Vorschau

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Abstract

Marine biofouling is a global problem with a negative impact on several industrial and maritime branches, causing immense costs. Alongside with the economic consequences of colonization of surfaces, the environmental aspects should not be underestimated. Because of the predominant use of heavy-metal based antifouling coatings in the last decades, the most prominent component of which is tributyltin, TBT, several unacceptable environmental `side effects' on non-targeted species have emerged. This led to a global ban of the use of TBT-containing coatings in 2008. Since then, the research efforts focus on the development of surfaces which solely rely on physicochemical properties to mitigate the undesired accumulation of biomass. For identification of surface properties which influence and guide settlement, a better understanding of the colonization mechanisms of the target organisms is required. The purpose of this work was the investigation of the exploratory behaviour of barnacle larvae (cyprids) of Balanus amphitrite. This species was selected because it is widely spread in several geographic regions and contributes significantly to biofouling pressure. To enable the extraction of three-dimensional swimming trajectories, a stereoscopic setup was developed. It was utilized to quantify the pre-settlement behaviour of cyprids on surfaces with different wettability, hydration or charge. The analysis of the data allowed the identification of basic reoccurring patterns in the motion of cyprids, i.e. spiraling, swimming, sinking, rotating and walking. A detailed evaluation of the distribution of these patterns revealed that swimming was most frequently observed, followed by sinking which seemed to be its counterpart. Furthermore, it could be shown that most surface contacts emerged after sinking, while an active swimming towards the substrate was seldom observed. In addition, the general distribution of cyprids in the water column demonstrated that there was a clear preference for interfacial regions, and that the main occurrence of cyprids concentrated in three distinct zones above surfaces - the lower, bulk and upper swimming region, denoting the distance of the larvae from the substrate. It was revealed that the settlement preferences of cyprids were reflected in the motility parameters of exploration, i.e. linearity of the locomotion, mean velocity, swimming depth and extent of explored area. Once on a surface, cyprids initiate a close surface inspection, involving bipedal walking. The quantification of this mode of movement showed that the step duration and step velocity correlated with the attractiveness of the surface for settlement. Moreover, an analysis of the complete exploration process - from swimming via close surface inspection to interface interactions, confirmed literature reports that the number of surface touchdowns and the amount of organic deposit left behind were guided by the attractiveness of the substrate for biofouling. In addition to this organic deposit, macromolecules and other compounds accumulate on surfaces, immediately after these have been placed in an aquatic environment. The influence of this `conditioning' film on the exploratory behaviour was investigated and it was proven to cover the initial chemical end groups of different substrates. This masking process provoked cyprids to explore non-attractive conditioned surfaces in the same manner as attractive ones. Except on model surfaces, the exploratory behaviour was also investigated on commercially available hydrogel-based coatings and it was found that the motility of cyprids started to decrease gradually immediately after surface contact and after 4h it completely stopped, which was contributed to mortality of the organisms caused by the paints. Finally, the stereoscopic setup was modified to allow measurements in situ, underwater. The results of the field experiments at two test sites are discussed with respect to the applicability of the system for measurements in the natural environment and its capability to reveal colonization dynamics of marine organisms.