Effects of fish farming on phytoplankton community under the thermal stress caused by a power plant in a eutrophic, semi-enclosed bay: induce toxic dinoflagellate (Prorocentrum minimum) blooms in cold seasons

Diversity and distribution analysis of eukaryotic communities in the Xiangshan Bay, East China sea by metabarcoding approach

Eukaryotic communities play an important role in the coastal ecosystem of Xiangshan Bay, a narrow semi-closed bay famous for fisheries and marine farming. However, information on the diversity and composition of eukaryotic communities in Xiangshan Bay remains unclear. In this study, the metabarcoding approach was utilized to comprehensively investigate the eukaryotic plankton community structure and dominant taxa, particularly eukaryotic microalgae, in the Xiangshan Bay over a period of four months in 2018. The results showed that the three major phyla were Arthropoda, Chlorophyta, and Bacillariophyta. The richness indices revealed that species richness peaked in February and was at its lowest in May. Diversity indices showed that the samples collected in May had the lowest diversity. Centropages was detected in the samples of all months, however, its highest dominance was observed in the samples collected in February. In addition, compared to other months, a greater proportion of eukaryotic microalgae was witnessed in March. The three eukaryotic algae with highest abundances in March were Cyclotella, Prorocentrum, and Thalassiosira. Moreover, high diversity of pico-sized (0.2-2.0 μm) phytoplankton (which are often easily missed by microscopy) was discovered in this study by using metabarcoding approach. This study highlights the strength and significance of the metabarcoding approach to uncover a large number of eukaryotic species which remains undetectable during application of conventional approaches. The findings of this study reveals that the eukaryotic community structure varies noticeably in both time and space throughout sampling period, with temperature being the most important environmental factor influencing these changes. This study lays a solid foundation to understand eukaryotic plankton composition, temporal and spatial dynamics and the distribution mechanism of eukaryotic plankton community in Xiangshan Bay, providing theoretical reference for further studies related to marine ecology.

Impacts of Thermal Drainage on Bacterial Diversity and Community Construction in Tianwan Nuclear Power Plant

As one of the low-carbon and high-efficient energy sources, nuclear power is developing vigorously to alleviate the crisis of global climate warming and realize carbon neutrality goals. Meanwhile, the ecological effect of thermal drainage in the nuclear power plant is significantly remarkable, which environmental assessment system has not yet referred to microorganisms. The rapid response of microbial diversity and community structure to environmental changes is crucial for ecosystem stability. This study investigated the bacterial diversity, community construction, and the co-occurrence patterns by 16S rRNA gene amplicon sequencing among gradient warming regions in Tianwan Nuclear Power Plant. The alpha diversity of the high warming region was the lowest in summer, which was dominated by Proteobacteria, whereas the highest bacterial diversity presented in high warming regions in winter, which harbored higher proportions of Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes. The spatial distribution of bacterial communities showed clear separation especially in summer. Strong correlations were between community compositions and environmental factors, such as salinity, DO, TN, and temperature in summer. Furthermore, remarkable seasonality in bacterial co-occurrence patterns was discovered: the robustness of the bacterial co-occurrence network was promoted in winter, while the complexity and robustness were decreased in summer due to the warming of thermal drainage. These findings reveal the potential factors underpinning the influence of thermal drainage on bacterial community structure, which make it possible to predict the ecological effect of the nuclear power plants by exploring how the microbial assembly is likely to respond to the temperature and other environmental changes.

Spatiotemporal variation of phytoplankton communities and water quality among seaweed, shellfish and cage fish culture systems

