Patterns in Alpha and Beta Phytoplankton Diversity along a Conductivity Gradient in Coastal Mediterranean Lagoons

Protist taxonomic and functional diversity in aquatic ecosystems of the Brazilian Atlantic Forest

The Brazilian Atlantic Forest and its associated ecosystems are highly biodiverse but still understudied, especially with respect to eukaryotic microbes. Protists represent the largest proportion of eukaryotic diversity and play important roles in nutrient cycling and maintenance of the ecosystems in which they occur. However, much of protist diversity remains unknown, particularly in the Neotropics. Understanding the taxonomic and functional diversity of these organisms is urgently needed, not only to fill this gap in our knowledge, but also to enable the development of public policies for biological conservation. This is the first study to investigate the taxonomic and trophic diversity of the major protist groups in freshwater systems and brackish coastal lagoons located in fragments of the Brazilian Atlantic Forest by DNA metabarcoding, using high-throughput sequencing of the gene coding for the V4 region of the 18S rRNA gene. We compared α and β diversity for all protist communities and assessed the relative abundance of phototrophic, consumer, and parasitic taxa. We found that the protist communities of coastal lagoons are as diverse as the freshwater systems studied in terms of α diversity, although differed significantly in terms of taxonomic composition. Our results still showed a notable functional homogeneity between the trophic groups in freshwater environments. Beta diversity was higher among freshwater samples, suggesting a greater level of heterogeneity within this group of samples concerning the composition and abundance of OTUs.Ciliophora was the most represented group in freshwater, while Diatomea dominated diversity in coastal lagoons.

Phytoplankton Community in Relation to Environmental Variables in the Tidal Mangrove Creeks of the Pasur River Estuary, Bangladesh

The Pasur River estuary (PRE) provides vital fishery resources and supports millions of livelihoods in the southwestern coastal region of Bangladesh. Our research focused on phytoplankton community assemblages, alpha diversity indices, and the seasonal succession of major phytoplankton species in relation to physicochemical parameters in the tidal mangrove creeks of the Pasur River estuary. Spatial and temporal variations were assessed by water sampling at 17 stations in the study area from January to December 2019. The mean salinity level in the tidal mangrove creeks of the PRE was significantly (p < 0.05) higher during the dry season than during the wet season. Spatially, no significant variation (p > 0.05) was observed in the dissolved inorganic nitrogen and dissolved inorganic phosphorus between PRE and mangrove creeks, but temporally, the variables varied significantly (p < 0.05). Spatially, no significant variation (p > 0.05) was observed in the alpha diversity of the phytoplankton community but significantly (p < 0.05) varied temporally. Blue-green algae became dominant in the oligohaline conditions during the wet season, while diatoms were dominant during the dry season which severely depleted dissolved silica. In terms of phytoplankton species diversity, our study classifies the study areas as highly diversified zones. Phytoplankton succession from diatoms (dry season) to blue-green algae (wet season) is attributed to the changes in the physicochemical and nutrient parameters depending on seasonal environmental parameter fluctuations. This study illustrated that phytoplankton diversity and density varied with the degrees of habitat and seasonal changes, implying the potential impacts of anthropogenic activities and natural causes on their community structure in tropical estuaries and mangrove creeks.

Microbial diversity and ecological interactions of microorganisms in the mangrove ecosystem: Threats, vulnerability, and adaptations

Mangroves are among the world's most productive ecosystems and a part of the "blue carbon" sink. They act as a connection between the terrestrial and marine ecosystems, providing habitat to countless organisms. Among these, microorganisms (e.g., bacteria, archaea, fungi, phytoplankton, and protozoa) play a crucial role in this ecosystem. Microbial cycling of major nutrients (carbon, nitrogen, phosphorus, and sulfur) helps maintain the high productivity of this ecosystem. However, mangrove ecosystems are being disturbed by the increasing concentration of greenhouse gases within the atmosphere. Both the anthropogenic and natural factors contribute to the upsurge of greenhouse gas concentration, resulting in global warming. Changing climate due to global warming and the increasing rate of human interferences such as pollution and deforestation are significant concerns for the mangrove ecosystem. Mangroves are susceptible to such environmental perturbations. Global warming, human interventions, and its consequences are destroying the ecosystem, and the dreadful impacts are experienced worldwide. Therefore, the conservation of mangrove ecosystems is necessary for protecting them from the changing environment-a step toward preserving the globe for better living. This review highlights the importance of mangroves and their microbial components on a global scale and the degree of vulnerability of the ecosystems toward anthropic and climate change factors. The future scenario of the mangrove ecosystem and the resilience of plants and microbes have also been discussed.

