Guangjian Xu

A multivariate approach to the determination of an indicator species pool for community-based bioassessment of marine water quality.

Previous studies in Chinese coastal waters of the Yellow Sea have shown that periphytic ciliates are reliable indicators of marine water quality. However, traditional community-based bioassessments are time-consuming because they rely on the identification and enumeration of all species within the community. In order to improve bioassessment efficiency, step-best-matching analysis was used to identify which are the most reliable indicator species among periphytic marine ciliate communities. Based on indices of species richness, diversity and evenness, a subset of 48 species (out of a total of 141) was found to retain sufficient information for accurately predicting water quality, and was more strongly related to changes of environmental variables than the full species set. These results demonstrate that the step-best-matching analysis is a powerful approach for identifying an indicator species pool from a full species dataset of a community, and allows the development of time-efficient sampling protocols for community-based marine bioassessment.

An approach to bioassessment of water quality using diversity measures based on species accumulative curves

Traditional community-based bioassessment is time-consuming because they rely on full species-abundance data of a community. To improve bioassessment efficiency, the feasibility of the diversity measures based on species accumulative curves for bioassessment of water quality status was studied based on a dataset of microperiphyton fauna. The results showed that: (1) the species accumulative curves well fitted the Michaelis-Menten equation; (2) the β- and γ-diversity, as well as the number of samples to 50% of the maximum species number (Michaelis-Menten constant K), can be statistically estimated based on the formulation; (3) the rarefied α-diversity represented a significant negative correlation with the changes in the nutrient NH4-N; and (4) the estimated β-diversity and the K constant were significantly positively related to the concentration of NH4-N. The results suggest that the diversity measures based on species accumulative curves might be used as a potential bioindicator of water quality in marine ecosystems.

Application of taxonomic distinctness indices of littoral macroinvertebrate communities for assessing long-term variation in ecological quality status of intertidal ecosystems, northern China

It has been increasingly recognized that taxonomic diversity indices have a number of desirable properties as an indicator for assessing ecological quality status, in particular their less sensitivity to natural habitat type and sampling effort but more to environmental stress and anthropogenic impact, and a statistical framework for the assessment of the significance of departure from expectation. Taxonomic patterns of macroinvertebrate fauna for assessing ecological quality status were studied based on six datasets collected from intertidal zones of the Yellow Sea, near Qingdao, northern China, during the period of 1989–1998. The invertebrate communities were sampled yearly at five stations with different bottom types during summer season (June). A total of 141 macroinvertebrate taxa were identified belonging 119 genera, 81 families, 34 orders, 19 classes, and 10 phyla. Multivariate analyses demonstrated that the taxonomic patterns of invertebrate fauna represented a significant variation in long-term temporal scale during the study period. The average taxonomic distinctness indices (Δ+) decreased to a significantly low level, while the variation in taxonomic distinctness measures (Λ+) increased to a significantly high level compared with the expected values from 1989 to 1998. The pairwise indices of Δ+ and (Λ+) showed a decreasing and increasing trend of departure from the expected taxonomic breadth in response to the environmental stress and anthropogenic impact, respectively. These results imply that the ecological quality status has been significantly deteriorated due to the increasing environmental stress and anthropogenic impact in intertidal zones of the Yellow Sea, northern China, and that the taxonomic distinctness indices of macroinvertebrate fauna are a robust indicator for evaluating ecological quality status.

Use of multivariate dispersion to assess water quality based on species composition data

Multivariate dispersion is a powerful approach to determine the variability in species composition of a fauna or a flora and has been considered as a broad β-diversity in global ecological research. To explore the availability of the dispersions based on species composition data for assessing water quality, a dataset of ciliated protozoa in a basin ecosystem, northern China, was studied. Samples were collected from five sampling stations, within a significant heterogeneity of environmental stress. The homogeneity of multivariate dispersions in species composition of the ciliate assemblages represented a clear spatial pattern in response to the environmental stress. Multivariate analysis demonstrated that the spatial variation in species composition of the ciliate was significantly correlated with the changes of environmental variables, especially the nutrients, in combination with the salinity and pH, or alone. Furthermore, the dispersion measure was found to be significantly related to the nutrient. Based on our data, we suggest that multivariate dispersion measures based on species presence/absence data might be used as a potential bioindicator of water quality in marine ecosystems.

