| As primary component of biofilm, periphytic ciliates with high diversity in taxonomy and function, play an important role in the structuring and functioning of microbial food webs, especially by importing bacteria, microalgae and other organic particles into benthos in many aquatic ecosystems. And with many advantages, they have widely been accepted as robust indicators to evaluate environmental stress and anthropogenic impact, especially in freshwater environments. We established and completed a series of methods in sampling, collecting and analyzing coastal periphytic ciliates communities by growing biofilm on an artificial substratum-glass slide. Based on these, a survey on periphytic ciliates was carried out during an annual cycle in four sites with a spatial gradient of environmental stress of coastal area near Qingdao, northern China, to investigate spatiotemporal patterns of periphytic ciliate community and their relationships with environmental conditions, potential in bioassessment, and biodiversity and ecosystem functioning in biofilm.The following conclusions are as follow:1) The temporal patterns of ciliate colonization had similar dynamics and were fitted to the MacArthur-Wilson and logistic models in colonization and growth curves at 1 and 3 m. The ciliate communities reached equilibrium in species composition within at least 10-days exposure time. However, they differed in both structural and functional parameters between the two layers, despite similar species composition. The species diversity, evenness, the colonization rate (G) and maximum abundance (Amax) were distinctly higher, but the time for reaching 90% equilibrium species number (T90%) was shorter at the depth of 1 m than those at a deeper layer.2) Sampling sizes represented a significant influence on biodiversity analysis of microperiphyton communities. Otherwise, more slide-replicates were required with increase of water depths and shortening colonization times for recovering species. Furthermore, to achieve< 10% standard errors,6 (105 cm2) and 9 (～160 cm2) slide-replicates were required for biodiversity analysis of the communities with various colonization times at depths of 1 m and 3 m during the summer season, respectively.3) For achieving a dissimilarity of<10%, more slide replicates were required with shortening community ages. The standard errors of four taxonomic relatedness indices due to the sample sizes were increased only in the young communities with shortening colonization times. For achieving a standard error of<10%,1 slide replicate was generally sufficient for the mature communities, whereas 4-10 were required for the young. These findings suggested that low slide replicates were required for measuring taxonomic relatedness indices compared to analyzing the community patterns.4) Enumeration time periods represented a strong influence on analyzing ecological features of microperiphyton communities, although no significant changes occurred in microperiphyton community structures between two enumeration schemes (within 24 h and 24-48 h) at both water depths. The delayed enumeration (within 24-48 h) may result in the similarity of the communities being reduced 5%-25%, and in the biodiversity (richness, evenness, and diversity of species) indices decreasing with shortening community ages. These results suggest that the enumeration should be completed as soon as possible within 24 h after sampling to analyze ecological features of microperiphyton communities5) Enumeration time periods (within 24 h and 24-48 h after sampling) represented a strong influence on analyzing both colonization and taxonomic relatedness features of periphytic ciliate communities, although no significant changes occurred in colonization patterns between two enumeration schemes. The delayed enumeration (within 24-48 h) may result in the species richness, individual abundance, colonization rate decreasing to standard errors of>10% in samples with almost all colonization ages, and in the similarities of the communities reducing to 11%-38%. However, the species biodiversity (e.g., species diversity and evenness, except species richness) and taxonomic relatedness (taxonomic diversity, taxonomic distinctness and average taxonomic distinctness, except variation in taxonomic distinctness) measures of periphytic ciliate communities were weakly sensitive to disturbance from the delayed enumeration, achieving standard errors of<10% and<5% during the colonization periods, respectively. These results suggest that the enumeration should be completed as soon as possible within 24 h after sampling.6) According to the probability of recovering those species with a specified cumulative contribution to communities, the optimal sample-size for evaluating biofilm-dwelling ciliate colonization increases with shortening exposure time. More slide-replicates were required at a depth of 3 m than at 1 m.10 slide-replicates (175 cm2) were sufficient to achieve a 95% probability of recovering those species with a cumulative contribution of> 90% to the ciliate communities at a depth of 1 m. These results