Phytoplankton Assemblage Structure Research Articles

Integrated evaluation of the impact of water diversion on water quality index and phytoplankton assemblages of eutrophic lake: A case study of Yilong Lake

Water diversion has been widely utilized to enhance lake water quality and mitigate cyanobacterial blooms. However, previous studies have mainly focused on investigating the effects of water diversion on water quality or aquatic ecological health. Consequently, there is limited research investigating the combined impact of water diversion on the water quality and the ecological health of eutrophic lakes, and whether the WQI and phytoplankton assemblages demonstrate similar patterns following water diversion. In this study, the effects of water diversion on the ecosystem health of eutrophic lakes were comprehensively evaluated based on the WQI indices and phytoplankton assemblages during the NWDP-21 and WDP-22. The results showed that the annual mean of WQI increased from 52.02 to 54.36 after water diversion, which improved the water quality of the lake, especially NH3–N and TN decreased by 58.6% and 15.2%, respectively. The phytoplankton assemblages changed significantly before and after water diversion, and we observed that the total biomass of phytoplankton decreased by 12.3% and phytoplankton diversity indices (Shannon-Wiener diversity, Pielou evenness, and Simpson index) increased by 8.6%–8.9% after water diversion, with an improvement in the connectivity and stability of the phytoplankton. Notably, enhanced adaptations of rare sub-communities for resource use in water diversion environments, and water diversion inhibited the dispersal ability of dominant functional groups, and the effects of hydrological disturbances on the structure of phytoplankton assemblage favored the ecological health of eutrophic lakes. VPA analysis further reveals that water diversion alters the drivers of phytoplankton functional group biomass and phytoplankton diversity. The results of the PLS-PM analysis clarify that water diversion indirectly impacts the total phytoplankton biomass and phytoplankton diversity primarily by modifying light availability. Significant correlations are observed between the dominant functional groups biomass and diversity indices of WQI. The trends in changes observed in water quality indices and phytoplankton following water diversion align with the evaluation of water ecological health. This study provides valuable guidance for the ecological management of the diversion project in Yilong Lake and serves as a reference for similar projects in other lakes.

Patterns and Predictors of Phytoplankton Assemblage Structure in a Coastal Lagoon: Species-Specific Analysis Needed to Disentangle Anthropogenic Pressures from Ocean Processes

Phytoplankton are dominant primary producers and key indicators in aquatic ecosystems. Understanding the controlling factors on the structure of phytoplankton assemblages is fundamental, but particularly challenging at the land–ocean interface. To identify the patterns and predictors of phytoplankton assemblage structure in the Ria Formosa coastal lagoon (south Portugal), this study combined phytoplankton abundance along a transect between the discharge point of a wastewater treatment plant and a lagoon inlet, over two years, with physico-chemical, hydrographic, and meteo-oceanographic variables. Our study identified 147 operational taxonomic units (OTUs), and planktonic diatoms (60–74%) and cryptophyceans (17–25%) dominated the phytoplankton in terms of abundance. Despite strong lagoon hydrodynamics, and the lack of spatial differences in the phytoplankton abundance and most diversity metrics, the multivariate analysis revealed differences in the assemblage structure between stations (p < 0.001) and seasons (p < 0.01). Indicator analysis identified cryptophyceans as lagoon generalists, and 11 station-specific specialist OTUs, including Kryptoperidinium foliaceum and Oscillatoriales (innermost stations) and potentially toxigenic species (Pseudo-nitzschia and Dinophysis; outer lagoon station, p < 0.05). Water temperature, pH, and nutrients emerged as the variables that best explained the changes in the phytoplankton assemblage structure (p < 0.001). Our findings provide insight into the relevance of local anthropogenic and natural forcings on the phytoplankton assemblage structure and can be used to support the management of RF and other coastal lagoons.

