Seasonal variability in taxonomic breadth of biofilm-dwelling ciliates in colonization surveys for marine bioassessment

An approach to evaluating seasonal responses to acute toxicity of antibiotic nitrofurazone on periphytic ciliated protist communities in marine environments

Periphytic protists including ciliates are the primary components of microbial communities in which they play a vital role in the progression of food webs by moving resources from lower to higher trophic levels. However, the toxic effects of veterinary antibiotics on periphytic protists across four seasons are minimally understood. Therefore, in this study, a 1-year survey was conducted with the antibiotic nitrofurazone (NFZ) applied at concentrations of 0.0, 1.5, 3.0, 6.0, and 12.0 mg/L. Samples of protist communities were collected using microscope glass slides during four seasons in the coastal waters of the Yellow Sea, Qingdao, northern China. The abundance of protists dropped with an increase in NFZ concentrations, and almost all species were dead at a concentration of 12.0 mg/L. The 12 h-LC50 values of NFZ for the protist biota were similar among the four seasons, despite significant seasonal variability in the community structure. The present results suggest that the periphytic protist biota may be used as a biomarker for assessing the ecotoxicity of NFZ in marine environments regardless of the year season.

Microplastics drive community dynamics of periphytic protozoan fauna in marine environments

The pollution of microplastics (MPs) to the marine environment has become a widespread focus of attention. To assess MP-induced ecotoxicity on marine ecosystems, periphytic protozoan communities were used as test organisms and exposed to five concentrations of MPs: 0, 1, 5, 25, and 125 mg l-1. Protozoan samples were collected using microscope slides from coastal waters of the Yellow Sea, northern China. A total of 13 protozoan species were identified and represented different tolerance to MP-induced ecotoxicity. Inhibition effects of MPs on the test protozoan communities were clearly shown in terms of both the species richness and individual abundance and followed linear relationships to MP concentrations. The community patterns were driven by MPs and significantly shifted at concentrations over 5 mg l-1. Our findings demonstrated that MPs may induce the community-level ecotoxic response of periphytic protozoan fauna and followed significant community dynamics. Thus, it is suggested that periphytic protozoan fauna may be used as useful community-based test model organisms for evaluating MP-induced ecotoxicity in marine environments.

Freshwater algal biofilm assemblages are more effective than invertebrate assemblages at aggregating microplastics

Microplastics, plastic particles less than 5 mm in length, are a ubiquitous pollutant in the environment, but research on freshwater microplastic contamination is lacking. A possible fate of microplastics in freshwater environments is to become entangled or aggregated in biofilms, which are matrices of algae, bacteria, and micro invertebrates that grow on underwater surfaces, following a progression of settling algae, periphyton, and finally invertebrate colonization. This in-situ study at the Oasis Marina at National Harbor in Oxon Hill, Maryland, examined how the taxonomic assemblages of freshwater biofilms in the Potomac River are associated with the number of microplastics aggregated within them. Aluminum discs, acting as artificial substrate for biofilm growth, were deployed at the water's surface and at 2 m depth to survey biofilm assemblage and were sampled monthly from October 2021-October 2022. Microplastic abundances in the water column were measured every 2 weeks over the same period. Spatial and temporal trends in trapped and suspended microplastics, water quality parameters (temperature, dissolved oxygen, pH, salinity, conductivity, turbidity, ammonia, nitrate, and phosphate), and biofilm assemblages were measured and compared to explore factors affecting the abundance of microplastics and their partitioning between the water column and biofilms. Water quality had no measurable impact on microplastic abundance in the water column at either depth, but temperature was negatively correlated to microplastic abundance in biofilms. As the weather warmed and biofilms progressed to invertebrate settling, they tended to contain fewer microplastics. This may have occurred because less biologically rich biofilms, primarily composed of unicellular algal colonies, provide a favorable surface for microplastic deposition. Understanding seasonal changes in biofilm assemblage and microplastic abundance may help track the fate of microplastics in freshwater systems, particularly in their interactions with lower trophic organisms.

Can salinity variability drive the colonization dynamics of periphytic protozoan fauna in marine environments?

