High Phytoplankton Diversity Research Articles

Maintenance of High Phytoplankton Diversity in the Danubian Floodplain Lake over the Past Half-Century.

Riverine floodplains are recognized as centers of biodiversity, but due to intense anthropogenic pressures, many active floodplains have disappeared during the last century. This research focuses on the long-term changes in phytoplankton diversity in the floodplain lake situated in the Kopački Rit (Croatia), one of the largest conserved floodplains in the Middle Danube. The recent dataset from 2003 to 2016 and historical data from the 1970s and 1980s indicate high phytoplankton diversity, summarising 680 taxa for nearly half a century. The variability of species richness is driven by specific in-lake variables, particularly water temperature, water depth, total nitrogen, pH, and transparency, determined by a redundancy analysis of the current data. The high phytoplankton diversity levels are sustained regardless of intense pressures on the lake environment, including exposure to strong anthropogenic pollution in the past and extreme hydrological events, both droughts and floods, which have increasingly affected this part of the Danube in the last decades. The conserved hydrological connection between various biotopes along the river-floodplain gradient seems crucial in maintaining high phytoplankton diversity. Accordingly, conserving natural flooding is mandatory to maintain high biodiversity in complex and dynamic river-floodplain systems.

Drivers and mechanisms of harmful algal blooms across hydrologic extremes in hypereutrophic grand lake st marys (Ohio)

Grand Lake St. Marys (GLSM) is a large, shallow, hypereutrophic lake situated in an agricultural watershed with high-nutrient, non-point source runoff. The resulting harmful algal blooms (HABs) are typically dominated by Planktothrix, which can produce microcystin, a potent cyanobacterial toxin that has varied in concentration over the past decade. Some drivers of bloom biomass and toxicity in GLSM are described, but recent years (2019–2022) have exhibited anomalous combinations of winter ice cover and spring runoff, suggesting that additional factors contribute to variability in HAB severity and toxicity. 2020 and 2022 were typical water years, with normal tributary runoff volumes occurring primarily in late winter and spring after either little to no ice cover (2019–2020) or heavy/prolonged ice cover (2021–2022). However, 2021 exhibited prolonged winter ice and low winter/spring runoff. 2020 and 2022 were typical bloom years, with near monoculture, Planktothrix-dominated biomass (11 to 405 μg/L total chlorophyll) and high total concentrations of microcystins (<0.3 to 65 μg/L). However, the first half of 2021 exhibited lower biomass (18 to 65 μg/L chlorophyll a) and toxin concentrations (0.4 to 2.0 μg/L). While biomass returned to bloom levels when external tributary loading increased, ammonium uptake and regeneration rates and microcystin concentrations remained low throughout 2021 (in contrast to other years). Overall, potential ammonium uptake rates strongly correlated with chlorophyll and microcystin concentrations (Bayesian R2 = 0.59; 95% CI = 0.44 to 0.65). Phytoplankton diversity was higher in 2021 than other years, especially in spring/early summer, with increased dinoflagellates and diatoms in spring, followed by a mixed cyanobacterial assemblage in summer. These results suggest that lower external nutrient loads can drive immediate positive impacts on water quality, such as reduced HAB biomass and toxicity and higher phytoplankton diversity, even in hypereutrophic, shallow lakes.

Insight into diversity change, variability and co-occurrence patterns of phytoplankton assemblage in headwater streams: a study of the Xijiang River basin, South China.

Phytoplankton has been used as a paradigm for studies of coexistence of species since the publication of the "paradox of the plankton." Although there are a wealth of studies about phytoplankton assemblages of lakes, reservoirs and rivers, our knowledge about phytoplankton biodiversity and its underlying mechanisms in mountain headwater stream ecosystems is limited, especially across regional scales with broad environmental gradients. In this study, we collected 144 phytoplankton samples from the Xijiang headwater streams of the Pearl River across low altitude (< 1,000 m) located in Guangxi province, intermediate altitude (1,000 m < altitude <2,000 m) in Guizhou province and high altitude (> 2,000 m) in Yunnan province of China. Our study revealed high phytoplankton diversity in these streams. Freshwater phytoplankton, including cyanobacteria, Bacillariophyta, Chlorophyta, Rhodophyta, Chrysophyta, Euglenophyta, Glaucophyta, Phaeophyta and Cryptophyta, were all detected. However, phytoplankton alpha diversity exhibited a monotonic decreasing relationship with increasing altitude. High altitudes amplified the "isolated island" effect of headwater streams on phytoplankton assemblages, which were characterized by lower homogeneous selection and higher dispersal limitation. Variability and network vulnerability of phytoplankton assemblages increased with increasing altitudes. Our findings demonstrated diversity, variability and co-occurrence patterns of phytoplankton assemblages linked to environmental factors co-varying with altitude across regional scales.

