Abstract
Under natural conditions, barnacles, one of the most prominent marine hardfouling organisms, encounter a vast variety of heterogeneous surfaces including artificial ones, such as ship hulls on which they adhere efficiently. Despite intensive research in the last decades, it is still not clear, how material related factors influence the fouling development under natural conditions, and whether roughness at a microscale affects the release dynamics of barnacles. In order to shed light on the relationship between these substrate factors and their effect on biofouling, both settlement and fouling development of Balanus (=Amphibalanus) improvisus was evaluated on epoxy resin and polyvinylsiloxane (PVS) substrates differing in their roughness (flat, asperity sizes: 0.3µm, 1µm, 3µm, 9µm, 12µm) in a static field trial in the Baltic Sea for 17 weeks performed in 2014. All barnacles on these tested surfaces were individually tracked on a weekly basis, in order to calculate the release to settlement ratios (r/s), to evaluate the fouling- release performance and to monitor the actual attachment duration. It was demonstrated that both stiffness and surface free energy had no strong effect on initial settlement. The total fouling accumulation was nearly identical for epoxy resin and PVS, if fallen-off barnacles were included in the analysis. Roughness influenced initial settlement and fouling development. On PVS the r/s nged between 0.5-0.7 and the attachment duration was around four weeks. However, samples with a roughness of 9µm displayed a lower r/s ratio (0.35) and barnacles showed longer attachment durations (8 weeks). In a second field trial performed in 2017, attachment forces of barnacles were measured after the samples had been immersed for 10 weeks in the Baltic Sea. The shear stresses obtained were similar for substrates with different roughness with around 0.12 MPa and were independent of the barnacle’s size. These findings show that roughness even at the micro scale can impact the fouling release ability of a surface.
Highlights
Among the marine hardfouling organisms, barnacles (Cirripedia, Thoracica) represent one of the most successful groups
From week 9 on, actual barnacle densities remained stable for all roughness samples up to week 13 followed by a second accumulation phase until the end of the experiment
No strong influence of stiffness and surface energy on initial settlement of B. improvisus was observed under natural conditions carried out in the Baltic Sea, Kiel, Germany
Summary
Among the marine hardfouling organisms, barnacles (Cirripedia, Thoracica) represent one of the most successful groups. The chemical background of underwater attachment in barnacles is complex and involves a range of substance classes, such as lipids, antimicrobial peptides and binding proteins (Dickinson et al, 2009; Burden et al, 2012; Kamino, 2013; Gohad et al, 2014; Kamino, 2016; So et al, 2016; Fears et al, 2018) Most of these biological compounds are multifunctional and interactions between them and the underwater substrates are still largely unknown. Some barnacles including Balanus [=Amphibalanus] improvisus (Pitombo, 2004) produce a calcareous base plate in the adult phase and secrete their cement underneath it in a stepwise process during growth (Burden et al, 2014). As they grow, periodic molts take place every few days. This means that barnacles have to continuously produce adhesive onto the corresponding surface which makes adhesion a permanent challenge in their life
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