Insight into the latitudinal gradient of biodiversity based on spatial variations in pelagic ciliate communities along the western Arctic Ocean

The latitudinal dynamics of biodiversity has been the focus of global attention. This study is based on the latitude gradient of biodiversity in the spatial changes of pelagic ciliate communities in the western Arctic Ocean. The gradient pattern of pelagic ciliate communities across four latitudes were investigated from the water surface at 22 sampling station in the northern Bering Sea of the western Arctic Ocean and Chukchi Sea from August 5 to August 24, 2016. Based on multivariate analyses, the results showed that (1) the spatial patterns of pelagic ciliates represented a significant latitudinal gradient along the western Arctic Ocean; (2) the species number and abundance of pelagic ciliate communities declined from 64°N to 80°N; (3) variations in the horizontal distribution of ciliates were significantly correlated with changes in physicochemical variables, especially water temperature and Chl a; Thus it is suggested that the expected latitudinal decline of biodiversity was evident along the western Arctic Ocean.

Use of a broad β-diversity measure of pelagic ciliate communities for assessing vertical heterogeneity of water columns in the Pacific Arctic Ocean

Multivariate dispersion has proven to be a broad β-diversity measure that shows the heterogeneity of environmental conditions. The dispersion patterns of pelagic ciliate communities were investigated at eight water depths in the northern Bering Sea of the western Arctic Ocean and Chukchi Sea. Multivariate analysis indicated that (1) pelagic ciliates showed significant variability in multivariate dispersion on a vertical scale, (2) dispersion patterns were shaped by both the species composition and individual abundance, (3) vertical variation in species occurrence was significantly related to nutrients and chlorophyll a, and (4) the dispersion measures at both species occurrence and species abundance resolutions were significantly negatively related to salinity and dissolved oxygen. This suggests that multivariate dispersion measures driven by both species composition and the individual abundance of pelagic ciliates may be a useful indicator of environmental heterogeneity in marine ecosystems.

Can pelagic ciliates indicate vertical variation in the water quality status of western Arctic pelagic ecosystems?

The vertical pattern of pelagic ciliate communities was observed at eight layers in the Chukchi Sea and the northern Bering Sea of the western Arctic Ocean during the summer sea-ice reduction period (August 5 to August 24, 2016). A total of 44 ciliate species were identified, with seven species dominated the communities in the water column. Multivariate and univariate analyses demonstrated that: (1) community structures of ciliates vary significantly among eight water depths; (2) variations in the vertical distribution of ciliates were significantly correlated with changes in physicochemical variables, especially the ammonia; (3) the distributions of the three dominant species were significantly and positively related to the chlorophyll a and ammonia concentrations; and (4) species richness and abundance were significantly and positively correlated with the concentrations of ammonia and chlorophyll a. These results suggest that pelagic ciliates may reflect vertical variations in the water quality status of western Arctic ecosystems.

Vertical shift in ciliate body-size spectrum and its environmental drivers in western Arctic pelagic ecosystems

As an inherent functional trait, body-size spectrum is widely used as an informative indicator to summarize community structures in taxon-free space. The vertical shift in the body-size spectrum of pelagic ciliates and its environmental drivers were explored at eight depth layers from the water surface to a depth of 100 m in western Arctic pelagic ecosystems. A total of 85 samples were collected at 23 sampling stations during the summer sea-ice reduction period from August 5 to August 24, 2016. Based on equivalent spherical diameter (ESD), six body-size ranks were identified, of which ranks S2 (15-25 μm), S3 (26-38 μm), S4 (39-60 μm), and S6 (79-91 μm) were the top four levels in frequency of occurrence and ranks S2 and S3 were the dominant levels in abundance. The body-size spectrum of the ciliates showed a clear vertical shift, with a significant succession among the dominant body-size units from the water surface to deeper layers in the water column. Multivariate analysis demonstrated a significant vertical variation in the body-size spectrum of the ciliates among the eight depths, which was significantly correlated with nutrients (phosphate and nitrite + nitrate) and chlorophyll a (Chl a), alone or in combination with dissolved oxygen. Four body-size diversity/distinctness indices were significantly correlated with the levels of phosphate, nitrite + nitrate, ammonium, and Chl a. Our results demonstrated that the body-size spectrum of pelagic ciliates can be shifted by environmental drivers (mainly nutrients and Chl a); thus, we suggest that it may be used to indicate water quality status on a vertical scale in the water column in deep seas.