High phytoplankton diversity in eutrophic states impedes lake recovery

AbstractAimThe widely observed positive response of productivity to biodiversity, known as the biodiversity‐productivity relationship (BPR), underpins nature‐based solutions for mitigating and adapting to global changes. Little is known of the role of such emergent processes in the restoration of damaged ecosystems. Here, we test for evidence of a BPR in degraded freshwater lakes, and its role in underpinning or undermining lake recovery from eutrophic states.LocationLower Yangtze and Huaihe river basins, China, East Asia.TaxaFreshwater phytoplankton; also macrophytes, fish, zooplankton and zoobenthos.MethodsA systematic review of biodiversity studies was conducted to enumerate freshwater biodiversity change during eutrophication, encompassing 572 samples from 155 lakes in East China. Empirical samples were then taken of 93 phytoplankton communities from 38 lakes in ecologically degraded states of eutrophication. Samples were analysed for niche overlap in relation to biodiversity and productivity, and metrics of network structure indicative of community stability.ResultsReviewed publications on eutrophication in East China lakes revealed losses in biodiversity of macrophytes, fishes, zooplankton and zoobenthos but not phytoplankton. Empirically sampled eutrophic lakes maintained high phytoplankton biodiversity through niche differentiation, and phytoplankton biodiversity correlated positively with biomass, in line with the expectations of BPR.ConclusionsThe positive effect of biodiversity on phytoplankton productivity in eutrophic lakes acts in opposition to the negative impacts on productivity induced by eutrophication‐management strategies of nutrient suppression. In degraded systems, the BPR contributes to sustaining productivity of lake phytoplankton communities, impeding recovery from a eutrophic state. This is a case of the BPR playing an undesirable role at the ecosystem level. Lake recovery programmes need to anticipate that the control of phytoplankton biomass will depend on reducing nutrients to a level sufficient to degrade the internal structure of the phytoplankton community.

Composition and spatial-temporal dynamics of phytoplankton community shaped by environmental selection and interactions in the Jiaozhou Bay

The Jiaozhou Bay as a model marine ecosystem in China has been intensively investigated over the last 90 years. However, detailed phytoplankton community composition, spatial-temporal dynamics, and its assembly mechanism were still unclear. To address these, we systematically examined the composition and spatial-temporal dynamics of phytoplankton in the Jiaozhou Bay through high-throughput sequencing of 18S rDNA V4. Analysis of 468 samples from 12 sampling sites over one full year revealed much higher phytoplankton diversity than previous reports, and strong seasonal succession patterns. Some phytoplankton also showed spatial variations, although the phytoplankton community didn't show significant distance-decay pattern. Environmental factors (especially temperature), species-species interrelationships and unique resting stages were uncovered to be the main contributors instead of stochastic process in shaping the phytoplankton community assembly. The overwhelming positive correlations between phytoplankton and other protists suggested that coevolution might be critical in this marine ecosystem. Complementary distributions of different amplicon sequence variants (ASVs) of same genera, such as Skeletonema marinoi (ASV_2) and Skeletonema tropicum (ASV_263) of the genus Skeletonema, suggested that phytoplankton have evolved differentially to exploit a wide range of ecological niches. This study laid a solid foundation for asertaining phytoplankton composition and spatial-temporal dynamics in temperate seawaters and mechanisms underlying phytoplankton community assembly, allowing in-depth studies of marine ecology.