To investigate effects of salinity variability on colonization dynamics of periphytic protozoan fauna, a 21-day study was conducted in temperature-controlled circulation systems (TCCSs). Periphytic protozoan communities were incubated using glass slides as artificial substrata in five TCCS aquaria with a large-scale salinity gradient of 9, 19, 29 (control), 39, and 49 PSU, respectively. The colonization dynamics were observed on days 3, 5, 7, 10, 14, and 21. The colonization dynamics were well fitted to the MacArthur-Wilson and logistic model equations in colonization and growth curves in all five treatments, respectively. However, the maximum species richness and abundance were reduced, and the colonization patterns were significantly shifted in four treatments with salinity changed by 20 PSU compared to the control (29 PSU). Thus, it is suggested that the large-scale salinity variability may reduce the species richness significantly and affect colonization dynamics of periphytic protozoan fauna in marine environments.

Insights into β-diversity of periphytic protozoan fauna along the water column of marine ecosystems

It has been increasingly recognized that there is high relevance in determining the β-diversity of communities along an environmental gradient for bioassessment of environmental quality status. To evaluate the vertical variations in β-diversity of periphytic protozoan fauna, in response to environmental heterogeneity in marine ecosystems, a baseline survey was conducted at the four water depths in the coastal waters of the Yellow Sea, northern China. Results demonstrated that (1) the species distribution presented different patterns at four water depths; (2) both compositional and community structure showed a significant vertical variation in multivariate dispersions from surface layer to the deeper layers; and (3) β-diversity measures generally increased from depths of 1 m to 5 m. These findings suggest that the homogeneity in the periphytic communities are of a high variability along the water column of marine ecosystems.

Seasonal variation in biological trait distribution of periphytic protozoa in coastal ecosystem: A baseline study for marine bioassessment

To reveal the seasonal variability in biological trait distribution for monitoring surveys based on periphytic protozoa, a baseline survey was carried out in a coastal region of Yellow Sea, northern China. A total of 40 slide samples were collected in a four season cycle after an exposure time period of 14 days. The results demonstrated that: (1) the community-weighted means (CWM) of algivores with large and medium sizes were high in spring and summer, while bacterivores with small size were high in autumn and winter; (2) there was a significant seasonal variation in the protozoan community functions, especially from spring/summer to autumn and winter; and (3) functional diversity indices generally peaked in spring or summer. Thus, there was a significant seasonal variation in protozoan community functions and this approach may be used to determine an optimal sampling strategy for monitoring programs in marine ecosystems.

Seasonal variability in biological trait pattern of biofilm-dwelling protozoa in colonization surveys for marine bioassessment

Biological trait analysis (BTA) has been proved to be a powerful tool to evaluate marine water quality. The species trait distributions of biofilm-dwelling protozoa were studied in a coastal region of the Yellow Sea, northern China, during a four-season cycle. The BTA demonstrated that: (1) the protozoa showed a significant seasonal variability in biological trait pattern during the colonization process across four seasons; (2) the colonization dynamics in species trait distribution followed different temporal models; (3) the functional dynamics in spring and summer were significantly different from those in autumn and winter (P < 0.05); and (4) functional diversity showed lower values in spring and summer than in autumn and winter. These findings suggest that BTA is subject to a high seasonal variability during colonization surveys when protozoa are used as bioindicators of marine water quality.

Seasonal variability in body-size spectrum of periphytic protozoa during colonization of artificial substrates for marine bioassessment

To identify the seasonal variability of body-size spectrum for monitoring surveys based on periphytic protozoa, a one-year baseline survey was carried out in a coastal region of Yellow Sea, northern China. A total of 240 glass slides were collected after immersion times of 3, 7, 10, 14, 21 and 28 days in a four season cycle, i.e., winter, spring, summer, and autumn. Body-size ranks S2 and S5 dominated the periphytic protozoan communities from the initial stage (from day 3) to the next periods in spring and autumn, while body-size ranks S7, S8 and S4 showed high variety at the equilibrium stages (from day 10) in summer and winter. The expectation analysis revealed that the samples had different patterns of departure from the anticipated body-size spectrum in each season. This study shows that an ideal sampling approach needs to be established when protozoa is used as bioindicators of marine water quality.