Long-term adjustment of phytoplankton structure to environmental traits at timescales during lifetime development and over generations

Long-term ecological research of deep Lake Mondsee covers over more than six decades of phytoplankton observation. According to our study, phytoplankton groups of various phenological traits are suitable to address the impact of two major environmental stressors: nutrient surplus by eutrophication from 1968 to 1998 and warming by climate change. Here, we focus on phytoplankton biovolume, phytoplankton assemblage structure, net changes rates, and phytoplankton biodiversity. Biweekly net change-dependent persistence of phytoplankton assemblages followed a dome-shaped relationship of observations. A short-term persistence of taxonomic traits along weeks is predominant and contributes to the structural stabilization of phytoplankton assemblages. This short-term persistence is interpreted by the benefit of lifetime adjustment of phytoplankton organisms. The long-term development phytoplankton structure is discussed as an alignment of organisms over generations. Single key taxa, as Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis &Komárek 1988, which are omnipotent players in phytoplankton assemblages and occur during different environmental scenarios in the long-term, are most suitable for long-term ecological research. Our findings interpret that phytoplankton taxa are excellent organisms to track the impact of environmental constraints due to their short generation time (1), their lifetime adjustment (2), and the re-occurrence in the long-term over generations (3).

Catchment land use drivers are weak predictors of lakes’ phytoplankton assemblage structure at functional group level

A number of studies evidenced the impact of human activities on aquatic environments worldwide. The availability of nutrients in lakes is strongly influenced by watershed land use patterns depending on the share of forestry, agriculture and urbanization level. Nearly all the previous studies, which examined the relationships between the phytoplankton community and the land use pattern on the watershed of lakes or reservoirs were performed on a taxonomic basis. In this study, 78 lakes were sampled to analyse how the different land use types affect their phytoplankton functional group compositions. Our results concluded that land use is a complex driver, and it cannot provide an unequivocally straightforward forecast, which could result in the selection of a specific functional group or taxa. Thus, land use alone is a weak predictor, but the shared effects may structure the phytoplankton assemblage composition.

Climate features or the composition of submerged vegetation? Which factor has a greater impact on the phytoplankton structure in temperate lakes?

This study compares the composition and biomass of phytoplankton assemblages of lakes with abundant vegetation dominated by (1) charophytes (Chara-lakes) and (2) angiosperms (Potamogeton-lakes). These two groups of submerged macrophytes effectively control the phytoplankton development in lakes, but differ in the feedback mechanisms involved. Despite increasing interest, the phytoplankton development in charophyte- and angiosperm-dominated lakes under different climatic circumstances remains poorly recognized. Each type of lakes was studied in two distant (>500 km apart) regions of Poland, characterized by distinctly different climate features (western – warmer, and north-eastern – cooler), with temperature differences corresponding to the predicted magnitude of the global warming-related temperature rise in the near future. Twelve lakes were selected for this study, three Chara- and three Potamogeton-lakes in each region. In addition to phytoplankton analysis, macrophytes and climatic conditions, water chemistry, and the use of land in the catchment area were studied. Although we expected that climatic differences would have greater impact on the structure of phytoplankton assemblage than that expected due to higher macrophyte biomass and lower nutrient availability in Chara- than in Potamogeton-lakes, multidimensional statistical analyses clearly distinguished between the two macrophyte types of lakes. Significantly lower values of the total phytoplankton biomass, and the biomass of diatoms and cyanobacteria occurred in Chara- vs Potamogeton-lakes. We therefore postulate that not only abundantly developed submerged macrophytes, but also the type of vegetation are important factors structuring phytoplankton development and by interacting with the physical and chemical characteristics of water show potential in mitigating the effects of climate change.

Effects of TiO2 and ZnO nanoparticles on the growth of phytoplankton assemblages in seawater

Compounds in sunscreen such as ultraviolet (UV) filters protect human skin from damage caused by UV radiation exposure. However, sunscreen components reach marine ecosystems after their release from human skin during activities such as swimming and washing, and are potentially toxic to marine organisms. TiO2 and ZnO nanoparticles (NPs) are commonly used as inorganic UV filters. In this study, we explored the effects of TiO2 and ZnO NPs on natural phytoplankton assemblages in coastal seawater. Growth rates of natural phytoplankton assemblages were significantly decreased by 10 mg L−1 TiO2 and 1 and 10 mg L−1 ZnO NP treatments. NP addition also modified the size structure of phytoplankton assemblages, and small phytoplankton (mainly cyanobacteria) are vulnerable to NPs. Because herbivore food preferences depend strongly on algal cell size, NP contamination could also affect higher trophic levels. Notably, small phytoplankton are an important component in microbial loop, and this energy transfer pathway may be more vulnerable to NP contamination.