The Diversity of Phytoplankton in a Combined Rice-Shrimp Farming System in the Coastal Area of the Vietnamese Mekong Delta

An assessment of varying density, species composition and dynamics of phytoplankton in a combined rice-shrimp culture was carried out in My Xuyen district, Soc Trang province in the Vietnamese Mekong delta. Water was sampled six times at six separate locations within the culture system, on days 1, 20, 34, 57, 68, and day 81 of the rice-shrimp crop cycle. The results showed the abundance of 95 phytoplankton species belonging to five phyla including Cyanophyta, Chlorophyta, Bacillariophyta, Euglenophyta, and Pyrrophyta. The values of Shannon–Wiener index indicated high phytoplankton diversity, while the water quality ranged from medium to good. A Cluster Analysis showed that the phytoplankton density variation can be divided into three distinct periods. The initial phase of crop growth was dominated by Pandorina morum, Pediastrum simplex, Eudorina elegans, Oscillatoria limosa, and Anabaena circinalis. The midstage, reproductive phase of crop growth was dominated by Scenedesnus acuminatus, Pediastrum duplex, Closterinm setaceum, Scenedesnus quadricauda, and Actinastnum hantzschii. Whereas Scenedesnus acuminatus, Scenedesnus quadricauda, Closterinm closterioides, Staurastrum arcuatum, Euglena nhrenbergii, and Phacus lnsmorensis were dominant at the end of crop cycle. The findings provide useful information on phytoplankton assemblages in a typical rice-shrimp culture, which has recently gained popularity as an adaptive livelihood system.

Relationship between phytoplankton community and water parameters in planted fringing mangrove area in South China

Reforestation has been commonly adopted to increase the mangrove areas lost due to developments. A diverse phytoplankton community is critical to mangrove ecosystem functions; however, its compositions in planted mangrove habitats have seldom been reported. The present study, based on the temporal and spatial variations of phytoplankton community and water parameters, evaluated their relationships in a 20-year old artificially planted fringing mangrove in South China. Thirty-one phytoplankton taxa were identified from tidal water collected from three sites along a planted mangrove shoreline: within, and at the edge of mangroves, and at bare shoreline without mangroves. In all three sites, Bacillariophyta (diatom) was the most abundant phylum, dominated by Navicula and Nitzschia at 9.82–83.76% and 2.57–33.97%, respectively. The overall diversity ranged between 0.41 and 1.94. The temporal variations of phytoplankton and water parameters were more obvious than site differences. Higher phytoplankton diversity was found in summer, with increased green algae and cyanobacteria abundance accompanied by riverine discharge. There was site-specific dominance in some phyla between June and January, noticeably Chlorophyta, Cyanophyta, Dinophyta, and Euglenophyta. A potential toxic dinoflagellate Peridinium sp. was identified during fall and winter, serving as a warning to probable harmful bloom events. Multivariate statistical analyses revealed the abundance of major phytoplankton taxa significantly related to water physiochemical parameters, especially nitrate, ammonium, total phosphorous and orthophosphate. The present study suggests that mangrove vegetation may influence water quality and shape phytoplankton composition, but temporal differences were more significant. Compared with the protected natural mangroves in the National Nature Reserve nearby, this planted fringing mangrove habitat not only had lower nutrients, especially total nitrogen in tidal water, but also had different dominant phytoplankton species and lower species richness. The 20-year old artificially planted mangroves may still not serve the same ecological function as the protected natural mangrove forest.

Application of multiple indices to the evaluation of trophic and ecological status in a tropical macrotidal estuary (Equatorial Margin, Brazil)

ABSTRACT The Paciência river estuary (PRE) is an Amazonian estuary with relevant socio-economic importance; however, it is undergoing a continuous anthropogenic pressure such as the input of untreated domestic effluents. Hence, the phytoplankton community and trophic indices were analysed during three seasons in 2017 to assess the water quality and understand the degree of human influence in a macrotidal estuary. The trophic state of the PRE was determined by applying the trophic state index (TSI), trophic index, and Karydis trophic index, and ecological status by diversity metrics (diversity, evenness, richness, and dominance). Multivariate analysis indicated that TSI and dominance index were the most sensitive indices to changes in environmental conditions. The precipitation regime characterised the estuary in two different trophic scenarios. PRE was hypereutrophic in the dry season and mesotrophic in the rainy/transitional seasons based on the TSI. A high dominance index was recorded in the dry season with blooms of Thalassiosira rotula, reflecting an ecological disturbance. A higher phytoplankton diversity was recorded in the rainy/transitional seasons, indicating a tendency toward a lower stressed ecosystem. Therefore, understanding the trophic state variability in tropical estuaries and its response to changes in phytoplankton ecology is essential to support the management of coastal ecosystems.

