In recent years, continuous coastal development has led to large-scale conversion of natural mudflats to aquaculture mudflats in intertidal zones, resulting in the loss of benthic biodiversity and alterations in community structure. However, systematic understanding of the differences in benthic biodiversity and community structure between aquaculture and natural mudflats, as well as their driving mechanisms—particularly large-scale spatial drivers—remains limited. This study focused on benthic ciliate communities in China’s intertidal aquaculture and natural mudflats. Using one-way analysis of variance (ANOVA), linear regression (LR), distance-based redundancy analysis (dbRDA), and variation partitioning analysis (VPA), we examined the differences in three dimensions of α-diversity (taxonomic, functional, and phylogenetic diversity) and community structure (species composition and functional composition) of benthic ciliates between the two types of mudflat, along with their driving factors. The results revealed that: ① no significant differences exist in local environmental variables between the two regions, indicating that aquaculture activities did not significantly modify habitat physicochemical conditions; ② significant differences existed in α-diversity, species composition, and functional composition of benthic ciliates between aquaculture and natural mudflats; ③ mean annual temperature (MAT) emerged as the primary driver of the observed differences in ciliate α-diversity and community structure. The results of this study demonstrate that large-scale climatic variables, rather than aquaculture impacts, are the key drivers of divergent patterns in benthic ciliate diversity and community structure between the two mudflat types. These findings provide critical insights for balancing intertidal mudflat aquaculture development with biodiversity conservation.
To evaluate the effects of the ecological restoration project involving Bolboschoenus maritimus in the Chongming Dongtan salt marsh wetland of the Yangtze River Estuary on the benthic community, this study employed principal coordinates analysis (PCoA), similarity percentage (SIMPER), and other methods to compare the community structure and diversity of benthic ciliates in the restoration area and the adjacent natural Bolboschoenus maritimus area over four consecutive seasons. The results are as follows: ① After restoration, the sediment median grain size, organic matter content, and ammonium levels in the restored area increased significantly; ② Significant differences were observed in the species composition of benthic ciliate communities between the restored and natural areas of Bolboschoenus maritimus. Salinity, phosphate, pH, oxidation-reduction potential, and meiofaunal biomass were the primary driving factors; ③ The α diversity of the benthic ciliate community in the natural area was significantly higher than that in the restored area. Silicate, salinity, ammonium, organic matter content, and sediment median grain size were the main factors influencing the diversity. In summary, the restored area exhibited a distinct benthic ciliate community composition and lower diversity compared to the natural area, suggesting that a longer recovery period may be needed for the sedimentary environment and benthic ciliate community in the restored area to reach the natural state.
The migration of freshwater harmful cyanobacteria into estuarine brackish waters poses a significant threat to local ecosystems. The different forms in which these cyanobacteria produce algal toxins, such as microcystins (MCs), can exert varying impacts on zooplankton communities. This study aimed to investigate the predominant forms of MCs produced by Microcystis in brackish waters and their subsequent effects on the survival and community composition of metazoan zooplankton. An in situ mesocosm experiment was conducted in a nearshore brackish wetland. Rectangular mesocosms (1.5 m depth, 150 L volume) were established in the open water area, filled with ambient wetland water filtered through a No. 25 plankton net, and inoculated with Microcystis colonies collected from Dianshan Lake to achieve an initial chlorophyll a concentration of 60 μg/L. The experiment included three replicate mesocosms and ran for 14 days. Data were processed using Microsoft Excel and statistically analyzed with SPSS 23.0. One-way analysis of variance (ANOVA) and t-tests were used to determine statistical significance. The survival of Microcystis and changes in microcystin forms (particulate vs. dissolved) were analyzed, alongside the effects of these toxin fractions on zooplankton abundance and community structure. The results demonstrated that Microcystis survived at a salinity of 4‰, with MCs predominantly existing in the intracellular (particulate) form. Within the mesocosms, intracellular microcystin concentrations initially increased and subsequently decreased, while the proportion of extracellular (dissolved) microcystins remained low (3%~8%) and presented a decreasing trend. Low salinity (≤7‰) appeared to promote intracellular microcystin synthesis. Conversely, both algal growth and intracellular microcystin synthesis were significantly inhibited when salinity was increased to 10‰, accompanied by a significant increase in microcystin release. Differential sensitivity and tolerance to MCs were observed among metazoan zooplankton groups. Particulate MCs were associated with slower-acting but longer-lasting toxicity, resulting in final zooplankton abundance significantly lower than initial levels, with copepods becoming proportionally more dominant in the community structure. In contrast, conditions favoring dissolved MCs led to substantial acute mortality, followed by a recovery phase where final abundance significantly exceeded initial levels, and rotifers emerged as the dominant group. These findings indicate that the partitioning of Microcystis toxins in brackish environments directly influences zooplankton abundance and community composition, thereby impacting the aquatic ecosystem. This research provides a crucial scientific basis for assessing the ecological risks of Microcystis toxins in brackish waters and for informing the development of effective water management strategies.
Coastal wetlands play an important role in the ecosystem. However, human activities such as pond aquaculture can alter their landscape patterns and biodiversity in the ecosystems. Environmental DNA (eDNA) technology can effectively reconstruct past biological communities and evaluate changes in biodiversity. In the present study, a sediment core was obtained from a wetland at the Doulonggang estuary in Yancheng, Jiangsu Province. By analyzing eDNA in the sediments and historical remote sensing images, in addition to performing 210Pb dating, the present study comprehensively explored how land use change affected biodiversity in the 2008–2023 period. 210Pb dating and historical remote sensing data showed that the sedimentary records included three phases of land use, including natural wetland (2008–2015), aquaculture ponds (2015–2019), and wetland restoration (2019–2023). eDNA in the sediments indicated that in the natural wetland phase, terrestrial herbaceous plants (26.69%~37.90%) and a brackish water community prevailed. In the aquaculture pond phase, the proportions of aquatic arthropods (such as Calanoida) and algae surged sharply, reflecting the ecological simplification caused by the artificial aquaculture system. In the wetland restoration phase, the proportion of diatoms (Bacillariophyta) increased to 89.04%, and the terrestrial herbs recovered gradually, indicating ecosystem restoration. The α-diversity index further confirmed that species diversity and evenness were the lowest when the area became an aquaculture pond in 2015 and then recovered gradually. The Bray-Curtis similarity index showed that there were significant differences in the biological composition among the three phases, with the main difference attributed to the proportion of diatoms. Therefore, this study shows that the ecological restoration project has enabled the wetland biological composition at the Doulonggang estuary to recover toward a natural wetland state. However, restoration of the ecosystem lags behind the landscape change, and long-term monitoring is necessary to promote the complete ecological restoration of the wetland. This study contributes to a deeper understanding of the dynamic change process of coastal wetland ecosystems under the interference of human activities and provides a scientific basis for ecological restoration and management of tidal flat wetlands.
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