A phytoplankton time series in the Northwestern Adriatic Sea: Structure and dynamics of the assemblages in a coastal ecosystem

Phytoplankton assemblage structure was analyzed based on time series data (2008–2019) together with environmental variables in two coastal sites in the Northwestern Adriatic Sea. The main component of phytoplankton assemblage was the diatom group. Distinct seasonal and inter annual variations in the presence of taxa were observed within the phytoplankton assemblage over the study period. Mainly four taxa showed a non-random pattern in the binary time series, such as three diatoms Skeletonema marinoi, Thalassionema nitzschioides and Dactyliosolen fragilissimus, and undetermined Dinophyceae. S. marinoi was more frequent in winter and early spring, whereas T. nitzschioides showed an opposite pattern, being more frequent in late spring and summer. In both cases, deviation from randomness was caused by a clear and almost stationary annual cycle. On the contrary, deviation from randomness depended on the long-term trend of D. fragilissimus time series, as this diatom showed an increasing frequency of occurrence since 2016. A clear phytoplankton assemblage structure affected by seasonal and environmental factors was observed. This was very evident for representative specie (i.e., S. marinoi associated with colder and rich nutrient waters or Heterocapsa niei and T. nitzschioides associated with high temperature and low nutrient conditions) and other species associated with various environmental parameters. Furthermore, the analysis of the association among phytoplankton taxa showed a partial and varied pattern. Our results highlight that phytoplankton time series showed changes in assemblage structure exhibiting a regular 12-month period affected by environmental factors. The long time series observations are important to understand the phytoplankton assemblage structure in relation to environmental changes and human pressures, crucial to achieving the Good Environmental Status in compliance to environmental directives.

Using null models and species traits to optimize phytoplankton monitoring: An application across oceans and ecosystems

Phytoplankton assemblages are privileged descriptors of the ecological status of marine ecosystems regularly included in routine monitoring programmes. The high spatial and temporal variability of phytoplankton and the intrinsic difficulties of species identifications, however, combine in making reiterate assessments of this component of marine biota particularly demanding. Coarse levels of taxonomic resolution (e.g., genus, family) or morpho-functional categories have been proposed to reduce identification efforts or to ease the analysis of phytoplankton assemblages for monitoring purposes, although with contrasting outcomes. A major issue is that, in the absence of control for the loss of information associated to these alternative approaches, their application may lead to poor representations of genuine spatial and/or temporal patterns of assemblages in relation to natural and anthropogenic sources of variation. We provided a new approach to reduce the efforts required to analyse phytoplankton assemblages that integrate morpho-functional classification of phytoplankton with the use of null models to estimate the consequent loss of information on species-level community patterns. Null models for information loss were built by randomly grouping the original species variables into a progressively decreasing number of groups, in order to identify the minimum number of aggregate variables needed to detect community patters as at species level. Aggregate variables were then defined as morpho-functional groups, by grouping species on the basis of a combination of morpho-functional traits, including general taxonomy, cell size, shape, elongation and complexity. We applied the approach to six case studies investigating the response of phytoplankton assemblages from marine and transitional water ecosystems under different environmental settings in areas spanning the world’s ocean, including coral atolls, mangroves, estuaries, coastal lagoons and inlets. The approach allowed obtaining parsimonious sets of morpho-functional groups, which were suitable to detect changes in phytoplankton assemblage structure as at species level in all case studies. Trait-based approaches to phytoplankton research and monitoring are crucial to shed light on processes underlying phytoplankton community assembly and dynamics in the face of global change. In this perspective, our framework incorporates cost-effectiveness, instances from traditional monitoring programmes aiming at the detection of community patterns, and the current need for a deeper understanding of functional responses of phytoplankton to environmental drivers.

Phytoplankton Response to Changes in Water Quality and a Flood Event in Hervey Bay, Queensland