Various marine aquaculture systems have different impacts on the environment, but few assessments were focused on the environmental impact by different systems in the same region. To study the effects of various aquaculture systems on phytoplankton community structure and water properties, 5 surveys were carried out in seaweed (Gracilaria lemaneiformis, GL), shellfish (Mytilus coruscus, MC) and cage fish (Larimichthys crocea, LC) mariculture areas in Dongji island, Zhejiang, China from June to September 2020. Significant differences were observed in some environmental parameters and phytoplankton communities among three aquaculture systems. The dissolved oxygen concentrations and Secchi depth in the surface waters in GL area were relatively higher than in the blank and other areas. As for nutrients concentration, LC and MC areas had higher concentrations than blank area, while GL area was the lowest. Though Chlorophyll-a concentration displayed fluctuations, relatively lower concentrations were found in GL area. Shannon diversity index was found to be relatively constant and higher in GL area. The Non-metric multidimensional scaling results revealed that phytoplankton composition had a distinct pattern among sampling times. The correlations and Redundancy analysis showed that total nitrogen, salinity and transparency were primary environmental factors associated with phytoplankton composition. Our study confirmed that different marine aquaculture systems can cause environmental fluctuations. Among the three systems, seaweed cultivation can bring multiple positive effects by improving surrounding water quality and increasing the phytoplankton composition. G. lemaneiformis culture in summer has great positive impact on seawater environment as it can maintain the ecological balance and reduce the risk of harmful algal blooms (HABs), and therefore, it is strongly recommended more G. lemaneiformis cultivation in this region in summer.

Contrasting Mechanisms Determine the Microeukaryotic and Syndiniales Community Assembly in a Eutrophic bay

Syndiniales is a diverse parasitic group, increasingly gaining attention owing to its high taxonomic diversity in marine ecosystems and inhibitory effects on the dinoflagellate blooms. However, their seasonal dynamics, host interactions, and mechanisms of community assembly are largely unknown, particularly in eutrophic waters. Here, using 18S rRNA gene amplicon sequencing, we intended to elucidate the interactions between Syndiniales and microeukaryotes, as well as community assembly processes in a eutrophic bay. The results showed that Syndiniales group II was dominating throughout the year, with substantially higher abundance in the winter and spring, whereas Syndiniales group I was more abundant in the summer and autumn. Temperature and Dinoflagellata were the most important abiotic and biotic factors driving variations of the Syndiniales community, respectively. The assembly processes of microeukaryotes and Syndiniales were completely different, with the former being controlled by a balance between homogeneous selection and drift and the latter being solely governed by drift. Network analysis revealed that Syndiniales group II had the largest number of interactions with microeukaryotes, and they primarily associated with Dinoflagellata in the winter, while interactions with Chlorophyta and Bacillariophyta increased dramatically in summer and autumn. These findings provide significant insights in understanding the interactions and assembly processes of Syndiniales throughout the year, which is critical in revealing the roles of single-celled parasites in driving protist dynamics in eutrophic waters.

Phytoplankton community structure changes during autumn and spring in response to environmental variables in Methana, Saronikos Gulf, Greece

Phytoplankton community was investigated during two contrasting periods using offshore plankton samples in the volcanic area of Methana peninsula (Saronikos Gulf): the first at early autumn (warm period, September 2016) and the second one at early spring (cold period, March 2017). In order to investigate the phytoplankton community structure in the complex geo-biochemical conditions of the area, samples were collected from stations near the CO₂ hydrothermal vents, at the hydrothermal sulfur and radioactive springs and at a fishery nearby Methana town. Three major phytoplankton groups, Bacillariophyceae, Dinophyceae, and Prymnesiophyceae, were studied, using inverted microscopy. In early autumn, Dinophyceae were dominant in the majority of the stations with cell concentrations of Prorocentrum spp. up to ~ 35.5 × 10³ cells l^-1. In early spring, the dominant class was Bacillariophyceae with dominant genus Nitzschia/Pseudo-nitzschia presenting cell concentrations up to ~ 33.9 × 10³ cells l^-1. Furthermore, Prymnesiophyceae appeared in both spring and autumn samples with small fluctuations. Total phytoplankton cell concentrations followed a seasonal trend, presenting slightly lower values in the hydrothermal-effected area in comparison with the broader Saronikos Gulf, confirming the prevalence of oligotrophic conditions. Seasonal variation was very strong, revealing an association with water temperature and nutrient content. Those environmental variables proved to have a strong effect that was reflected in the phytoplankton community structure.

