Understanding of Marine Underwater-Adhesive and Fouling Interface

Abstract

Robust adhesion to targeted surfaces is crucial for the survival of the marine fouling organism because continuous mechanical stresses from wind, waves, or buoyancy exist in the marine environment. For this reason, uncountable marine fouling organisms secure their bodies to a surface using various fouling mechanisms (e.g., holdfasts(Waite 1992), cement(Kamino et al. 2000), suction(Hiew and Miserez 2017), and mucus(Hennebert, Wattiez, and Flammang 2011)). Although marine fouling causes a great loss in the shipping and marine industry, it also provides a clue to the development of a new type of bioadhesive due to the marine organisms maintaining strong adhesion even in a humid environment. Therefore, an integrated understanding of the fouling/antifouling phenomenon across various marine species is essential for minimizing the economic and industrial losses caused by the fouling/anti-fouling phenomenon and for developing a new bioadhesive.

This dissertation focuses on the biological understanding that occurs at the interface where the macrofouling of marine organisms occurs and suggests new utilizing insights beyond the understanding of biological phenomena. Specifically, in chapter 2, using Korean fan shell Atrina pectinata, which has the characteristic morphology that the interface between stiff byssal threads and soft tissues is distributed all over an extended organ, a novel strategy for mitigating contact damage at a mechanically mismatched interface was suggested. A wide distribution of various types of carbohydrates and lectins at the mechanically mismatched interface of the byssus of Atrina was found using histological methods and proteomics. Based on these results, reversible and robust interactions between the carbohydrate and lectins at the interface would play a major role in mitigating the contact damage at the Atrina interface and it would be useful to use a wide range of energy dissipation in the load bearing interfaces.

In chapter 3, the change of the adhesion mechanism according to stiffness of the adhesive interface of the mussel was investigated. I identified a concept in the development of antifouling surfaces based on understanding the surface stiffness recognition procedure of mussel adhesion at the genetic level. It was found on a soft surface that the combination of decreased adhesive plaque size, adhesion force, and plaque protein downregulation synergistically weakens mussel wet adhesion and sometimes prevents mussels from anchoring, mainly due to transcriptional changes within the mechanosensing pathway and the adhesive proteins in secretory glands. In addition, the use of soft substrates or antagonists of surface mechanosensing behavior suppresses mussel fouling significantly.

In Chapter 4, ‘urchin barrens’, the marine conditions with overgrowth of coralline algae and sea urchins with destruction of kelps and causes severe economic loss and loss of biodiversity, was investigated from the perspective of anti-fouling effect of coralline algae. The study was conducted assuming that the antifouling material of coralline algae which dominates urchin barrens region increases the antifouling ability in the changing marine environment and kills the surrounding seaweed. As a result, a significant amount of calcium sulfide (CaS) was found on the surface of L. yessoense, a representative coralline alga most frequently found in urchin barrens areas of South Korea. Calcium sulfide (CaS) can produce hydrogen sulfide (H2S) when in contact with water and hydrogen sulfide is usually toxic to living organisms. The toxicity of hydrogen sulfide is very sensitive to the surrounding pH. At a normal ocean pH (~8), more than 90% of the hydrogen sulfide group exists in the form of charged disulfide (HS-), so it neither passes through the cell membrane nor cause toxicity. However, as the environment becomes more acidic by ocean acidification, the amount of molar fraction present in the form of toxic hydrogen sulfide (H2S) among the hydrogen sulfide groups (H2S, HS-, S2-) increases exponentially. In addition, the total amount of hydrogen sulfide group generated from calcium sulfide (CaS) also tended to increase in an acidic environment. Therefore, it has been revealed that the acidified marine environment can lead urchin barrens by increasing the amount of toxic gas generated from the coralline algae.