Environmental drivers of heterogeneity in the trophic-functional structure of protozoan communities during an annual cycle in a coastal ecosystem

Trophic-functional groupings are an important biological trait to summarize community structure in functional space. The heterogeneity of the tropic-functional pattern of protozoan communities and its environmental drivers were studied in coastal waters of the Yellow Sea during a 1-year cycle. Samples were collected using the glass slide method at four stations within a water pollution gradient. A second-stage matrix-based analysis was used to summarize spatial variation in the annual pattern of the functional structure. A clustering analysis revealed significant variability in the trophic-functional pattern among the four stations during the 1-year cycle. The heterogeneity in the trophic-functional pattern of the communities was significantly related to changes in environmental variables, particularly ammonium-nitrogen and nitrates, alone or in combination with dissolved oxygen. These results suggest that the heterogeneity in annual patterns of protozoan trophic-functional structure may reflect water quality status in coastal ecosystems.

Sampling frequency of ciliated protozoan microfauna for seasonal distribution research in marine ecosystems.

Sampling frequency is important to obtain sufficient information for temporal research of microfauna. To determine an optimal strategy for exploring the seasonal variation in ciliated protozoa, a dataset from the Yellow Sea, northern China was studied. Samples were collected with 24 (biweekly), 12 (monthly), 8 (bimonthly per season) and 4 (seasonally) sampling events. Compared to the 24 samplings (100%), the 12-, 8- and 4-samplings recovered 94%, 94%, and 78% of the total species, respectively. To reveal the seasonal distribution, the 8-sampling regime may result in >75% information of the seasonal variance, while the traditional 4-sampling may only explain <65% of the total variance. With the increase of the sampling frequency, the biotic data showed stronger correlations with seasonal variables (e.g., temperature, salinity) in combination with nutrients. It is suggested that the 8-sampling events per year may be an optimal sampling strategy for ciliated protozoan seasonal research in marine ecosystems.

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.

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.

Identifying bioindicators across trait-taxon space for assessing water quality in marine environments

The response units of protozoan communities, based on a community-weighted mean (CWM) dataset across trait-taxon space, were investigated in order to determine their utility as bioindicators of marine water quality. From a total of 17 functional categories of seven biological traits, three functional response units (FRUs) were identified at correlation levels of >0.75. FRUs 1 and 3 generally dominated the communities in more polluted areas during warm seasons, while FRU2 appeared to prefer less polluted waters and dominated the communities in spring and winter. Correlation analysis demonstrated that the CWM values of FRUs 1 and 3 were significantly positively correlated to the concentrations of chemical oxygen demand (COD), whereas those of FRU2 were negatively correlated to COD. Across taxon-function space, 16 species were identified as potential bioindicators of water quality. These results suggest that redundancy analysis across trait-taxon space is a useful tool for identifying indicators of environmental quality.

Insights into bioassessment of marine pollution using body-size distinctness of planktonic ciliates based on a modified trait hierarchy.

Based on a modified trait hierarchy of body-size units, the feasibility for bioassessment of water pollution using body-size distinctness of planktonic ciliates was studied in a semi-enclosed bay, northern China. An annual dataset was collected at five sampling stations within a gradient of heavy metal contaminants. Results showed that: (1) in terms of probability density, the body-size spectra of the ciliates represented significant differences among the five stations; (2) bootstrap average analysis demonstrated a spatial variation in body-size rank patterns in response to pollution stress due to heavy metals; and (3) the average body-size distinctness (Δz(+)) and variation in body-size distinctness (Λz(+)), based on the modified trait hierarchy, revealed a clear departure pattern from the expected body-size spectra in areas with pollutants. These results suggest that the body-size diversity measures based on the modified trait hierarchy of the ciliates may be used as a potential indicator of marine pollution.