Phytoplankton composition and abundance as indicators of aquaculture effluents impact in coastal environments of mid Gulf of California

Composition and abundance of phytoplankton in two areas of Gulf of California, one near (ND) and one far (FD) from shrimp farms discharge, were studied in 3 seasons: late fall (farms finishing operations); spring (farms not operating); and summer (farms operating). In ND, 61 diatoms, 33 dinoflagellates, 4 cyanobacteria, and 2 silicoflagellates were identified; in FD, 72 diatoms, 38 dinoflagellates, 5 cyanobacteria, and 4 silicoflagellates were found. Thirty-three species were recorded only in ND (20 diatoms, 11 dinoflagellates, 1 silicoflagellate), whereas 39 species appeared exclusively in the FD (28 diatoms, 9 dinoflagellates, 1 cyanobacteria, 1 silicoflagellate). Thirty-seven species were common for both areas (23 diatoms, 10 dinoflagellates, 3 cyanobacteria and 1 silicoflagellate). In ND, 9 species potentially toxic (3 diatoms, 5 dinoflagellates, 1 cyanobacteria) were identified. From FD, 3 species potentially toxic (2 diatoms and 1 cyanobacteria) were found. Total abundance of phytoplankton was more than double in ND than in FD. The species richness and diversity, were greater in FD. Higher phytoplankton abundance was observed when farms were operating or finishing operations. The composition and abundance of phytoplankton is a good indicator of shrimp effluents impact, diminishing the species richness and diversity, but augmenting the abundance.

Water-lifting aerator reduces algal growth in stratified drinking water reservoir: Novel insights into algal metabolic profiling and engineering applications

Water-lifting aerator (WLA) which was developed by Professor Tinglin Huang at Xi'an University of Architecture and Technology, China has multi-functional water quality improvement that significantly inhibits the occurrence of harmful algal blooms (HABs) in deep drinking water reservoirs. However, the biological mechanism of WLA to the suppress algal growth has not been comprehensively understood. Here, the cellular mechanism that allows WLA to control HABs was explored based on the combination of both laboratory simulation and field investigation. Under simulated hydrodynamic conditions, the results showed that the cell density, chlorophyll a content, chlorophyll fluorescence parameters, and dehydrogenase activity in Microcystis aeruginosa all peaked under light conditions at 25 °C. The metabolic activity of M. aeruginosa varied significantly under low temperature at 6 °C and light conditions when cultured for 48 h. The extracellular organic matter (EOM) and intracellular organic matter (IOM) contents of M. aeruginosa were both resolved into three components. Moreover, the total fluorescence intensities from EOM and IOM both peaked under light conditions at 25 °C. The field investigation showed that the growth of algae was decreased significantly in Lijiahe drinking water reservoir with WLA application. The chlorophyll fluorescence parameters decreased significantly after vertical mixing, thereby indicating that the WLA weakened the photosynthetic ability and reduced the biological activity of algae in situ. In addition, the WLA significantly affected the vertical distribution of the phytoplankton community composition. Altogether, these results shed new lights on understanding the control of algal blooms by WLA in stratified drinking water reservoirs. WLA has broad prospect of engineering applications, which can control algal blooms of water supply resources in situ, therefore, reduce the content of disinfection by-products in drinking water treatment plants.

Phytoplankton diversity and community responses to physicochemical variables in mangrove zones of Guangzhou Province, China

The phytoplankton diversity and community response to physicochemical variables in mangrove zones of Guangdong Province along the South China coast was investigated from October to December, 2017. This study was set to investigate the phytoplankton community structure in the mangrove zone and assess the relationship between the physicochemical variables and phytoplankton species diversity. Physicochemical variables such as water temperature, total dissolve solids (tds), pH, salinity, turbidity, electrical conductivity (EC) and nutrient salts were measured in situ across the 27 stations. A total of 451 species of phytoplankton were identified belonging to 10 groups (Bacillariophta > Cyanophyta > Chlorophyta > Euglenophyta > Dinoflagellate > Eubacteria > Ochrophyta > Crytophyta > Rhodophyta > Charophyta) and quantified to constitute a standing crop of 7.11 × 10⁸ cells dm^-3. The principal component analysis (PCA) reveals that reactive nitrate, phosphate, electrical conductive (EC) and turbidity were the best abiotic factors that controlled the phytoplankton community structure in the area. However, Cannon Corresponding Analysis and Pearson correlation have explicitly revealed the impact of reactive nitrate, phosphate, EC and turbidity on the phytoplankton community structure. For instance, the CCA ordination revealed that species richness and evenness were positively influenced by reactive nitrate but negatively affected by EC, turbidity and water temperature. Diatoms were mostly controlled by total dissolved solids (tds) and salinity, whereas Euglena, cyanobacteria and green algae were impacted EC and turbidity, apart from the general contribution of the nutrient salts as delineated by CCA ordination. The Shannon diversity index value exposed different levels of organic pollution across the mangrove zone of which GD37 was the most impacted station.

