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Planktonic larvae (meroplankton) plays an important role in both benthic and pelagic ecosystems. The meroplankton study of South China Sea (SCS) and Philippine Sea (PS) may be particularly important, where they could serve as vectors for the influx of Pacific species into the East Indies Triangle (global marine biodiversity center). Here, we employed a metabarcoding method to investigate the geographical distribution pattern of meroplankton among SCS and PS. Different primers and reference databases were tested, for a better and more reliable interpretation of the current results and improvement of the method. In this study, metabarcoding was efficient for meroplankton study with high taxonomic resolution and good accuracy. COI against NCBI NT database showed the best taxonomy annotation efficiency, followed by 18S V1-V2, then 18S V4. The SILVA database showed similar performance to the NCBI NT database for the two 18S primers. The meroplankton diversity of SCS is higher than that of PS, and both communities are dominated by Polychaeta, Mollusca, Arthropoda and Echinodermata. Meroplankton geographical patterns are significantly different between the two basins, possibly due to the different distribution of their benthic adult, as well as the influence of five key environmental factors (IC, SCM, SST, SSS and DO). Our results suggest that the unidirectional Kuroshio Current intrusion may play an important role in shaping the biogeographical pattern in the west Pacific, by facilitating planktonic-larvae flowing into the northern SCS from the Pacific, on the contrary, limiting planktonic-larvae spreading out.

The Lianjiang coast in the East China Sea is a typical subtropical marine ecosystem, and shellfish cultivation occupies almost all of the available tidal flats. Many studies have investigated the effects of shellfish cultivation on benthic organisms and sediments, while the impact of shellfish cultivation on plankton ecosystems is still poorly understood. This study investigated the biogeographical patterns of microeukaryotic communities from Lianjiang coastal waters in four seasons using 18S ribosomal RNA gene amplicon sequencing. Microeukaryotes were mainly comprised of Dinoflagellata, Diatomea, Arthropoda, Ciliophora, Chlorophyta, Protalveolata, Cryptophyceae, and Ochrophyta, and presented significant differences in three habitats (the aquaculture area, confluent area, and offshore area) and four seasons. Similarity percentage analysis revealed that Paracalanus parvus, Heterocapsa rotundata, Bestiolina similis, and five additional key taxa contributed to spatio-temporal differences. Seasonal environmental and spatial factors explained 27.47% of microeukaryotic community variation on average, with 11.11% of the variation shared. Environmental variables, particularly depth, pH, and nitrite concentration, were strongly associated with the microeukaryotic community compositions. The neutral community model further demonstrated that stochastic processes were sufficient in shaping substantial variation in microeukaryotic communities across four seasons, which may reveal the remaining unexplained microeukaryotic community variation. We further divided four seasons into the aquaculture stages and non-aquaculture stages, and speculated that aquaculture activities may increase the dispersal limitation of microeukaryotes in coastal waters, especially for the big bodied-microbes like Arthropoda. The results provide a better understanding of the biogeographical patterns, processes, and mechanisms of microeukaryotic communities near shellfish cultivation. [ABSTRACT FROM AUTHOR]

The levels of chlorophyll a and nutrient concentrations in the surface waters of the western subtropical Pacific Ocean are among the lowest globally. In addition, our knowledge of basin-scale diversity and biogeography of microbial communities in this vast extremely oligotrophic environment is still rather limited. Here, high-throughput sequencing was used to examine the biodiversity and biogeography of abundant and rare microbial assemblages throughout the water column from the surface to a depth of 3,000 m across a horizontal distance of 1,100 km in the western Pacific Ocean. Microbial alpha diversity in the 200-m layer was higher than at other depths, with Gammaproteobacteria, Alphaproteobacteria, and Clostridia as the dominant classes in all samples. Distinctly vertical distributions within the microbial communities were revealed, with no difference horizontally. Some microbes exhibited depth stratification. For example, the relative abundances of Cyanobacteria and Alphaproteobacteria decreased with depth, while Nitrososphaeria, Actinobacteria, and Gammaproteobacteria increased with depth in the aphotic layers. Furthermore, we found that environmental (selective process) and spatial (neutral process) factors had different effects on abundant and rare taxa. Geographical distance showed little effect on the dispersal of all and abundant taxa, while statistically significant distance–decay relationships were observed among the rare taxa. Temperature and chlorophyll a were strongly associated with all, abundant, and rare taxa in the photic layers, while total inorganic nitrogen was recognized as the crucial factor in the aphotic layers. Variance partitioning analysis indicated that environmental selection played a relatively important role in shaping all and abundant taxa, while the variation in rare taxa explained by environmental and spatial processes was relatively low, as more than 70% of the variation remained unexplained. This study provides novel knowledge related to microbial community diversity in the western subtropical Pacific Ocean, and the analyzes biogeographical patterns among abundant and rare taxa. [ABSTRACT FROM AUTHOR]