Sun P., Wang Y., Laws E. and Huang B.Q.. 2020. Science of the Total Environment, 706:135753.

The relative importance of geographic distance and depth in shaping microeukaryote community composition on a regional scale remains unclear, especially how that composition is related to the movement of water masses. Here, we collected 156 water samples across the Taiwan Strait, which is characterized by complex topography and dynamic circulation, to investigate the composition of the ciliate community with high-throughput sequencing of the 18S rRNA gene transcript. Ciliate alpha diversity exhibited strong correlations with water chemistry, food abundance, and geographic distance; approximately 50% of the variance of the diversity could be explained by dissolved oxygen concentrations, chlorophyll a concentrations, bacterial abundance, and latitude. The sampling sites could be divided into three provinces based on the compositions of the ciliate communities, which exhibited a distinctly nonuniform spatial distribution pattern on a regional scale (587 km). Geographic distance, environmental conditions, and depth were identified as principal determinants of the ciliate community within the Strait. Geographic distance was the most influential factor. The effect of geographic distance seems to mainly reflect the movement of water masses that strongly constrain dispersal and contribute to environmental heterogeneity that accounts for 86.0% and 5.5%, respectively, of community valiance across the Strait. Overall, this study revealed that ciliate biogeography as a function of depth and environmental gradients is linked on a regional scale to the water masses that the ciliates inhabit. This result expands our knowledge of the drivers of microeukaryote community composition across regions within which there are water mass movements and strong spatial and environmental gradients.

Figure 1. (A) Map of Taiwan Strait highlighting the sampling sites and the distribution of water masses across depth strata in the present study; (B) five water masses identified based on properties of temperature and salinity. The lines across the panel B represent isodensity. Orange dots represent Coastal Diluted Water Mass (CDWM); blue dots represent South China Sea Water Mass (SCSWM); red dots represent Subsurface Kuroshio Branch Water Mass (SKBWM); green dots represent Upwelling Water Mass (UWM); purple ones represent Deep Water Mass (DWM).