Effects of fish cage culture and suspended oyster culture on macrobenthic communities in Xiangshan Bay, a semi-enclosed subtropical bay in eastern China

The impacts of fish cage culture and suspended oyster culture on macrobenthic communities were investigated in Xiangshan Bay, China, on a seasonal basis from January to October of 2015. Samples were collected from a fish cage farm, a suspended oyster farm, and two corresponding reference sites. Two-way ANOVA results showed that species richness, abundance, biomass, and Shannon-Wiener diversity differed significantly between the four different investigated areas, and different seasons as well. Cluster analysis showed that macrobenthic community composition in the fish and oyster culture areas significantly differed from that in the reference sites, respectively. Trophic structure of macrobenthos in the fish and oyster culture areas mostly clustered together owing to higher abundance and biomass of surface-deposit feeders and carnivores. The macrobenthic communities and feeding guilds correlated highly with environmental factors, such as bottom water chlorophyll a and nutrients, as well as sediment total organic carbon. Although integrated multi-trophic aquaculture is regarded as a suitable approach to coordinate desirable economic, social, and environmentally sustainable outcomes, coastal ecosystems may suffer from large-scale nutrient enrichment due to aquaculture and other human activities, which should not be considered in isolation.

Phytoplankton biomass and size structure in Xiangshan Bay, China: Current state and historical comparison under accelerated eutrophication and warming

To explore the effects of coastal eutrophication and warming on phytoplankton biomass and cell size, we analyzed current and historical data for size-fractionated chlorophyll a (chla) in Xiangshan Bay, China. Results showed that micro- and nanophytoplankton overwhelmingly dominated (>84%) in all seasons. The contribution of micro-chla was significantly lower in warm than in cold seasons, whereas contribution of pico-chla showed the opposite result. Overall, the micro-chla contribution increased with decreasing pico-chla contribution from the stable, clear, eutrophic upper bay to the turbulent, turbid lower bay, indicating that phytoplankton size structure on a spatial scale was largely shaped by water column stability and light rather than by nutrients. Since the 1980s, phytoplankton biomass, primary productivity, and micro-chla contribution in Xiangshan Bay have increased sharply with increasing nutrient amounts and temperature. Additionally, it seems that algal bloom seasonality has shifted forward from spring to winter since the power plant operations in 2006.

Assessment of microplastics derived from mariculture in Xiangshan Bay, China

Mariculture activities including enclosure, raft and cage cultures employ a variety of plastic gear such as fishing nets, buoyant material and net cages. The plastic gear poses a potential source of microplastics to the coastal environment, but relevant data on the impacts of mariculture are still limited. To this end, a semi-enclosed narrow bay (i.e., Xiangshan Bay, China) with a long-term mariculture history was investigated to assess how mariculture activities affect microplastics in seawater and sediment. The results indicated that mariculture-derived microplastics accounted for approximately 55.7% and 36.8% of the microplastics in seawater and sediment, respectively. The average microplastic abundances of seawater and sediment were 8.9 ± 4.7 (mean ± SD, n = 18) items/m³ seawater and 1739 ± 2153 (n = 18) items/kg sediment, respectively. The types of mariculture-derived microplastics included polyethylene (PE) foam, PE nets, PE film, polypropylene (PP) rope, polystyrene (PS) foam and rubber. PE foam had the highest proportion (38.6%) in the seawater samples. High usage rates and the porous structure of PE foam led to the high abundance. The average microplastic sizes of seawater and sediment are 1.54 ± 1.53 mm and 1.33 ± 1.69 mm, respectively. The spatial variations in the abundance and size of microplastics implied that the mariculture-derived microplastics in Xiangshan Bay were transported along the Bay to the open sea. The results of this study indicate that mariculture activity can be a significant source of microplastics. Further research is required to investigate how the high microplastic abundance in mariculture zone affects marine organisms, especially cultured seafood.

