Cultivated kelp microbiome

Kelp are important primary producers and are colonized by diverse microbes which have both positive and negative effects on their hosts. The kelp microbiome could potentially support the burgeoning kelp cultivation sector by improving host growth, stress tolerance, and resistance to disease. Fundamental questions about the cultivated kelp microbiome still need to be addressed before microbiome-based approaches can be developed. A critical knowledge gap is how the cultivated kelp microbiome develops as the host grows and how different abiotic conditions and microbial source pools affect the microbiome. In this study we tested whether microbes that colonize kelp in the hatchery stage persist and shape kelp microbiome succession over time at open ocean cultivation sites. We outplanted two species of kelp, Alaria marginata and Saccharina latissima, originating from the same hatchery to multiple cultivation sites to test the stability of the cultured kelp microbiome when exposed to different abiotic conditions and microbial communities. We showed the kelp microbiome in the hatchery is distinct from the microbiome of outplanted kelp. We identified bacteria that persisted on kelp following outplanting and provide novel evidence that the hatchery stage is a viable target for manipulating the kelp microbiome. Significant host species-specific microbiome differences were observed throughout the cultivation process. The microbiome of cultivated kelp showed consistent successional dynamics despite differences in host species or microbial source pools. Differences associated with month of sampling were greater than differences between cultivation sites, indicating seasonal changes in host or abiotic factors drive microbiome turnover in cultivated kelps.