Influence of enumeration time periods on analyzing colonization features and taxonomic relatedness of periphytic ciliate communities using an artificial substratum for marine bioassessment

Progress in 'taxonomic sufficiency' in aquatic biological investigations

The 'taxonomic sufficiency' (TS) approach has been applied to algae, protists, invertebrates, and vertebrates, generally by aggregating species-level abundance data to a higher taxonomic level, where genus-level data are often highly correlated with species-level data and are a valid proxy level. The TS approach offers the possibility of a comparison of data from different geographical areas and highlights the effects of contaminants. The TS approach is stable in the face of different researchers and in the comparison of long-term biological survey data. The effectiveness of the TS approach may increase with increasing environmental gradients or spatial area. The TS approach should be avoided when the spatial area is small and small differences in species-level data are considered important, so as not to cancel out the distribution patterns specific to the local environment of the biological taxa.

Use of functional units of periphytic protozoa for monitoring water quality in marine ecosystems: bioindicator redundancy

Although periphytic protozoan communities have long been used for the bioassessment of water quality, their utility is hampered by functional redundancy, leading to high "signal-to-noise" ratios. In this study, a 1-year baseline survey of periphytic protozoan communities was carried out in coastal waters of the Yellow Sea, northern China, in order to determine redundancy levels in conditions of differing water quality. Samples were collected at four sampling sites along a pollution gradient. Environmental variables such as salinity, chemical oxygen demand (COD), and concentrations of dissolved oxygen (DO), soluble reactive phosphates (SRP), ammonium nitrogen (NH4-N), and nitrate nitrogen (NO3-N) were measured to compare with biotic factors. A total of 53 functional units (FUs) were identified from 144 observed protozoan species based on four biological traits, i.e., feeding type, body size, movement type, and source of food supply. For reducing the "signal-to-noise" ratios of species-abundance/biomass data, the peeling procedure was used to identify the bioindicator redundancy levels based on these FUs. Three consecutive subsets of response units (RU1-RU3) with correlation coefficients > 0.75 of the full FU dataset were identified, comprising 12 FUs, 21 FUs, and 9 FUs, respectively. Algivores and bacterivores were dominant in RU1 and RU2 among the polluted sites, whereas raptors were dominant in RU3 at the unpolluted site. In terms of relative abundance, RU1 was the primary contributor to the protozoan communities during the 1-year cycle and its relative abundance increased with the increasing pollution, whereas RU2 and RU3, with complementary temporal distributions, generally decreased with increasing pollution. Ordinations based on bootstrapped average analyses revealed a significant variation in the functional pattern of all three RUs among the four sampling sites. Biological-environmental match analysis demonstrated that the variability was driven by the increasing concentrations of nutrients (e.g., NH4-N, NO3-N, and PO4-P) and decreasing concentrations of DO (P < 0.05). There were high levels of functional redundancy among periphytic protozoan communities which could be used as bioindicators of marine water quality.

Trophic-functional patterns of biofilm-dwelling ciliates at different water depths in coastal waters of the Yellow Sea, northern China

Vertical variations in trophic-functional patterns of biofilm-dwelling ciliates were studied in coastal waters of the Yellow Sea, northern China. A total of 50 species were identified and assigned to four trophic-functional groups (TFgrs): algivores (A), bacterivorous (B), non-selective (N) and raptors (R). The trophic-functional structures of the ciliate communities showed significant variability among different water depths: (1) with increasing water depth, relative species numbers and relative abundances of groups A and R decreased sharply whereas those of groups B and N increased gradually; (2) in terms of the frequency of occurrences, group A dominated at depths of 1-3.5 m whereas group B dominated at 5 m, while in terms of the probability density function of the trophic-functional spectrum, group A was the highest contributor at 1 m and group B was highest at the other three depths; (3) distance-based redundancy analyses revealed significant differences in trophic-functional patterns among the four depths, except between 2 and 3.5 m (P > 0.05); and (4) the trophic-functional trait diversity increased from 1 to 3.5 m and decreased sharply at 5 m. Our results suggest that the biofilm-dwelling ciliates maintain a stable trophic-functional pattern and high biodiversity at depths of 1-3.5 m.

An approach to analyzing environmental drivers to spatial variations in annual distribution of periphytic protozoa in coastal ecosystems

The environmental drivers to the spatial variation in annual distribution were studied based on an annual dataset of periphytic protozoa using multivariate approaches. Samples were monthly collected at four stations within a pollution gradient in coastal waters of the Yellow Sea, northern China during a 1-year period. The second-stage (2STAGE) analyses showed that the internal patterns of the annual distribution were changed along the pollution gradient in terms of abundance. The dominant species represented different succession dynamics among four sampling stations during a 1-year cycle. Best matching analysis demonstrated that the spatial variations in annual distribution of the protozoa were significantly correlated with ammonium nitrogen (NH4-N), alone or in combination with salinity and dissolved oxygen (DO). Based on the results, we suggest that the nutrients, salinity and DO may be the main drivers to shape the spatial variations in annual distribution of periphytic protozoa.