Patterns of phytoplankton community structure and diversity in aquaculture ponds, Henan, China

In aquaculture, phytoplankton contribute to primary productivity, helping maintain fishery harvests and water stabilization. To better understand the drivers controlling phytoplankton communities, sampling was conducted during two seasons in 185 aquaculture ponds that cultured five species of aquatic animals (channel catfish, common carp, grass carp, crayfish and largemouth bass). Principal coordinate analysis (PCoA), redundancy analysis (RDA), and generalized linear model (GLM) were applied to quantify the relative importance of multiple factors to phytoplankton species composition and diversity. The PCoA results demonstrated that in spring, phytoplankton species composition showed no distinct differences among the 5 cultivated-animal ponds. In summer, phytoplankton species composition had a distinct pattern, which was clustered into three distinct groups. The RDA results revealed that the variation in the phytoplankton composition was closely correlated with the water temperature, conductivity, dissolved organic carbon (DOC), alkalinity, and nitrate in spring. In summer, different variables, including cultivated animals, alkalinity, pH and dissolved oxygen (DO), were responsible for explaining species composition patterns. In spring, no significant difference in phytoplankton α-diversity was found among the 5 cultivated-animal ponds. In summer, significantly higher α-diversity was found in the channel catfish and crayfish ponds than in the other ponds. GLM analysis showed that phytoplankton density, cultivated animals, and conductivity can be used to explain phytoplankton diversity. Although no effect of cultivated animals was found during the early aquaculture stage, the results from the summer samples demonstrated that cultivated animals have an important influence on phytoplankton communities. Therefore, we suggest that in intensive fish-stocking ecosystems, top-down effect is an important strength on phytoplankton communities. In terms of preventing algal blooms, a low density of phytoplankton is important for maintaining high phytoplankton diversity and water stabilization in aquaculture. Our results can provide useful information for water management practices in aquaculture ponds.

Beyond nitrogen: phosphorus – estimating the minimum niche dimensionality for resource competition between phytoplankton

The niche dimensionality required for coexistence is often discussed in terms of the number of limiting resources. N and P limitation are benchmarks for studying phytoplankton interactions. However, it is generally agreed that limitation by small numbers of resources cannot explain the high phytoplankton diversity observed in nature. Here, we parameterised resource competition models using experimental data for six phytoplankton species grown in monoculture with nine potential limiting resources. We tested predicted species biomass from these models against observations in two-species experimental mixtures. Uptake rates were similar across species, following the classic Redfield ratio. Model accuracy levelled out at around three to five resources suggesting the minimum dimensionality of this system. The models included the resources Fe, Mg, Na and S. Models including only N and P always performed poorly. These results suggest that high-dimensional information about resource limitation despite stoichiometric constraints may be needed to accurately predict community assembly.

Assessing the phytoplankton community and diversity in relation to physico-chemical parameters in a tropical reservoir of the River Ganga basin, India

Phytoplankton species composition and diversity and its relation to physico-chemical parameters were studied in Jargo Reservoir located on River Jargo, a tributary of River Ganga basin, India. A total of 137 phytoplankton species belonging to 8 divisions were recorded indicating rich phytoplankton diversity in the North Indian reservoir. Bacillariophyta contributed the highest number of species followed by Chlorophyta. Filamentous algae such as Geitlerinema sp., Pseudoanabaena sp., Oscillatoria sp. and Phormidium sp. were highly abundant. The contribution of the top ten species ranged between 63% and 98% of total phytoplankton density. PCA analysis of physico-chemical revealed six principal components (HCO3, TDS, BOD, DOM, air temperature and pH) which significantly affected the succession of phytoplankton in Jargo Reservoir. The CCA analysis of phytoplankton species and physico-chemical parameters revealed that Ochrophyta and Miozoa were highly influenced by high CO2 and PO4. Higher phytoplankton diversity and species richness were observed during the late winter season and rainy season, respectively. Our investigation recommends that fish production in the reservoir could be enhanced by stocking with fingerlings of silver carp, which has the potential to utilise the unconsumed population of abundant Myxophyta.