Responses of phytoplankton community to eutrophication in Semerak Lagoon (Malaysia)

Effects of aquaculture activities on the environmental parameters and phytoplankton community structure were investigated in a semi-enclosed lagoon located at Semerak River, Malaysia. Elevated concentrations of phosphate and ammonia were observed at the aquaculture area and the inner lagoon. Relatively low dissolved oxygen, high total chlorophyll a, and high phytoplankton abundances but low species richness were recorded. Chaetoceros, Pseudo-nitzschia brasiliana, Blixaea quinquecornis, and Skeletonema blooms were observed, and some were associated with anoxia condition. Eutrophication level assessed by UNTRIX suggests that the water quality in the lagoon is deteriorating. Dissolved inorganic phosphorus and nitrogen at the impacted area were 15 and 12 times higher than the reference sites, respectively. Such trophic status indices could provide a useful guideline for optimal aquaculture management plan to reduce the environmental impact caused by aquaculture.

Effects of the thermal discharge from an offshore power plant on plankton and macrobenthic communities in subtropical China

The ecological impact of thermal discharge has become an important issue in the field of marine and environmental protection. We focused on the effects of thermal discharge on seawater temperature and biological communities based on data from before (2006) and after (2013-2014) the construction of a power plant. The thermal discharge induced stratification, which resulted in changes in the vertical hydrodynamic conditions. Stratification combined with elevated temperatures significantly affected the phytoplankton abundance and community structure. Elevated seawater temperatures decreased the chlorophyll-a concentrations by 34% and 63%, at the surface and bottom, respectively. The elevated seawater temperature at the bottom might not be high enough to significantly affect the macrobenthos, but significantly affected the phytoplankton and zooplankton communities. Because these communities serve as food for the macrobenthic community, their changes resulted in growth of the macrobenthos. Furthermore, this effect induced macrobenthic community succession, resulting in decreased species diversity and increased dominance.

Developing an environmental water quality monitoring program for Haraz River in Northern Iran

Water quality management plans are an indispensable strategy for conservation and utilization of water resources in a sustainable manner. One common industrial use of water is aquaculture. The present study is an attempt to use statistical analyses in order to prepare an environmental water quality monitoring program for Haraz River, in Northern Iran. For this purpose, the analysis of a total number of 18 physicochemical parameters was performed at 15 stations during a 1-year sampling period. According to the results of the multivariate statistical methods, the optimal monitoring would be possible by only 3 stations and 12 parameters, including NH₃, EC, BOD, TSS, DO, PO₄, NO₃, TDS, temperature, turbidity, coliform, and discharge. In other words, newly designed network, with a total number of 36 measurements (3 stations × 12 parameters = 36 parameters), could achieve exactly the same performance as the former network, designed based on 234 measurements (13 stations × 18 parameters = 234 parameters). Based on the results of cluster, principal component, and factor analyses, the stations were divided into three groups of high pollution (HP), medium pollution (MP), and low pollution (LP). By clustering the stations, it would be possible to track the water quality of Haraz River, only by one station at each cluster, which facilitates rapid assessment of the water quality in the river basin. Emphasizing on three main axes of monitoring program, including measurement parameters, sampling frequency, and spatial pattern of sampling points, the water quality monitoring program was optimized for the river basin based on natural conditions of the study area, monitoring objectives, and required financial resources (a total annual cost of about US $2625, excluding the overhead costs).

