inter-specific variation in adhesion strength of barnacles on

Inter-specific variation in adhesion strength of barnacles on foul-release

coatings

Teo, Serena Lay-Ming, Lim Chin-Sing & Sin Tsai-MinTropical Marine Science InstituteNational University of Singapore

Singapore

Two major types of Commercial Antifouling Coatings:

1) Conventional Biocide based ablative coatings

2) Fouling release silicon elastomeric coatings

EXPERIMENT: Barnacle Adhesion on Intersleek 425• Panels were immersed at Singapore Test Site (Nov 05- ) • 3 x Intersleek 425 panels x Front, Back• panels were gently wiped clean then allowed to foul with barnacles• Readings taken approx 3 weeks – 1 month later.• 20-30 force gauge readings were taken for each facing of the panels

L-R: Amphibalanus (=Balanus)• cirratus• reticulatus• amphitrite

ASTM D 5618-94 :Standard test method for measurement of barnacle adhesion strength in shear

• Test surfaces were immersed according to ASTM D3623• Only small barnacles 5- 20mm base diameter, at least 20mm away from edge, not overgrown or in contact with other barnacles were selected.• The force gauge was placed at base of barnacle, and shear force applied parallel to surface, at approx 4.5 N/s until the barnacle is detached. • The force was recorded. If base is broken, test is invalid. At least 20-30 barnacles were tested for each panel facing.• The barnacles were collected and returned to lab for identification. The area of the base was calculated using a digitiser pad.

Swain et al. (2000) : California, Florida & Hawaii < < Italy, Singapore. For Intersleek: Hawaii = 0.046MPa± 0.015 cf Singapore 0.125MPa±0.059

Barnacle Plaque

Plaque formation described by Wiegemann & Watermann (2003) –abnormal concave shape base plates filled with a highly hydrated adhesive plaque.

Likely to be part of a repair mechanism to bridge gap between the base and substratum; at the expense of cross-linking and lower cohesive strength

This loose hydrated formation results in greaterThis loose hydrated formation results in greater elasticity which is favourable for adhesion to flexible elastic coatings.

Holm et al. 2005 – demonstrated difference in adhesive properties of different genetic lines of barnacles

Wendt et al. 2006 – demonstrated lower critical removal stress associated with individuals with atypical cupped base

Plaque Cover and Thickness

Aspect Ratio = Height / Diameter

Questions:

1. Does adhesion strength change over time?

2. Is there a difference in adhesion strength between species of barnacles?

3. Is the difference in adhesion strength related to differences in growth form (size, aspect ratio) or plaque (cover, thickness)?

1. Does adhesion strength change over time?• Two way ANOVA with date, species vs calculated force: date F5,10=8.7,

p<0.0001; date x species F10,365=2.20, p<0.05)

• A. amphitrite – no significant difference in adhesion strength between sampling dates (but sample size/individuals small?)

• A. reticulatus, A. cirratus – Post hoc analysis showed significant differences among months

Adhesion Strength (MPa)

0.12

cirratus

0

0.02

0.04

0.06

0.08

0.1

Mar-06 Apr-06 Jun-06 Jul-06 Sep-06 Jun-07

Cal

c fo

rce

(MPa

)

reticulatus

Adhesion Strength (MPa)

0

0.02

0.04

0.06

0.08

0.1

0.12

Feb-06 Mar-06 May-06 Jul-06 Aug-06 Oct-06 Nov-06 Jan-07 Mar-07 Apr-07 Jun-07 Aug-07

Cal

c fo

rce

(MPa

)

cirratus reticulatusAdhesion strength

0

10

20

30

40

50

60

70

80

Time

% fo

ulin

g of

bar

nacl

es

Barnacle monthly recruitment

2. Is there a difference in adhesion strength between the two species of barnacles?

A. cirratus A. reticulatus 0.062 ± 0.032 (all data) 0.063 ± 0.029 (all data) 0.092 ± 0.04 (Jul 06) 0.086 ± 0.031 (Jul 06, Jun 07) 0.071 ± 0.026 (Mar, Sep 06, Jun 07) 0.055 ± 0.024 (rest of months)( p ) ( )0.037 ± 0.02 (Apr, Jun 06) • No difference if you average the whole data set• But significant difference in adhesion strength for the two species was recorded in some months (eg. April, June 06).

3a. Is the difference in adhesion strength related to differences in growth form (size, aspect ratio)?

•Two way MANOVA detected significant effects on species and date with aspect ratio F2,10=3.745, F5,10=2.481, p<0.005)•Post-hoc Fisher LSDs detected significant differences in aspect ratio

Aspect Ratio (height:diameter)

0 6

0.3

0.35

0.4

0.45

0.5

0.55

0.6

Mar-06 Apr-06 Jun-06 Jul-06 Sep-06 Jun-07

3a. Is the difference in adhesion strength related to differences in plaque (cover, thickness)?

•Forward stepwise multiple regression was performed for each barnacle species with calc force as dependent variable and av height, aspect ratio, plaque thickness and cover as independent predictors

•Barnacle height is important (cf. aspect ratio – tall barnacles, lower adhesion strength)•Plaque cover consistently retained in regression equation for all 3 species

Species df1, df2 Regression F

Regression p

R2 term beta Term p

amphitrite 1,35 2.97 ns 7.8 Pl cover

-0.28 ns

<0.05 cirratus 3,109 8.10 <0.001 16.0 Av ht -0.371 <0.0001 Pl

cover -0.432 <0.01

Pl thick 0.26 0.09 reticulatus 3,221 12.56 <0.0001 13.4 Av ht -0.213 <0.01 Pl

cover -0.232 <0.001

aspect -0.16 <0.05

3

• For most part, A. reticulatus had higher plaque cover and thickness than A. cirratus, except during peak settlement period in both July 06 and Jun 07.

• For A. reticulatus, taller barnacles had more plaque cover and thickness

0

1

2

Mar-06 Apr-06 Jun-06 Jul-06 Sep-06 Jun-07

Av

Plaq

ue C

over

SUMMARY OF RESULTS:

1. Adhesion strength fluctuated over time. This may be a result of fitness or environmental parameters.

2. The effect may also be related to the morphology of barnacles in the sample.

3. Tall barnacles have lower adhesion strength, which may/may not be associated to the presence of plaque.

4 A reticulatus appears to have a greater propensity to produce plaque than A4. A. reticulatus appears to have a greater propensity to produce plaque than A. cirratus (resulting in the presence of more smaller, tall individuals in the samples than A. cirratus??).

5. Increased plaque cover reduces adhesion strength.

6. When aspect ratio was similar between the 2 species, adhesion strength was not significantly different even when the plaque cover was significantly different, suggesting that for this test, barnacle shape had a greater effect on adhesion strength measurements than effects arising from plaque alone.

ACKNOWLEDGEMENTS

• Financial support from the US Office for Naval Research through grant N00014-04-1-0789, and Collaborators from the ONR Coatings Program for their assistance and good advice.

• Mr Mohammad Razali bin Duriat for field technical support,• Colleagues from the marine laboratory at Tropical Marine Science Institute for their assistance during the project.

• The Republic of Singapore Yacht Club for generously hosting our field test site and researchand research.