Introduction. Marine organisms produce a variety  of secondary metabolites mainly for achieving the defence against the competitors and predators. These compounds could be used as natural product antifoulants for the management of biofouling growth on marine structures. Objectives. To understand the antifouling defence strategies of marine macroalgae collected from the Red Sea. Methodology. The macroalga Dictyota dichotoma was collected from the Obhur Creek of Red Sea, Saudi Arabia and extracted using methanol. Surface and total extraction methods were performed and tested against a bacterial strain isolated from the microfouling assemblage. Results. The extracts obtained from the macroalgal samples have strong antibacterial and antibiofilm activities against the bacterial strain isolated from the marine microfouling assemblage. The total extracts showed strong bacterial growth inhibitory activities in culture plate method. In microtitre plate assay, surface extract showed strong biofilm inhibitory activity. GC-MS analysis indicated considerable variations in the metabolic profile of the surface and total extracts. Conclusion. This study revealed the importance of surface-associated compounds in antifouling defence mechanism of the marine macroalgae.

Introduction. Marine organisms produce a variety  of secondary metabolites mainly for achieving the defence against the competitors and predators. These compounds could be used as natural product antifoulants for the management of biofouling growth on marine structures. Objectives. To understand the antifouling defence strategies of marine macroalgae collected from the Red Sea. Methodology. The macroalga Dictyota dichotoma was collected from the Obhur Creek of Red Sea, Saudi Arabia and extracted using methanol. Surface and total extraction methods were performed and tested against a bacterial strain isolated from the microfouling assemblage. Results. The extracts obtained from the macroalgal samples have strong antibacterial and antibiofilm activities against the bacterial strain isolated from the marine microfouling assemblage. The total extracts showed strong bacterial growth inhibitory activities in culture plate method. In microtitre plate assay, surface extract showed strong biofilm inhibitory activity. GC-MS analysis indicated considerable variations in the metabolic profile of the surface and total extracts. Conclusion. This study revealed the importance of surface-associated compounds in antifouling defence mechanism of the marine macroalgae.