Dynamic, integrated and complex processes dominate nearshore marine ecosystems. Industrial, agricultural and population growth delivers pollution and excess nutrient and sediment loads to nearshore marine zones. Climate change also poses serious threats to the delicate balance that exists between and within marine ecosystem processes. Methods to monitor, characterise and model nearshore marine systems have been developed to predict responses to changes in the physical, chemical and biological parameters that constitute elements of a model. Such models are useful to management authorities as they provide a tool to mitigate adverse impacts to marine ecosystems. Phytoplankton community structure provides a sensitive early warning for change to marine ecosystems. It is also a vital component of models derived to determine light attenuation and requirements for healthy seagrass and coral habitats. The multifactorial physicochemical drivers of change to marine microalgae abundance and community structure were investigated in Hervey Bay following two floods, a cyclone and destruction of 1000 km2 of seagrass. A water quality gradient from point sources to offshore sites was identified. Correlations between chlorophyll a (Chl a) and both soluble reactive phosphate (SRP) and total suspended solids was revealed. Diatoms dominated the phytoplankton community structure with seasonal and site differences detected amongst 150 phytoplankton species. Chl a, Secchi depth, SRP and pH maximised the rank correlation with phytoplankton assemblage structure (ρ = 0.63) to best ‘explain’ the link between water quality and phytoplankton (BIOENV). Indicator species include Cylindrotheca closterium for the nearshore degraded sites and Rhizosolenia sp. and Guinardia sp. (G. flaccida and G. striatula) for the offshore more pristine habitats. Following the flood in February 1995, Cylindrotheca closterium, Pseudonitzschia sp. and Skeletonema costatum bloomed at Pulgul Creek (a treated sewage effluent site), and Thalassionema frauenfeldii, Cerataulina bicornis and dinoflagellates bloomed at the mouth of the Mary River (agricultural runoff). Discharge-driven flood impact and trigger values were analysed to assist management authorities in their decision making around potential seafood biotoxin problems associated with harmful algal blooms (HAB’s). Results highlight the importance of species determination rather than Chl a assessment when evaluating the health of an ecosystem. Spring blooms of Trichodesium sp. indicate an additional nutrient source during high traffic of commercial whale watching vessels. Flood impacts highlight the need to schedule dredging, construction and other land management and development activities outside of flood periods. Commercial fishing and swimming should be avoided following a flood due to the health risks associated with toxic phytoplankton species (HAB’s) and for the health and safety of swimmers, consumers and other aquatic species. Future research to replicate this study in Hervey Bay and in other estuaries holds much value to further explore the phytoplankton species identified as bio-indicators of ecosystem health in the present study. Research yet to be published, addresses the links between water quality and seagrass epiphytes, light attenuation and the habitat requirements of seagrass in Hervey Bay.

Seasonal and interannual variation in lower Columbia River phytoplankton (2005-2018): environmental variability and a decline in large bloom-forming diatoms

Understanding the influence of biotic and abiotic factors on riverine phytoplankton dynamics is challenging, particularly as anthropogenic stressors such as eutrophication, invasive species, and climate change alter these relationships. We examined a 14 yr (January 2005 to December 2018) dataset of phytoplankton and water quality variables, along with zooplankton and nutrient concentrations, from the Columbia River (the largest river in the US Pacific Northwest) to identify seasonal and interannual patterns of phytoplankton assemblage structure and their environmental associations. Non-metric multidimensional scaling, cluster, and indicator species analyses revealed: (1) a diatom/flagellate cluster in spring/summer, associated with chlorophylla, discharge, ciliates, and Sarcodina; (2) a cyanobacteria/chlorophyte cluster in late summer/early fall, associated with higher water temperatures, increased clarity, the invasive copepodPseudodiaptomus forbesi, and veligers of the invasive Asian clamCorbicula fluminea; and (3) a mixed-taxa winter cluster of minimal abundance and biomass. Nutrients were not strongly associated with the observed structural patterns. Phytoplankton bloom duration varied interannually, between years with short springtime blooms vs. years when blooms extended across multiple months. Springtime blooms of the diatomAsterionella formosadecreased in recent years, giving way to blooms of a mixed diatom assemblage. Further, high temperature, low discharge, and more invasive zooplankton were associated with cyanobacterial blooms, suggesting that increased temperature and reduced river flows predicted due to climate change in the Pacific Northwest may lead to further impacts on the late summer/early fall Columbia River plankton community.

Assemblage Structure and Seasonality of Mesophotic Phytoplankton of Corales de Profundidad National Natural Park, Colombian Caribbean

Phytoplankton samples were taken at mesophothic depths (30–150 m) over the Frijol Bank seamount inside the Corales de Profundidad National Natural Park during the dry and rainy seasons. Sixty-four forms (genera and morpho-species) of phytoplankton were found. Seasonal influence on phytoplankton assemblage structure was detected, with a number of genera preferentially associating with the dry season. Although not statistically significant, mean cell density was higher in the rainy than in the dry season whereas mean richness was the same for practical effects. Contrasting seasonal signals on phytoplankton assemblages in other Colombian Caribbean localities in comparison with the present work are discussed.

