K .M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83
69
depth of submersion ‘depth’ and monthly interval of submersion ‘month’. Topog- raphy, depth and month were considered as fixed factors and station was considered as a
random factor. In the analyses of choice experiment on subdivided Plexiglas Section 2.2.2. the orthogonal factors were ‘topography’ and ‘month’ and they were considered
as fixed. Differences in settlement and behaviour Sections 2.3.1 and 2.3.2 between surface treatments were analysed by one-factor ANOVA. A posteriori comparisons were
performed using Student–Newman–Keuls procedure and tests for homogeneity of variances were performed using Cochran’s test Winer et al., 1991. All data sets, except
the proportion of settlers on smooth versus micro-textured sections Section 2.2.2 and the behavioural time budgets Section 2.3.2, showed heteroscedasticity and were
therefore log-transformed log prior to the analysis of variance ANOVA. This also
10
implies that interactions among factors should be interpreted on a proportional scale. In both field experiments Section 2.2 the data were log-transformed as logrecruitment1
0.0001 and the micro-textured treatments were tested against the smooth controls. In the laboratory study Section 2.3.1 the data were log-transformed as logsettlement10.1
and settlement on textured treatments were tested against settlement on untreated petri dish controls. Laboratory data on behavioural time-budgets Section 2.3.2 were tested
using a one-factor ANOVA, and a priori means comparison contrasts for tests of surface texture against the smooth control.
3. Results
3.1. Characterisation of micro-textured surfaces 3.1.1. Analysis of surface topography
Table 1 shows the roughness parameters R , R and R
for the tested surface
a z
sm
textures. The roughness parameters on smooth PMMA panels used as controls were clearly different as compared to sanded panels Table 1, Figs. 1a and 1b. The average
roughness of the profile R was 28 times larger, the maximum height of the profile R
a z
27 times larger and the mean width of the profile elements R 18 times larger on
sm
sanded panels as compared to smooth panels. There were large differences in the roughness parameters between the moulded panels with substantial increase in R and R
a z
parameters from smooth ,20,170,190¯355 mm Table 1. The R parameter
sm
showed a similar increase except that the width of the profile elements did not differ between smooth and 20 mm panels Table 1, Fig. 1a and Fig. 2a–d. The roughness
parameters for the PVDF riblet film Fig. 1c given by the manufacturer 3M Inc. is shown in Table 1.
3.1.2. Analysis of surface chemistry ESCA revealed carbon and oxygen in ratios of 3:1 that reflects the molar composition
of PMMA. In addition to carbon and oxygen small amounts of silicon 0.5 were detected. The sanding procedure and moulding procedure did not appear to affect the
relative composition of C and O, but reduced the Si content from 0.5 to below detection. Untreated panels, therefore contained low levels of Si that were removed from
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.M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83
the panels during the sanding and moulding procedure. The levels of Si were not apparently affected by the heating procedure in the oven.
3.2. Field studies of Balanus improvisus recruitment on micro-textured surfaces 3.2.1. Recruitment on smooth and micro-textured surfaces
Over all depths, months and stations the mean recruitment of B . improvisus was
reduced by 82611 n 55 on micro-textured surfaces as compared to smooth controls in the field experiments. Fig. 5a shows the reduction in recruitment as a function of
topography and depth in July and Fig. 5b shows the reduction in recruitment as a function of topography and month averaged for all stations. These two graphs suggest
that topography had a consistent effect on recruitment irrespective of depth and month although the temporal and depth variation increased when settlement was low, e.g. for
the depth interval 4–5 m Fig. 4a and for June Fig. 4b. Recruitment on sanded panels
Fig. 5. Percentage reduction mean695 CI in recruitment on sanded compared to smooth PMMA panels. a Reduction as a function of depth in July 1998 n 516, b reduction as a function of month at 0–3 m depth
and averaged over all locations n 58.