Comparative Study on Phytoplankton Community in Two Newly Dug Ponds in Institut Teknologi Sumatera

Phytoplankton community plays an important ecological role in the aquatic ecosystems as the primary producers and forms the fundament of the aquatic food chain for supporting the water community. Thus, the phytoplankton community structure is a good indicator of water quality due to its sensitiveness to environmental stresses. Two newly dug ponds in Institut Teknologi Sumatera may give an opportunity to study the early colonizing stages of various freshwater communities including phytoplankton. The study attempted to determine the composition and abundance of phytoplankton. Samples were collected from two ponds (A and C) in the reservoir water of Institut Teknologi Sumatera. The content of Phosphorus (P), Nitrogen (N), and Chlorophyll-a (algae biomass) were determined. Phytoplankton had higher diversity in Pond C than Pond A in the study period, in which a total of seven taxa were found, namely Bacillariophycea, Cyanophyceae, Chlorophyceae, Conjugatophyceae, Dinophyceae, Euglenophyceae, Gymnodiniaceae. The most species abundance of both ponds was Peridinium sp. and Trachelomonas sp. The Pond C had the highest mean value of the Shannon-Wiener diversity index. The Linear mixed-effect model showed that low turbidity will result in high phytoplankton diversity. The finding of this study suggests that higher phytoplankton diversity would achieve a natural carrying capacity, and thus would serves as an indicator of ecosystem health.

Impact of monsoon-induced discharge on phytoplankton community structure in the tropical Indian estuaries

To understand the influence of monsoon-induced river discharge and associated environmental changes on phytoplankton community structure in the Indian estuaries, physical and biogeochemical parameters were collected from 28 major and medium estuaries along the Indian coast during the peak discharge period. Relatively higher river discharge was recorded in the estuaries located in northern India associated with higher suspended particulate matter (SPM), which arrested light penetration, resulting in a decreased in phytoplankton abundance and biomass. In contrast, higher phytoplankton abundance and biomass were observed in the estuaries located in southern India due to lower discharge and SPM than northern India. Diatoms were the dominant phytoplankton group in the Indian estuaries, except in estuaries located in the southeast coast, where blue–green algae predominate due to the existence of brackish water and stagnant water conditions due to less discharge. Higher phytoplankton diversity was observed in the south Indian estuaries than north Indian estuaries due to the long water residence time in the former. A present study is revealing that the magnitude of river discharge and SPM load seems to be the primary factors controlling phytoplankton abundances and community composition in the Indian estuaries.

Phytoplankton diversity and trophic status of Lake Maninjau, West Sumatra, Indonesia

Abstract. Sulastri, Henny C, Nomosatryo S. 2019. Phytoplankton diversity and trophic status of Lake Maninjau, West Sumatra, Indonesia. Pros Sem Nas Masy Biodiv Indon 5: 242-250. Microcystis blooms have been recorded in Lake Maninjau in 2000, October 2011 and recently on April 2018. Microcystis bloom was characterized by green color enhancement in the column water due to high concentration of chlorophyll-a reach to > 100 µg.L-1. The occurrence of phytoplankton bloom in this lake was not recorded all the year but Microcystis was disappeared and the water is clear again in a certain period. This study was aimed to reveal phytoplankton diversity and relation to trophic status in Lake Maninjau. Phytoplankton diversity and water quality include water transparency, temperature, DO, pH, conductivity, and nutrient were observed in 2009, 2014, 2015, 2016 dan 2018. Phytoplankton sample and water quality parameters were measured in the euphotic zone at nine stations. Three variable chlorophyll-a, Secchi depth (transparency) and total phosphorus concentration used to calculate the trophic state index. There are 121 species of phytoplankton belong to phylum Chlorophyta (74 species), Cyanophyta (23 species), Pyrrhophyta (7 species) dan Euglenophyta (4 species). The trophic status in Lake Maninjau showed variability temporally; it was mesotrophic, meso-eutrophic, eutrophic and hiper-eutrophic. Hypereutrophic status was characterized by low phytoplankton diversity (27 species), high chlorophyll-a, nutrient concentration, and Microcystis aeruginosa abundance (4180.932 x 103 individual.L-1). Mesotrophic was characterized by high phytoplankton diversity (63 species) belong to phylum Chlorophyta especially family Desmidiaceae, Oocyataceae, Scenedesmusceae, and low nutrient concentration. The higher trophic status is more decrease phytoplankton diversity.

