Seasonal variability in trophic-functional patterns of marine biofilm-dwelling ciliates during the process of colonization

In order to evaluate the seasonal shifts of colonization dynamics in trophic-functional groups of biofilm-dwelling ciliates, a one-year baseline survey was carried out in Chinese coastal waters of the Yellow Sea. Utilizing glass microscope slides as artificial substrates, a total of 240 slides were used to collect ciliates after immersion times of 3, 7, 10, 14, 21 and 28 days during each of four seasons, i.e., February, May, August and November, 2017 representing winter, spring, summer, and autumn, respectively. Four trophic-functional groups (TFgrs) were recorded from a 122 species-dataset, i.e., algivores (A), non-selectives (N), raptors (R) and bacterivores (B), comprising of 65, 31, 12 and 14 species, respectively. Based on these four TFgrs, the colonization dynamics of biofilm-dwelling ciliates exhibited different seasonal patterns in terms of both frequency of occurrence and probability density during the study period. During colonization processes, TFgrs A, N and B occurred frequently and generally dominated the samples following an increase in abundance of their members from spring to autumn, whereas TFgr R generally showed different colonization dynamics during the four seasons. Distance-based redundancy analysis (dbRDA) demonstrated that the colonization dynamics of the trophic-functional groups followed different models in each of the four seasons. Multidimensional scaling ordinations (MDS) based on bootstrapped-average analyses revealed a clear shift in dominance of trophic-functional groups from spring to winter. Thus, the colonization feature of biofilm-dwelling protozoa as measured by trophic-functional structure differed seasonally, suggesting that an optimal sampling strategy needs to be developed when using ciliates as bioindicators on marine water quality.