Variations in the abundance and structural diversity of microbes forming biofilms in a thermally stressed coral reef system

•Microbial biofilms with potential ability to support larval settlement and metamorphism in thermally stressed coral reef systems.•Vibrio with ability to precipitate CaCO3 dominated the biofilms•Potential morphogen producers like Pseudoalteromonas, diatoms and rhodophyta detected throughout the biofilm succession.•Stable bacterial biofilm community developed despite the natural elevation in water temperature.

Little information is known about biofilm formation in the thermally stressed coral reef systems north of the Arabian Gulf. The current study investigates the abundance and diversity of marine microbes involved in biofilm formation and their succession over a period of 14 weeks (May-August 2007) at temperatures exceeding 32 °C. The results showed variations in microbial numbers and the development of more stable biofilm communities as the biofilms aged. The culture-dependent technique and microscopic examination of the developed biofilms showed the dominance of key species known for their role in precipitating CaCO3 such as Vibrio and in facilitating coral larvae settlement and metamorphosis such as Pseudoalteromonas, Bacillariophyceae and Rhodophyceae. The results revealed biofilm formations with microbial diversities that have the potential to support the larval settlement and metamorphism of marine organisms and to consolidate and stabilize biofilms via the process of calcification in the thermally stressed coral reef system considered herein.