The effects of absolute and relative nutrient concentrations (N/P) on phytoplankton in a subtropical reservoir

Abstract The elemental composition of phytoplankton is a critical factor for primary production and nutrient recycling. The increase anthropogenic nutrient input into freshwater ecosystems is affecting phytoplankton assemblage structure and its stoichiometry. Reservoirs of South China generally show low level of phosphate and it is not clear how phytoplankton can grow and occasionally bloom in such conditions. Therefore, an indoor experiment was conducted to investigate the response of natural phytoplankton communities to 25 levels of supplied nitrogen to phosphorus ratios (N/P), arising from the combination of 5 levels of N and P. Our aim was to check the effects of absolute and relative N and P on phytoplankton growth and structure. We assumed that Alkaline Phosphatase (APA) provides a way to use alternative P resource. Our hypotheses include: (1) phytoplankton stoichiometry would be in homeostasis (sensu Sterner & Elser, 2002) under different N and P treatments; (2) absolute nutrient values rather than its ratio matters for phytoplankton assemblage; and (3) phytoplankton cell size declines to lower P requirements facing P limitation. Results showed that phytoplankton in this subtropical reservoir use alternative P sources via APA to support its growth. The absolute values of N and P instead and not their ratios were important for phytoplankton. The N/P ratio cannot be a reliable indicator for nutrient limitation or phytoplankton shift. During the fast-growing phase, their elemental contents were not sensitive to supplied nutrients, and their stoichiometry was more constrained compared to that in slow-growing phase. The plasticity of cellular stoichiometry was mainly due to the variations of cellular P. Phytoplankton stoichiometry was weakly homeostatic, and this mechanism provides a strategy to keep growth relatively stable in a variable nutrient environment.

Environmental factors controlling the dynamics of phytoplankton communities during spring and fall seasons in the southern Sunda Shelf.

Phytoplankton play important roles in marine ecosystems and have major impacts on the global biogeochemical cycles, yet the knowledge of the processes for oceanic environments controlling the phytoplankton dynamics still needs to be improved, particularly in the coastal ecosystems. Monitoring diversity of phytoplankton communities, including micro/nano- and pico-forms, as well as their dynamics in relation to environmental factors, is thus of critical significance. Here, we conducted two cruises in the southern Sunda Shelf during spring and fall 2016 to investigate the community structure and dynamics of phytoplankton assemblages in relation to environmental factors combining microscopy and flow cytometry. Micro/nanophytoplankton communities changed from Trichodesmium spp. and diatoms co-dominance in spring to communities dominated by Trichodesmium spp. in fall. Diatoms were a highly diverse group, with 78 species, followed by dinoflagellates (35 species). Differences in average abundance of micro/nanophytoplankton between spring and fall might be attributed to the shift in dominance of Trichodesmium spp. and diatoms. Picophytoplankton characterized by a great abundance of picocyanobacteria were dominated by Synechococcus. The dynamics of picophytoplankton during spring and fall might be associated with the differences in dominant Synechococcus strains. Environmental variables had significant influence on the dynamics of phytoplankton communities, especially nitrate and silicate. Silicate was a major driver responsible for the variations of micro/nanophytoplankton. Low silicate potentially limited the diatom growth during fall, leading to the overwhelming dominance of Trichodesmium spp. Picophytoplankton showed positive correlations with nitrate and silicate, suggesting that these nutrients collectively controlled variations in picophytoplankton communities during spring and fall.

The Importance of Allelopathic Picocyanobacterium Synechococcus sp. on the Abundance, Biomass Formation, and Structure of Phytoplankton Assemblages in Three Freshwater Lakes.

The contribution of picocyanobacteria to summer phytoplankton blooms, accompanied by an ecological crisis, is a new phenomenon in Europe. This issue requires careful investigation. We studied allelopathic activity of freshwater picocyanobacterium Synechococcus sp. on phytoplankton assemblages from three freshwater lakes. In this study, the allelopathic activity of the Synechococcus sp. on the total abundance, biomass, as well as structure of the phytoplankton assemblages were investigated. Our results indicated that addition of exudates obtained from Synechococcus sp. affected the number of cells and biomass of the phytoplankton communities; the degree of inhibition or stimulation was different for each species, causing a change in the phytoplankton abundance and dominance during the experiment. We observed that some group of organisms (especially cyanobacteria from the genus Aphanothece, Limnothrix, Microcystis, and Synechococcus) showed tolerance for allelopathic compounds produced and released by Synechococcus sp. It is also worth noting that in some samples, Bacillariophyceae (e.g., Amphora pediculus, Navicula pygmaea, and Nitzschia paleacea) were completely eliminated in the experimental treatments, while present in the controls. This work demonstrated that the allelopathic activity exhibited by the Synechococcus sp. is probably one of the major competitive strategies affecting some of the coexisting phytoplankton species in freshwater ecosystems. To our best knowledge this is the first report of the allelopathic activity of Synechococcus sp. in the freshwater reservoirs, and one of the few published works showing allelopathic properties of freshwater picocyanobacteria on coexisting phytoplankton species.