K .M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83
71
Fig. 6. Recruitment mean695 CI, n 56 of B . improvisus on smooth S and sanded T PMMA panels for
different locations and months averaged over the depth interval 0–3 m. Y-axis on a logarithmic scale.
as a function of topography, month and station, averaged for the top three depth intervals 0–3 m was consistently low during the whole settlement period Fig. 6. During peak
22
settlement in July mean recruitment52.660.7 ind. cm on smooth panels and
22
50.160.03 ind. cm on sanded panels, Fig. 6 recruitment was reduced by 9268 on
sanded panels as compared to controls Fig. 5b. In June when the mean recruitment was
22 22
as low as 0.0560.02 ind. cm on smooth and 0.00460.002 ind. cm
Fig. 6 on sanded panels, recruitment on sanded surfaces was still reduced by 68636 although
the variation among stations and depths was more pronounced compared to subsequent months Fig. 5b. The major source of the variation in recruitment on smooth surfaces is
due to differences in recruitment among stations Fig. 6. For instance the recruitment on smooth surfaces including the top three depth intervals 0–3 m and all five months was
22 22
2.260.5 ind. cm in station L5 and 0.0860.05 ind. cm
in station L3 Fig. 6. Despite this spatial variation the difference in recruitment between smooth and micro-textured
surfaces was very consistent Fig. 6. ANOVA detected significant interactions with the random factor station Table 2.
Although the effect sizes of these interactions e.g. the interaction among all factors were generally small the statistical power to detect these differences is very strong.
Inspection of the interaction between topography and station shows that the qualitative difference between smooth and rough surface is consistent although the magnitude
varies between stations Fig. 6. Considering the consistent qualitative pattern in the interactions with the factor station we interpret the main effect of topography as highly
significant. There were no significant interactions among the fixed factors topography, depth and time interval indicating a general effect of topography in space and time.
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.M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83 Table 2
Four-factor ANOVA testing the effects log -transformed of micro-texture, time of exposure, depth and
10 a
location on the recruitment of Balanus improvisus in a field experiment Source
df Mean square
F-value P-value
Error term Topography T
1 129
64.2 0.0001
T3S Depth D
2 7.34
7.87 0.0051
D3S Month M
4 85.0
34.0 0.0001
M3S Station S
7 22.2
68.1 0.0001
Residual T3D
2 1.59
1.64 0.23
T3D3S T3M
4 1.55
2.00 0.12
T3M3S T3S
7 2.02
6.19 0.0001
Residual D3M
8 1.11
1.38 0.23
D3M3S D3S
14 0.93
2.86 0.0005
Residual M3S
28 2.50
7.67 0.0001
Residual T3D3M
8 0.30
0.57 0.80
T3D3M3S T3D3S
14 0.97
2.99 0.0003
Residual D3M3S
56 0.81
2.47 0.0001
Residual T3M3S
28 0.77
2.37 0.0003
Residual T3M3D3S
56 0.53
1.62 0.0073
Residual Residual
240 0.33
a
The treatment ‘Topography’ included sanded and smooth panels. The treatment ‘Depth’ included the three intervals 0–1, 1–2, and 2–3 m. The treatment ‘Month’ consisted of five subsequent months with panels
exposed for 1 month. The location factor ‘Station’ included eight randomly selected locations.
