Holistic pelagic biodiversity monitoring of the Black Sea via eDNA metabarcoding approach: From bacteria to marine mammals

As the largest semi-closed marine ecosystem in the world, the Black Sea has been heavily affected by human activities for a long time. Describing the biodiversity of multi-trophic biota in pelagic zone of the Black Sea and identifying the dominant environmental factors are prerequisites for protecting the sustainability of ecosystems. However, up to now, the taxonomic and distributional information about the Black Sea biota is not clear. Here, we employed a Tree-of-Life metabarcoding to analyze the biodiversity of eight communities in the Black Sea, investigated their biogeographical distribution, and further analyzed the influence of biological and abiotic factors on biota on large scales. We found that, (1) Over 8900 OTUs were detected in the Black Sea, of which 630 species were identified, covering the holistic biota from single-celled (bacteria 5620 OTUs 141 species; algae 1096 OTUs 185 species; protozoa 546 OTUs 146 species) to multicellular organisms (invertebrate metazoans 150 OTUs 34 species; fishes 1369 OTUs 76 species; large marine mammals 39 OTUs 5 species). (2) Higher trophic organisms (fishes and large mammals) distributed more evenly in space than the lower (microorganisms, protozoa and invertebrates). For lower trophic organisms, the vertical stratification was more obvious than the horizontal stratification (vertical p < 0.02, horizontal p < 0.05). (3) the bottom trophic organisms (bacteria and algae) of food web significantly affected distribution composition others through biological interactions (mantel (4) at level abiotic factors, effect local species sorting on communities was 15% higher than that mass dispersal effect. for first time, this study monitored profiled holistic biodiversity in pelagic zone black sea, provided technological advances preliminary knowledge ongoing sea ecosystem protection efforts.