S3H3P 4
0.06 0.59
ns Residual
72 0.09
a
ns, P . 0.05; P , 0.05; P , 0.01; P , 0.001.
C .J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26
21
Fig. 2. Mean total annual numbers of settlers area of patch n 5 3 of different size 6, 3 and 1.5 cm at Sites
3 and 4 on Low, Mid and Upper heights of Chamaesipho’s distribution in December, 1991 and 1992. Note different scale on y-axis among sites and heights.
increased availability of free space does not control numbers of settling Chamaesipho cyprids and that larval choice is operating.
3.3. Influence of conspecific adults at perimeters on gregarious settlement When total numbers of settlers were divided by the perimeter of 6, 3 and 1.5 cm
patches to account for the influence on settlement of different relative exposure to adults along perimeters, most settlement occurred in 1991 at Site 3 on Low heights. Even
though data were standardised, most settlers were recorded in the smallest patches, but
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.J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26
similar numbers of barnacles settled in the larger patches 1.5 cm .3 cm56 cm; Fig. 3;
Table 1c. These results suggest that, while bordering adults provide cues for settlement, other processes are also operating.
Fig. 3. Mean total annual numbers of settlers perimeter of patch n 5 3 of different size 6, 3 and 1.5 cm at
Sites 3 and 4 on Low, Mid and Upper heights of Chamaesipho’s distribution in December, 1991 and 1992. Note different scale on y-axis among sites and heights.
C .J. Jeffery J. Exp. Mar. Biol. Ecol. 252 2000 15 –26
23
4. Discussion
