Salinity structures the microbiome of the green seaweed Ulva

Abstract

The green seaweed, Ulva, is a model system to study seaweed–bacteria interactions, but the impact of environmental drivers on holobiont dynamics is little understood. In this study, we investigated Ulva-associated bacteria across the Atlantic–Baltic Sea salinity gradient, along a 2,000 km coastline with a total of 481 samples. Our results demonstrate that Ulva-associated bacterial composition was strongly structured by both salinity and host species, contradicting earlier statements that Ulva-associated bacterial communities are taxonomically highly variable across individuals and largely stochastically defined. Characteristic bacterial communities associated with distinct salinity regions may therefore facilitate the host’s adaptation across the environmental gradient.