Are marine benthic microeukaryotes different from macrobenthos in terms of regional geographical distribution? New insights revealed by RNA metabarcoding

The Yellow Sea Cold Water Mass (YSCWM) is a unique hydrological phenomenon in the central Yellow Sea, resulting in different macrobenthos community compositions inside and outside the YSCWM. However, this pattern in benthic microeukaryotes has never been identified by morphological methods and DNA sequencing. To determine whether microeukaryotes differ from macrobenthos in terms of regional geographical distribution, we investigated the distribution of benthic microeukaryotes in the Yellow Sea using RNA metabarcoding. We identified a distinct distribution pattern of benthic microeukaryotes inside and outside the YSCWM, similar to that of macrobenthos. The community differentiation was likely attributable to the rare but unique OTUs, which accounted for approximately 31% of the total OTUs. Moreover, the sequence proportion of some abundant OTUs inside the YSCWM was also significantly different compared to that outside the YSCWM. Cluster analysis based on the microeukaryote communities clearly separated the Yellow Sea into different compartments. Similar pattern was also detected for the communities of abundant microeukaryotes, Diatomea, Fungi and Dinoflagellata. Variation partitioning analysis showed that spatial factors had stronger effects than environmental factors on shaping the distribution of the total, abundant and the top five dominant taxonomic groups, while environmental factors contributed more to regulating rare communities. This research indicates that the geographical distributions of marine benthic microeukaryotes and macrobenthos are similar, which can be shown by RNA sequencing.