Structure and environmental drivers of phytoplanktonic resting stage assemblages in the central Mediterranean Sea

Phytoplankton species can produce resting stages that persist in the sediment over long periods and accomplish important ecological functions. With the aim of investigating the phytoplankton assemblage structure in relation to environmental drivers and human pressures, we analyzed resting stages of diatoms and dinoflagellates, including harmful algal bloom taxa, in the surface sediments of 3 Mediterranean regional areas. Abundance of resting stages was determined by molecular quantitative polymerase chain reaction assay. Multivariate data analysis confirmed that the abundance of resting-stage assemblages seemed related to depth. Regional differences in the composition of the resting-stage assemblages were evident and environmental drivers were correlated with those regional differences. Three main groups of samples were defined according to SST and depth thresholds. Samples from the northern and central Adriatic Sea (average SST < 18°C) formed the richest assemblages, both in terms of abundance and species richness, while deep samples from all other basins (depth > 368 m) were poorer and less diverse than those from shallower sites (depth ≤ 368 m). Resting-stage taxa contributed differently to the 3 groups. Diatom spores and dinoflagellate cysts were the most abundant taxa, but Alexandrium minutum cysts and Ditylum brightwellii spores also accounted for a large share of the overall inter-group compositional distance. The structure of resting-stage assemblages can be regarded as a time- and space-integrated response of a subset of phytoplankton species to environmental conditions, including the physical oceanographic dynamics that favor or prevent sedimentation of resting stages.

Life in suspension and its impact on phytoplankton morphology: an homage to Colin S. Reynolds

The amazing morphological diversity of phytoplankton has to be considered an evolutionarily driven compendium of strategies to cope with the strong variability and unpredictability of the pelagic environment. Phytoplankton collects unicellular and colonial photosynthetic organisms adapted to live in apparent suspension in turbulent water masses. Turbulence represents a key driver of phytoplankton dynamics in all aquatic ecosystems and phytoplankton morphological variability is the evolutionary response of this group of photosynthetic organisms to the temporal and spatial scales of variability of turbulence. This paper reviews the existing literature on the effects exerted by turbulence on phytoplankton populations and is aimed at showing how deeply turbulence contributes to the shape and size structure of phytoplankton assemblages. Our aim is to explore how turbulence governs phytoplankton access to resources and, at the same time, how the shape and size structure of phytoplankton represent the evolutionary way in which this group of organisms has optimised its survival in the highly dynamic aquatic environment. The paper is intended to serve as an homage to the (phytoplankton) ecologist Colin S. Reynolds. His life-long work highlighted how profoundly the ecology of phytoplankton depends on the physical constraints governing the movements of the water masses in which phytoplankton evolved and lives.

The Influence of Environmental Factors on Phytoplankton Varietya Case Study of Three Ponds of Western Poland

Abstract The structure of phytoplankton assemblages in three small water bodies was compared and abiotic factors were described. It indicated considerable differences in the species abundance and biomass of the phytoplankton as well as the chemical composition of water between artificial pond (No. 2) and others. A total of 455 phytoplankton taxa were recorded. All ponds were characterized by greatest species richness of Chlorophyta. The highest biomass was noted in August-September 2015, and it was true for each pond. The CCA models showed dependences between the variables under study and phytoplankton groups. They indicated which environmental variables had the greatest influence on the biomass of phytoplankton in the waterbodies under analysis. The biomass of most of the taxonomic group in the phytoplankton (except Miozoa) depended on the presence of nitrogen not only in form of nitrates but also in the form of mineral nitrogen. The research findings suggest the trend of future studies on the phytoplankton in these ponds. The analysis of its variability should also include the influence of light and the influence of consumers on the food chain in the ecosystem.