The variability in the hydrosedimentological regime supports high phytoplankton diversity in floodplain: a 12-year survey of the Upper Paraná River

&lt;p&gt;The alpha, beta, and gamma diversity are important tools for conservation studies, and the distribution of species in space and time is essential to provided insights regarding diversity patterns and processes that modify the ecosystem and the community responses to such changes. Thus, a long-term ecological date was used to evaluate in 12 biotopes the phytoplankton composition and diversity within selected habitats (alpha diversity), between habitats (beta diversity) and across the upper Paraná River floodplain (gamma diversity). We evaluate the environmental variability of the hydrosedimentological cycles (limnophase and potamophase) during 12 years, associated with the water level variability and with the environmental heterogeneity as drivers of the phytoplankton composition and diversity in the upper Paraná River floodplain. Remarkable gamma diversity was recorded especially in limnophase, however, years with intense flood presented high gamma diversity, and years with extreme drought presented low gamma diversity, although without significant differences. The alpha diversity was significantly different on spatial and temporal scales. The beta diversity showed high values, however with low temporal variability and without correlation with the hydrosedimentological regime of the Paraná River. Overall, these results indicate that the variability in the hydrosedimentological regime associated with the periodicity, duration, and amplitude of limnophase and potamophase, and the pattern of mosaic of habitats in this floodplain are essential for sustaining much of the diversity phytoplankton diversity and ecosystem integrity, and that this approach is relevant and proved be useful to understand floodplain systems and associated phytoplankton community.&lt;/p&gt;

Phytoplankton composition and water chemistry of a tidal creek (Ipa-Itako) part of Lagos Lagoon

The composition and diversity of planktonic algae in a sluggish tidal freshwater/brackish mangrove dominated creek (Ipa Itako) part of the Lagos lagoon was investigated for twelve months (February 2010 - January 2011). The surface water pH varied between 6.5 (December 2010) and 8.6 (August 2010) indicating a slightly acidic to alkaline nature of the creek. The salinity was higher during the dry months (November- April) and phosphate - phosphorus and nitrate-nitrogen recorded highest values (3.50 and 16.70 mg/L) respectively in June, 2010. Ninety three species belonging to forty nine genera from five classes (Bacillariophyceae, Chlorophyceae, Euglenophyceae, Cyanophyceae and Xanthophyceae) were recorded. Bacillariophyceae constituted the most abundant group making up 72.85% of cells/ml followed by the Chlorophytes (18.02%) then the blue green (7.65%), euglenoids (1.40%) and xanthophytes (0.07%) with only Vaucheria sp. recorded as a representative of the group. Higher phytoplankton diversity and cell counts were recorded in the dry months than in the wet months. Navicula, Pinnularia, Cymbella (Diatoms) and Closterium (Chlorophyceae) were more frequently occurring species. Community structure analysis indices used indicated a diverse but stressed environment. Key words: Diversity, phytoplankton, creek, eutrophication.

Density‐Dependent Interactions Between Hydrilla verticillata (L.F.) Royle and Phytoplankton: A Mesocosm Experiment

The management of submerged macrophytes is regarded as a potential method to control algal blooms. However, cell densities in algal blooms often have a wide range. Understanding interactions between varying phytoplankton cell densities and submerged macrophytes may help to develop conservation strategies. In this study, we investigated the density‐dependent interactions between the submerged macrophyte Hydrilla verticillata (L.F.) Royle and the varying concentrations of phytoplankton in an enclosed environment. Our results showed that H. verticillata controlled the density of phytoplankton in the system that maintained it at approximately 30% of the initial level, promoted high phytoplankton diversity, and attained greater biomass and plant length in the low initial phytoplankton density treatment (7.5 × 106 cells/L). In the systems without H. verticillata, phytoplankton multiplied to a density by approximately ninefolds of the initial level during the experiment period, and a number of Bacillariophyta and Chlorophyta species disappeared, which indicated decreased phytoplankton diversity. When the initial phytoplankton density was high (1.9 × 108 cells/L), H. verticillata did not effectively control phytoplankton cell density and the presence of H. verticillata did not significantly influence the final phytoplankton cell density or species composition, while the proportion of Microcystis spp. was increased. High cell density phytoplankton conditions had a negative effect on the biomass and length of H. verticillata. Initial phytoplankton cell density is an important factor that needs to be considered for predicting whether submerged macrophyte planting could inhibit the algal bloom.