3.2.2. Choice experiment on subdivided PMMA panels Compared to smooth controls all micro-textured surfaces reduced recruitment to a
similar degree Fig. 7. Peak settlement occurred in August and the mean recruitment on
22
smooth controls was 1.460.7 ind. cm while subdivided 190 mm panels had the lowest
22
recruitment with 0.260.1 ind. cm Fig. 7. The effect of topography was general,
irrespective of monthly interval Table 3, although no statistical difference in recruitment between panels with different sizes of micro-texture was detected SNK,
P .0.05. A choice situation was included within each panel where cyprids could choose to
settle on a micro-textured part or a smooth part of the panel. The distribution of barnacles between these parts of the panel were not as obvious as expected from the
among panel analysis. There was no significant difference in the proportion of barnacles that settled on the smooth part of the panel as compared to the micro-textured part
two-factor ANOVA, F
51.0, P.0.05, although more barnacles settled on the
3,112
smooth part in July and August compared to September and October Fig. 8, two-factor ANOVA, F
54.3, P,0.05, SNK, P,0.05. This fraction varied considerably both
3,112
within and among treatments and between monthly interval Fig. 8. 3.2.3. Summary of recruitment as a function of different scales of surface texture
Plots of recruitment of B . improvisus on the field-exposed panels measured against
roughness parameters indicate that there is a narrow range of surface roughness that strongly affects recruitment Fig. 9. Recruitment was almost absent when the surface
topography had a roughness height R within 30–45 mm Fig. 9a, an average
z
K .M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83
73
Fig. 7. Recruitment mean695 CI, n 58 of B . improvisus on panels with different scales of micro-texture
compared to a smooth control in August 1998. The sizes in the graph refer to the mesh-size used to mould each textured surface. For measured topographic dimensions see Table 1.
roughness R within 5–10 mm Fig. 9b and a roughness width R within 150–200
a sm
mm Fig. 9c. 3.3. Cyprid settlement and behaviour on micro-textured surfaces
3.3.1. Cyprid settlement in choice experiment Micro-textured surfaces, as in the field experiment, significantly reduced settlement as
compared to smooth controls Fig. 10, one-factor ANOVA, F 541.0, P,0.05,
6,21
although no differences between different scales of roughness were detected SNK, P .0.05. Treatments with the riblet-film and mouldings from 170 and 355 mm plankton
nets, however, completely inhibited settlement Fig. 10. The distribution of settled cyprids on the subdivided surfaces in the laboratory study was less variable than in the
field experiment. The only treatments where any cyprids settled on the micro-textured
Table 3 Two-factor ANOVA testing the effects log -transformed of micro-texture and time of exposure on the
10 a
recruitment of Balanus improvisus in a field experiment Source
df Sum of squares
Mean square F-value
P-value Topography T
4 6.42
1.60 9.65
0.0001 Month M
3 19.3
6.45 38.8
0.0001 T3M
12 2.14
0.18 1.07
0.39 Residual
140 23.3
0.17
a
The treatment ‘Topography’ included four moulded micro-textures and one smooth panel, and ‘Month’ consisted of four subsequent months with panels exposed for 1 month.
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Fig. 8. The fraction mean695 CI, n 58 of B . improvisus recruits on the smooth compared to the
micro-textured part of moulded PMMA panels. The legend refers to the four micro-textures tested. Fractions below 0.5 indicate that the majority of barnacles were found on the smooth section.
portion of the surfaces were on 20, 190 mm and sanded panels although the fraction that settled onto the smooth portion was still high 70, 80 and 80, respectively. Cyprids
appeared more selective about their settlement site in the laboratory as compared to the field and the proportion settled on the smooth part of the panels was significantly higher
in the laboratory experiments two-factor ANOVA, F
554.0, P,0.05.
1,24
3.3.2. Analysis of settlement behaviour as a function of micro-texture Video-recording and analysis of cyprid exploratory behaviour on different topographic
surfaces revealed a strong effect of micro-texture on cyprid behaviour. When comparing the two main categories of cyprid behaviour surface exploration and swimming, there
was an obvious pattern where cyprids spent more time exploring on smooth surfaces than on micro-textured surfaces Fig. 11. The proportion of time that cyprids spent
exploring the surface differed between the smooth control and all micro-textured surfaces except for the moulded 190-mm treatment one-factor ANOVA, F
55.1,
6, 98
P ,0.05. There was, however, no significant difference in the proportion of time exploring between different scales of micro-texture Fig. 11, SNK, P .0.05.
