flatfish microbiota
Fish are colonized by a variety of microorganisms. The intestinal microbiota are  of particular importance, as they support digestion, nutrient uptake and play an important role in the immune system, development and reproduction. Flatfish live in close contact with the seafloor, and are particularly exposed to anthropogenic disturbances in the benthic environment such as bottom trawling. Sediment microbiota have been found to vary with fishing intensity, but we do not know whether this is also true for microbiota of marine holobionts, such as flatfishes. To better understand how the interplay between environmental factors and host traits shapes flatfish microbiota, we collected 162 individuals from three flatfish species (Buglossidium luteum, Limanda limanda and Pleuronectes platessa), across the southeastern North Sea. We characterized the intestinal microbiota using 16S rDNA metabarcoding, and evaluated the effects of various host traits (species, sex, age, weight, and condition factor) and environmental factors (sediment type and trawling intensity) on composition and diversity. OTU richness varied among species and changed with age, weight and sediment type. Additionally, community composition was dependent on species, age, condition factor and sediment type. Interestingly, we found that trawling intensity could also explain changes in intestinal microbial community composition, suggesting that the known impacts of bottom trawling on the benthic environment may indirectly influence the microbiota of flatfish. Our findings provide important insight into host-microbiota interactions in marine ecosystems and highlight the interplay between host traits and environment as drivers of intestinal microbial diversity and community composition in flatfish.