An approach to determining functional parameters of microperiphyton fauna in colonization surveys for marine bioassessment based on rarefaction curves

The functional parameters, i.e., the estimated equilibrium species number (S eq), the colonization rate constant, and the time taken to reach 90 % of S eq (T 90), of microperiphyton fauna have been widely used to determine the water quality status in aquatic ecosystems. The objective of this investigation was to develop a protocol for determining functional parameters of microperiphyton fauna in colonization surveys for marine bioassessment based on rarefaction and regression analyses. The temporal dynamics in species richness of microperiphyton fauna during the colonization period was analyzed based on a dataset of periphytic ciliates in Chinese coastal waters of the Yellow Sea. The results showed that (1) based on observed species richness and estimated maximum species numbers, a total of 16 glass slides were required in order to achieve coefficients of variation of <5 % in the functional parameters; (2) the rarefied average species richness and functional parameters showed weak sensitivity to sampling effort; (3) the temporal variations in average species richness were well-fitted to the MacArthur-Wilson model; and (4) the sampling effort of ~8 glass slides was sufficient to achieve coefficients of variation of <5 % in equilibrium average species number (AvS eq), colonization rate (AvG), and the time to reach 90 % of AvS eq (AvT 90) based on the average species richness. The findings suggest that the AvS eq, AvG, and AvT 90 values based on rarefied average species richness of microperiphyton might be used as reliable ecological indicators for the bioassessment of marine water quality in coastal habitats.

An approach to detecting species diversity of microfaunas in colonization surveys for marine bioassessment based on rarefaction curves

The objective of this study was to measure α-, β- and γ-diversity of microfaunas with different ages in colonization surveys using rarefaction-modeling methods. A dataset was complied based on a microperiphyton survey in coastal waters of the Yellow Sea, near Qingdao. The analyses showed that: (1) there was a strong residual influence of sampling effort on β- and γ-diversity after rarefaction, especially for the young communities; (2) the rarefaction curves were well fitted to the Michaelis-Menten equation, and allow modeling and removing the residual influence of sampling effort on β- and γ-diversity; and (3) the estimated values of α-, β- and γ-diversity of a community based on the rarefaction-modeling method were independent of the influence of sampling effort. The results suggest that this approach may be used as a feasible tool to detect α-, β- and γ-diversity without the influence of sampling effort in microfauna colonization surveys for marine bioassessment.

Do early colonization patterns of periphytic ciliate fauna reveal environmental quality status in coastal waters?

The feasibility for developing a protocol to assess marine water quality based on early colonization features of periphytic ciliate fauna was studied in coastal waters of the Yellow Sea, northern China. The ciliate communities with 3-28-day ages were collected monthly at four stations with a spatial gradient of environmental stress from August 2011 to July 2012. 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.

Use of biofilm-dwelling ciliate communities to determine environmental quality status of coastal waters

It has increasingly been recognized that the ecological features of protozoan communities have many advantages as a favorable bioindicator to evaluate environmental stress and anthropogenic impact in many aquatic ecosystems. The ability of biofilm-dwelling ciliate communities for assessing environmental quality status was studied, using glass slides as an artificial substratum, during a 1-year cycle (August 2011-July 2012) in coastal waters of the Yellow Sea, northern China. The samples were collected monthly at a depth of 1m from four sampling stations with a spatial gradient of environmental stress. Environmental variables, e.g., salinity, dissolved oxygen (DO), chemical oxygen demand (COD), nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N) and soluble reactive phosphates (SRP), were measured synchronously for comparison with biotic parameters. 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.

Functional groups of marine ciliated protozoa and their relationships to water quality

Ciliated protozoa (ciliates) play important ecological roles in coastal waters, especially regarding their interaction with environmental parameters. In order to increase our knowledge and understanding on the functional structure of ciliate communities and their relationships to environmental conditions in marine ecosystems, a 12-month study was carried out in a semi-enclosed bay in northern China. Samples were collected biweekly at five sampling stations with differing levels of pollution/eutrophication, giving a total of 120 samples. Thirteen functional groups of ciliates (A-M) were defined based on their specific spatio-temporal distribution and relationships to physico-chemical parameters. Six of these groups (H-M) were the primary contributors to the ciliate communities in the polluted/eutrophic areas, whereas the other seven groups (A-G) dominated the communities in less polluted areas. Six groups (A, D, G, H, I and K) dominated during the warm seasons (summer and autumn), with the other seven (B, C, E, F, J, L and M) dominating in the cold seasons (spring and winter). Of these, groups B (mainly aloricate ciliates), I (aloricate ciliates) and L (mainly loricate tintinnids) were the primary contributors to the communities. It was also shown that aloricate ciliates and tintinnids represented different roles in structuring and functioning of the communities. The results suggest that the ciliate communities may be constructed by several functional groups in response to the environmental conditions. Thus, we conclude that these functional groups might be potentially useful bioindicators for bioassessment and conservation in marine habitats.