Three phases of exploratory behaviour were identified, broad exploration, close exploration and inspection. The proportion of time cyprids spent in the different
exploratory phases differed among surface treatments and showed a complex pattern Fig. 12. The analysis of variance showed significant effects of micro-texture for
inspection behaviour One-factor ANOVA, F 54.0, P,0.05. Cyprids spent sig-
6, 98
K .M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83
75
Fig. 9. Summary of the recruitment mean695 CI, n 516 of B . improvisus on surfaces with different
micro-textures. Recruitment in July and August is plotted against three different roughness parameters measured on the micro-textured surfaces: a R maximum height of the profile, b, R average roughness,
z a
and c R mean width of profile elements.
sm
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.M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83
Fig. 10. Settlement mean695 CI, n 55 of B . improvisus cyprids as a function of different micro-textures,
including a smooth control, in a laboratory experiment. For topographic dimensions see Table 1.
nificantly less time inspecting the textured surfaces compared to the smooth control means comparison contrast F
54.3, P,0.05. It is interesting to note, however, that
1,98
the distribution of cyprid exploratory phases on the moulded 20-mm surface resembled
Fig. 11. Time budgets mean695 CI, n 515 of cyprid exploration on surfaces with different micro-textures, including a smooth control. B
. improvisus cyprids were recorded for 5 min and their behaviour was divided into surface exploration or swimming. For topographic dimensions see Table 1.
K .M. Berntsson et al. J. Exp. Mar. Biol. Ecol. 251 2000 59 –83
77
Fig. 12. Time budgets mean695 CI, n 515 of cyprid behaviour on surfaces with different micro-textures, including a smooth control. B
. improvisus cyprids were recorded for 5 min and their behaviour was divided into three different exploration phases. For topographic dimensions see Table 1.
the distribution on smooth surfaces Fig. 12. The time budgets of the exploratory phases changed and some phases even disappeared on surfaces with larger structures as
compared to the smooth surface, e.g. close exploration was absent on the moulded 170-mm surface and broad exploration was absent on the moulded 355-mm surface Fig.
12. Broad exploration was most frequent on the moulded 190-mm surface and the riblet surface Fig. 12. Close exploration was more frequent on the smooth surface as
compared to moulded 170-mm, moulded 355-mm and sanded surfaces Fig. 12. Cyprids allocated more time to inspection behaviour on moulded 355-mm than on moulded
170-mm, moulded 190-mm surfaces and the riblet surface, and inspection was more common on the smooth surface than the riblet surface.
There appeared to be three groups with similar time budgets Figs. 11 and 12. The smooth surface forms a group together with the moulded 20-mm surface, and the
190-mm surface forms a group together with the riblet surface. Finally, the time budgets of cyprids on the moulded 170-mm surface and the sanded surface are similar. Cyprid
behaviour on the moulded 355-mm surface did not have much in common with any other treatment. The time budget of behaviours on the moulded 190-mm surface and the riblet
treatment are reversed as compared to the smooth and the moulded 20-mm surfaces Fig. 12. This seems to be a consequence of the relatively higher proportion of broad
exploration on the riblet film and the moulded 190-mm surface. Although the micro- texture of these surfaces had rather different shapes they appeared to encourage broad
exploration to a similar degree. On the riblet film cyprids tended to follow the direction of the grooves for 1–2 cm and then to swim off to make new trials on different sites.
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Exploration behaviour appeared to be somewhat different on sanded and moulded 170-mm, and 355-mm surfaces compared to other micro-textured treatments. Cyprids
tended to progress from swimming behaviour to inspection with the preceding exploratory phases shortened or absent. On moulded 170-mm surfaces cyprids went
straight from broad exploration to inspection without performing close exploration. Finally, it is worth emphasizing that although the sampling of behaviours started when
the cyprids made the first contact with the substrate, most micro-textured surfaces were rejected before the end of each recording sequence which demonstrates the cyprids’
aversion against textured surfaces, at least within the scales covered by this study.
4. Discussion