suggest that ten slide-replicates immersed at a depth of 1 m may be an optimal sampling strategy for analyzing the colonization dynamics of biofilm-dwelling ciliate communities in marine habitats.7) Environmental variables of the four sampling sites during a one-year cycle showed that concentrations of soluble reactive phosphate (SRP), nutrients ammonium nitrogen (NH4-N), nitrate nitrogen (NO3-N), and nitrite nitrogen (NO2-N) were generally higher at sites A (Hudao), and B (Lundu) and lower at sites C (Zhongyuan) and D (Aofan), as well as chemic oxygen damends (COD).8) The species number was stable except in winter, and the relative compostions in taxomation, ecological type and trophic function type were mostly stable in the one-year cycl; the average of turnover rate was ～0.30; the abundance and biomass peaked in autumn, especially in September, and was lowest in winter; based on the similarity, the periphytic ciliate communities from ten monthes formed three groups:A (December and January), B (April, May, June, and July) and C (August, September, October and November).9) A total of 144 ciliate species representing 78 genera,43 families,19 orders and 8 classes were recorded during the one-year investigation in mature communities (14 days). Among these species,31 distributed in all four seasons, while 11,11,13 and two forms occurred only in spring, summer, autumn and winter season, respectively. The species number and total abundance peaked in spring and autumn, with minimum values in winter. Ciliate community structures differed significantly between seasons, and were significantly correlated with the changes in environmental variables, especially temperature, pH, dissolved oxygen (DO) and the nutrients. Of 36 dominant species (top 15 ranked contributors in each season), nine (e.g., Pseudovorticella paracratera, Trochilia minuta, and Zoothamnium sp.) were significantly correlated with pH, DO or nutrients. Species richness (D’), evenness (J’) and diversity (H’) measures were significantly correlated with temperature, pH, DO or soluble reactive phosphates. Results demonstrated that periphytic ciliates exhibited a clear seasonal variation in community structures in response to environmental conditions and potentially might be used as a robust bioindicator for assessing environmental quality status in coastal waters.10) The ability of biofilm-dwelling ciliate communities for assessing environmental quality status was studied, using glass slides as an artificial substratum, during a one-year cycle. Results showed that:(1) the community structures of the ciliates represented significant differences among the four sampling stations; (2) spatial patterns of the ciliate communities were significantly correlated with environmental variables, especially COD and the nutrients; (3) five dominant species (Hartmannula angustipilosa, Metaurostylopsis sp.1, Discocephalus ehrenbergi, Stephanopogon minuta and Pseudovorticella paracratera) were significantly correlated with nutrients or COD; and (4) the species richness measure was significantly correlated with the nutrient NO3-N. It is suggested that biofilm-dwelling ciliate communities might be used as a potentially robust bioindicator for discriminating environmental quality status in coastal waters.11) To determine the feasibility of using a small species pool from a raw dataset of biofilm-dwelling ciliates for bioassessment based on taxonomic diversity, a 33-species subset was identified from the raw 144-species dataset using a multivariate method. The spatial patterns of this subset were significantly correlated with the changes in the nutrients and chemical oxygen demand. The taxonomic diversity indices were significantly correlated with nutrients. The pair-wise indices of average taxonomic distinctness and the variation in taxonomic distinctness showed a clear departure from the expected taxonomic pattern. These findings suggest that this small ciliate assemblage might be used as an adequate species pool for discriminating water quality status based on taxonomic distinctness in marine ecosystems.12) The feasibility for developing a protocol to assess marine water quality based on early colonization features of periphytic ciliate fauna was studied by collecting ciliate communities with 3-28-day ages monthly at four stations with a spatial gradient of environmental stress. The spatial patterns of both early (3-7 days) and mature (>10 days) communities of the ciliates represented significant differences among the four stations, and were significantly correlated with environmental variables, especially nutrients and chemical oxygen demand (COD). Seven and eight dominant species were significantly correlated with nutrients or COD within the early and mature communities, respectively. The species richness indices were strongly correlated with nutrients, especially in mature communities. These findings suggest that it is possible to assess the status of water quality using early colonization features of periphytic ciliate fauna in coastal waters... |
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