Can free-floating and emerged macrophytes influence the density and diversity of phytoplankton in subtropical reservoirs?

Aquatic macrophytes and phytoplankton are important for primary production and metabolism in lentic systems. We investigated the influence of the macrophytes on the phytoplankton in a subtropical reservoir on a seasonal scale (2009–2010). Our study was one of the first to investigate the effects of free-floating and emerged macrophytes on phytoplankton assemblages in a subtropical reservoir. The concentrations of total phosphorus (25–92 μg/L) and the inflow discharge to the reservoir (6.4–54.3 m3/s) varied seasonally (p < 0.05, multivariate analysis of variance [MANOVA]) and were positively and negatively related with the macrophyte biomass, respectively (principal components analysis [PCA]). Light availability was significantly different within the sampling periods (p < 0.05) and influenced phytoplankton densities (0.6 × 103 to 21.0 × 103 ind/mL) and chlorophyll a (<0.5–51.3 μg/L). Abiotic environmental factors and macrophytes influenced the phytoplankton dynamics, and it was difficult to clearly separate these effects. Although the MANOVA did not show seasonal variation of the macrophyte biomass (p > 0.405), the PCA suggested that phytoplankton densities were inversely correlated with the biomass of most of the macrophyte species. Higher phytoplankton diversity and flagellate species were associated with greater plant biomass. Our study has management implications because (1) although not presenting significant seasonal variation, the macrophyte biomass was inversely correlated with phytoplankton densities, and (2) the presence of free-floating and emerged plants induced qualitative shifts in the phytoplankton, increasing the diversity of species. The removal of the macrophytes by management actions (e.g., mechanical removal) or natural forces (e.g., wind effect) might influence the phytoplankton community and the trophic state of subtropical reservoirs.

Dispersal, eddies, and the diversity of marine phytoplankton

Lay AbstractPhytoplankton are the “plants” of the ocean; they fix carbon dioxide from the atmosphere and make up the base of the oceanic food chain. Phytoplankton are incredibly diverse, but the reason for their high biodiversity is not well understood. Generally speaking, phytoplankton might be present in a given location either because they are “happy” and able to grow there, or if they are unable to grow there, because they have been transported in from elsewhere (i.e., via dispersal). Previous studies have suggested that “hotspots” of high phytoplankton diversity found in the most dynamic oceanic regions can be explained by dispersal. We explored this question by using a set of computer simulations of phytoplankton ecology coupled to a realistic ocean circulation. We show that dispersal can only partly explain diversity hotspots. The mixing of populations by ocean currents and eddies is important, but a plentiful supply of nutrients and variable environmental conditions also enhance phytoplankton diversity. This work has generated hypotheses that will stimulate new projects to test them in the field.

Variação temporal da comunidade fitoplanctônica em lagos urbanos eutróficos

Temporal variation of the phytoplankton community in eutrophic urban lakes. The aim of this study was to investigate the seasonal changes and temporal synchrony of phytoplankton community attributes (diversity and density) at four eutrophic urban reservoirs (Jardim Botânico lake, Vaca Brava Park lake, Rosas lake and Bosque dos Buritis lake) in the city of Goiânia, Goias State. Phytoplankton diversity was estimated by the Shannon- Winner (H') index and phytoplankton density by the Utermohl method. All lakes presented high phytoplankton diversity, ranging from H' = 0.97 (Bosque dos Buritis) to H' =4.29 (Jardim Botânico). The phytoplankton diversity of the four lakes was significantly different (F = 4.74; p < 0,001. n=4), and phytoplankton density was high, with bloom of Cyanophyceae (Bosque dos Buritis) and Chrysophyceae (Jardim Botânico). The four lakes presented low or absent synchronic phytoplankton communities (density and diversity attributes); moreover, Canonical Correspondence Analysis (CCA) also showed that the lakes presented different phytoplankton community structures, especially Jardim Botanico, which evidenced most different phytoplankton community structure. Furthermore, the other lakes presented different phytoplankton communities over at least one sampling period. These results demonstrated the importance of local factors in the structure of the phytoplankton community, such as limnologic and geomorphologic characteristics.