Comparison of Two Methods to Assess the Size Structure of Phytoplankton Community Assemblages, in Liaodong Bay, China

Liaodong Bay is one of the largest semi-enclosed bays located in Bohai Sea, in northeast China. It is an important feeding and spawning place, even wintering and breeding migration base for many marine organisms. The size structure of phytoplankton communities is a key feature of marine ecosystems and can be used as an indicator for algae disaster, but the methods to evalute is still challenging. Here, we compared the size-fractionated chlorophyll-a method with a high-throughout sequencing method in an evaluation of the size structure of phytoplankton assemblages in Liaodong Bay, China, in 2014. The proportion of picophytoplankton was estimated at just 19% according to the results based on size-fractionated chlorophyll-a, which likely represents a severe underestimation. The sequencing method confirmed that many kinds of phytoplankton species appeared in more than one size-fractionated filter membrane, with some even dominating where the filter membrane pore size was greater than the individual phytoplankton size. According to the sequencing method, the phytoplankton assemblages in Liaodong Bay were dominated by picophytoplankton (average proportion = 44%), followed by the nanophytoplankton (average 32%), a composition that is more consistent with other studies. The sequencing method provides a more robust way to assess the size structure and taxonomic diversity of marine phytoplankton communities.

A single pulse of diffuse contaminants alters the size distribution of natural phytoplankton communities

The presence of a multitude of bioactive organic pollutants collectively classified as pharmaceuticals and personal care products (PPCPs) in freshwaters is of concern, considering that ecological assessments of their potential impacts on natural systems are still scarce. In this field experiment we tested whether a single pulse exposure to a mixture of 12 pharmaceuticals and personal care products, which are commonly found in European inland waters, can influence the size distributions of natural lake phytoplankton communities. Size is one of the most influential determinants of community structure and functioning, particularly in planktonic communities and food webs. Using an in-situ microcosm approach, phytoplankton communities in two lakes with different nutrient levels (mesotrophic and eutrophic) were exposed to a concentration gradient of the PPCPs mixture at five levels. We tested whether sub-lethal PPCPs doses affect the scaling of organisms' abundances with their size, and the slope of these size spectra, which describe changes in the abundances of small relative to large phytoplankton. Our results showed that a large proportion (approximately 80%) of the dataset followed a power-law distribution, thus suggesting evidence of scale invariance of abundances, as expected in steady state ecosystems. PPCPs were however found to induce significant changes in the size spectra and community structure of natural phytoplankton assemblages. The two highest treatment levels of PPCPs were associated with decreased abundance of the most dominant size class (nano-phytoplankton: 2–5 μm), leading to a flattening of the size spectra slope. These results suggest that a pulse exposure to PPCPs induce changes that potentially lead to unsteady ecosystem states and cascading effects in the aquatic food webs, by favoring larger non-edible algae at the expense of small edible species. We propose higher susceptibility due to higher surface to volume ratio in small species as the likely cause of these structural changes.

Lidar Monitoring of Chlorophyll a During the XXIX and XXXI Italian Antarctic Expeditions

Although it is known that the Ross Sea is responsible for more than a quarter of CO2 absorption of the Southern Ocean, more information is needed to model the primary production of this key area. In particular, it is necessary to improve the characterization of the size class distribution, biomass and taxonomic composition of phytoplankton in the Ross Sea. Recently, an innovative compact lidar fluorosensor was deployed for real-time sensing of chlorophyll a, during the Ross Sea Mesoscale Experiment (RoME), conducted in the XXIX (2014) and XXXI (2016) Italian Antarctic expeditions. Furthermore, high-performance liquid chromatography (HPLC) was also performed to provide pigment analysis of in situ samples. Lidar fluorosensors are laser-induced fluorescence (LIF) instruments and have been extensively operated by the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) since the 1990s to monitor water bodies. Spectra obtained with LIF contain signatures of phytoplankton pigments, chromophoric dissolved organic matter and dispersed impurities, such as crude oils. The study of algal pigments provides not only the phytoplankton biomass—directly linked to chlorophyll a—but also its taxonomic composition through detection of several accessory pigments. Moreover, some models allow the identification of phytoplankton size classes. Lidar and HPLC mapped the spatiotemporal distribution of algal biomass and showed that during RoME, the phytoplankton assemblage structure was dominated by large-size cells (micro-phytoplankton) and the prevailing algal groups were diatoms.