Dust-borne microbes affect Ulva ohnoi's growth and physiological state

The marine macroalgae Ulva sp. is considered an ecosystem engineer in rocky shores of temperate waters worldwide. Ulva sp. harbors a rich diversity of associated microbial epibionts, which are known to affect the algae's typical morphological development and 'health'. We examined the interaction between airborne microbes derived from atmospheric aerosols and Ulva ohnoi growth and physiological state. Specifically, we measured U. ohnoi growth rates and photosynthetic efficiency (Fv/Fm), alongside its microbial epibionts abundance, activity and diversity following dust (containing nutrients and airborne microorganisms) or UV-treated dust (only nutrients) amendments to filtered seawater. Parallel incubations with epibionts-free U. ohnoi (treated with antibiotics that removed the algae epibionts) were also tested to specifically examine if dust-borne microbes can replenish the epibiont community of U. ohnoi. We show that viable airborne microbes can restore U. ohnoi natural microbial epibionts communities, thereby keeping the seaweed alive and 'healthy'. These results suggest that microbes delivered through atmospheric aerosols can affect epiphyte biodiversity in marine flora, especially in areas subjected to high annual atmospheric dust deposition such as the Mediterranean Sea.