Microbiome plasticity during the early life-stage of the angelshark (Squatina squatina) in Las Teresitas (Canary Islands)

Shark microbiome studies offer acute insights into host health, immunity, and ecological interactions, yet remain poorly studied compared to other marine vertebrates. Shark-associated microbial communities, despite being species-specific, are influenced by environmental conditions and feeding ecology. In this study, we aimed to characterize shifts in the microbiome of the Critically Endangered angelshark ( Squatina squatina ) during the early stages of development and to assess how environmental factors contribute to the shaping of a specific microbiota. Samples from thirty-nine juvenile angelsharks were collected from Las Teresitas nursery area in the Canary Islands over one year. Skin, oral and cloacal microbiomes were analysed using 16S rRNA gene amplicon sequencing. The sizes of individuals ranged between 24 and 42 cm in length. The shark microbiome was clearly distinct from the surrounding environment, indicating a unique composition from early life stages. Dominant bacteria present in the shark microbiomes included Vibrionaceae (up to 96%), Pseudoalteromonas (up to 63%), Rhodobacteraceae (up to 57%) and Alteromonadaceae (up to 20%). Seawater had a greater influence than sediment on the external skin microbiome, especially in younger individuals. This was not expected due to the burial behaviour of the species. Notably, the abundance of Pseudoalteromonadaceae (assessed by qPCR) was positively correlated with shark growth but was independent of the skin mucus. This suggests a protective role of this phylotype in younger individuals and may help in the adaptation to habitat conditions. This is the first comprehensive microbiome study in angelsharks, highlighting the importance of environmental preservation for microbial integrity and juvenile fitness.