Water chlorination and environmental factors are associated with dolphin skin microbiome diversity and composition

Dolphin skin microbiome is constantly exposed to a microorganism-rich medium and represents the first line of defense from environmental stressors and potential pathogens. While some bacteria cause skin diseases and ulcerating wounds, high water temperature, salinity, and pH seem to lower dolphin wound rates and promote accelerated scar healing. Despite its importance in host health, interactions of dolphin skin microbiome with physical and chemical characteristics of habitats remain poorly understood. Using 16S rRNA metabarcoding, we characterized and compared the skin bacteria communities of 87 common bottlenose dolphins ( Tursiops truncatus ) and 4 rough-toothed dolphins ( Steno bredanensis ) living in chlorinated tanks, enclosed lagoons, or open bays. Dolphins living in enclosed lagoons and open bays had skin microbiomes dominated by Enhydrobacter , a bacteria genus found on cetacean skin that occurred at low relative abundance in dolphins in chlorinated tanks. The skin microbiome of dolphins in chlorinated tanks was the most diverse and showed a significant increase of Staphylococcus relative abundance and prevalence when compared to enclosed lagoons and open bay specimens. Among dolphins sampled in open bays across seasons, summer conditions (higher temperature and pH) were associated with up to 10-fold lower Mycobacterium relative abundance, as well as a significant decrease of Streptococcus prevalence, genera associated with slow healing of cutaneous wounds in dolphins. Our results reveal novel insights into the association of physical/chemical environmental factors with dolphin skin microbiome composition. We highlight how the relative abundance and prevalence of potentially opportunistic bacteria on dolphins may vary across human-managed and wild habitats, providing crucial information for the improvement of dolphin husbandry practices and conservation.