The seaweed production industry is rapidly expanding worldwide. The green seaweed Ulva is increasingly recognized as an excellent sustainable feedstock, due to its high growth rates, its wide tolerance to environmental conditions, and its potential in bioremediation and integrated multi-trophic aquaculture. Seaweed associated microbes could play an important role in the optimization of the Ulva-crop-system, by increasing host growth, changing biochemical composition, and fending off pathogens that cause disease. In order to be successfully implemented, however, microbiota manipulation requires fundamental knowledge on the successional dynamics of the cultivated Ulva microbiome. In this study, we monitored the dynamics of Ulva-associated bacterial communities over a time-period of eleven months, from the nursery phase and outplanting in the field up to the harvest. We compared microbial dynamics in land-based tanks and an offshore seafarm, as well as natural populations of Ulva fenestrata and Ulva linza. Our results showed that Ulva hatchlings in the nursery phase harboured a distinct microbiome compared to outplanted Ulva. The hatchling communities were dominated by 1–3 genera, several of which have been identified as growth-promoting bacteria before (e.g., Sulfitobacter, Algitalea). In addition, we found that the nursery conditions played a larger role in the microbiome composition than host specificity, suggesting that the nursery environment is a crucial microbial source pool. The bacterial composition underwent a swift transformation following outplanting, differing significantly from the nursery samples within only seven days. Our results demonstrated that the bacterial communities in the nursery phase remain susceptible to newly introduced microbiota. Controlled nursery conditions could therefore provide the ideal opportunity for microbiota manipulation, but the acquired microbes might not endure the transition to open-water conditions. |
