Microbiota differences of native and invasive gelatinous zooplankton organisms in a low saline environment

The translocation of non-indigenous species around the world, especially in marine systems, is increasingly recognized as a matter of concern. Species translocations have been documented to lead to wide ranging changes in food web structure and functioning. Apart from direct effects of non-indigenous species, they can introduce novel bacteria as part of their microbiome to the new environment. For example, it has been shown that the fish pathogen Tenacibaculum maritimum, a gram-negative bacterium of the family Flavobacteriaceae, is a core microbiome member of the jellyfish species Pelagia noctiluca and Phialella quadrata. Similarly, other jellyfish microbiome members such as vibrio and flavo-bacteria have been identified causing potential harm to farmed fish. The Baltic Sea harbors many non-indigenous species, with most recent detection of the jellyfish Blackfordia virginica and the comb jelly Mnemiopsis leidyi in the low saline south-western Baltic Sea. This study is the first to make a comparative microbiome analysis of native and invasive gelatinous zooplankton species. Next generation 16S rRNA marker gene sequencing of the V1/V2 region has been employed to study bacterial microbiome composition, leading to 17K operational taxonomic units (OTUs). All tested species show significant differences in the OTU bacteria composition of their microbiomes (one way ANOSIM, R=1, P<0.008), with a dissimilarity between species of 85 to 92 %. The native jellyfish Aurelia aurita shows the highest bacterial OTU richness. The overall differentiation between microbiomes are driven by eight indicator bacteria OTUs, including Mycoplasma and Vibrio species. Those bacteria are especially problematic, as they include known pathogenic strains of importance for human health and aquaculture activities. Our results suggest that impact assessment of non-indigenous species should consider introduction of potential bacterial pathogens as part of their microbiomes. Holistic monitoring of invasive species could thus be crucial for risk assessments of aquaculture activities.