Thermal discharge-created increasing temperatures alter the bacterioplankton composition and functional redundancy

Elevated seawater temperature has altered the coupling between coastal primary production and heterotrophic bacterioplankton respiration. This shift, in turn, could influence the feedback of ocean ecosystem to climate warming. However, little is known about how natural bacterioplankton community responds to increasing seawater temperature. To investigate warming effects on the bacterioplankton community, we collected water samples from temperature gradients (ranged from 15.0 to 18.6 °C) created by a thermal flume of a coal power plant. The results showed that increasing temperatures significantly stimulated bacterial abundance, grazing rate, and altered bacterioplankton community compositions (BCCs). The spatial distribution of bacterioplankton community followed a distance similarity decay relationship, with a turnover of 0.005. A variance partitioning analysis showed that temperature directly constrained 2.01 % variation in BCCs, while temperature-induced changes in water geochemical and grazing rate indirectly accounted for 4.03 and 12.8 % of the community variance, respectively. Furthermore, the relative abundances of 24 bacterial families were linearly increased or decreased (P < 0.05 in all cases) with increasing temperatures. Notably, the change pattern for a given bacterial family was in concert with its known functions. In addition, community functional redundancy consistently decreased along the temperature gradient. This study demonstrates that elevated temperature, combined with substrate supply and trophic interactions, dramatically alters BCCs, concomitant with decreases in functional redundancy. The responses of sensitive assemblages are temperature dependent, which could indicate temperature departures.

Role of mariculture in the loading and speciation of mercury at the coast of the East China Sea

The effects of mariculture on mercury (Hg) contamination and speciation in water, sediment and cultured fish in a typical mariculture zone located in Xiangshan bay, Zhejiang province, east China, were studied. Water, sediment and fish samples were collected from mariculture sites (MS) and from corresponding reference sites (RS) 2500 m away from the MS. The THg concentration in overlying water in Xiangshan bay reached as high as 16.6 ± 19.5 ng L^-1, indicating that anthropogenic sources in this bay may contribution on Hg contamination in overlying water. Mariculture activities resulted in an increase in THg concentration in water from surface and bottom layers, which may be attributed to the discharge of domestic sewage and the accumulation of unconsumed fish feed and fish excreta in the benthic environment. Methylmercury (MeHg) concentrations in the bottom layer of overlying water and top surface layer of porewater underneath MS were higher than at RS, implying that mariculture activities promote Hg methylation in the interface between sediments and water. In addition, the concentrations of MeHg in sediment and porewater were significantly higher in summer than winter. It was observed that THg and MeHg contents in the muscle of blackhead seabream (Acanthopagrus schlegelii) (fed by the trash fish) were significantly higher (p < 0.001) than those in red snapper (Lutjanus campechanus) or perch (Perca fluviatilis) (fed by pellet fish feed). The THg and MeHg concentrations in the fish meat were closely related to the feeding mode, which indicate that fish feed rather than environmental media is the major pathway for Hg accumulation in fish muscle.

Evidence of bacterioplankton community adaptation in response to long-term mariculture disturbance

Understanding the underlying mechanisms that shape the temporal dynamics of a microbial community has important implications for predicting the trajectory of an ecosystem’s response to anthropogenic disturbances. Here, we evaluated the seasonal dynamics of bacterioplankton community composition (BCC) following more than three decades of mariculture disturbance in Xiangshan Bay. Clear seasonal succession and site (fish farm and control site) separation of the BCC were observed, which were primarily shaped by temperature, dissolved oxygen and sampling time. However, the sensitive bacterial families consistently changed in relative abundance in response to mariculture disturbance, regardless of the season. Temporal changes in the BCC followed the time-decay for similarity relationship at both sites. Notably, mariculture disturbance significantly (P < 0.001) flattened the temporal turnover but intensified bacterial species-to-species interactions. The decrease in bacterial temporal turnover under long-term mariculture disturbance was coupled with a consistent increase in the percentage of deterministic processes that constrained bacterial assembly based on a null model analysis. The results demonstrate that the BCC is sensitive to mariculture disturbance; however, a bacterioplankton community could adapt to a long-term disturbance via attenuating temporal turnover and intensifying species-species interactions. These findings expand our current understanding of microbial assembly in response to long-term anthropogenic disturbances.