Algal migration and nutrient enrichment contribute to patterns in phytoplankton versus epiphyton communities

Algal dominance between phytoplankton and epiphyton plays an essential role in predicting shallow lake shifts between clear-water and turbid-water states. However, compared to resources competition, studies on algal life-form shifts between phytoplankton and epiphyton have traditionally received less interest, as few studies have focused on algal communities in both habitats concurrently. We conducted a 4 × 3 factorial design microcosm experiment to explore the mutual feedback relationship between phytoplankton and epiphyton. The initial algal life-form (epiphytic algae and phytoplanktonic algae alone or together) and nutrients enrichment (ambient, enrichment with N and P alone or together) were manipulated. After 28 days of incubation, the results suggested that the nutrient effects on the phytoplankton and epiphyton communities differed among the three different initial algal life-forms. A significant competitive advantage of phytoplankton was found even in treatments containing only epiphytic algae as the initial algal community. The contribution of nutrient enrichment to phytoplankton abundance (13%) was similar to that of epiphyton abundance (11%). In the mutual influence between two algal communities, epiphyton was likely to be a beneficiary as the phytoplankton community contributed 15% of the variance in epiphyton abundance. In addition, significant algal life-form shifts between phytoplankton and epiphyton only occurred in treatments containing one algal life-form, but not in treatments containing both algal life-forms at the beginning of the experiment. Our results emphasized the competitive advantage of phytoplankton in utilizing nutrient resources in the water column of shallow lakes. Moreover, we demonstrated that algal life-form shift was an adaptive behavior closely correlated with environmental variation. These results will provide broader insights to explore algal succession between phytoplankton and epiphyton in shallow lakes. To better understand the mutual influence mechanism between two algal life-forms under different nutrient conditions, research on multiple short time-scales based on algal migration is needed in the future.

Air-dispersed aquatic microorganisms show establishment and growth preferences in different freshwater colonisation habitats

We attempted to mimic aeolian ecosystems to examine how filters posed by regional characteristics can influence the establishment and growth of airborne microcolonisers of a common air source. Using a natural single source of aerosols we applied a combined microscopy and high-throughput sequencing approach to examine the diversity, settling and growth potential of air-dispersed microbes in water containers representing newly formed aquatic colonisation habitats of different trophic states and salinity. Heterotrophic microeukaryotes were favoured as initial settlers when nutrients were low, while autotrophs rapidly proliferated in the high-nutrient containers, possibly due to favourable germinating conditions for their preferred mode of dispersal with resting spores. Following settling of colonisers, we investigated two contrasting hypotheses: if the different water colonisation habitats harboured the same microbial communities after establishment and growth periods, this would point towards a selection of best-fit cosmopolitan colonisers, regardless of habitat-specific characteristics. Alternatively, community dissimilarities after the growth period would suggest a selection of settlers due to bottom-up controls combined with priority effects. Both analyses suggested that the structure of the microbial communities in the different colonisation habitats were driven by nutrient content and salinity, showing clustering to similar bottom-up forces and dissimilarities in significantly different colonisation habitats.

Phytoremediation of CYN, MC-LR and ANTX-a from Water by the Submerged Macrophyte Lemna trisulca

Cyanotoxins are harmful to aquatic and water-related organisms. In this study, Lemna trisulca was tested as a phytoremediation agent for three common cyanotoxins produced by bloom-forming cyanobacteria. Cocultivation of L. trisulca with Dolichospermum flos-aquae in BG11 medium caused a release of the intracellular pool of anatoxin-a into the medium and the adsorption of 92% of the toxin by the plant-after 14 days, the total amount of toxin decreased 3.17 times. Cocultivation with Raphidopsis raciborskii caused a 2.77-time reduction in the concentration of cylindrospermopsin (CYN) in comparison to the control (62% of the total pool of CYN was associated with the plant). The greatest toxin limitation was noted for cocultivation with Microcystis aeruginosa. After two weeks, the microcystin-LR (MC-LR) concentration decreased more than 310 times. The macrophyte also influenced the growth and development of cyanobacteria cells. Overall, 14 days of cocultivation reduced the biomass of D. flos-aquae, M. aeruginosa, and R. raciborskii by 8, 12, and 3 times, and chlorophyll a concentration in comparison to the control decreased by 17.5, 4.3, and 32.6 times, respectively. Additionally, the macrophyte stabilized the electrical conductivity (EC) and pH values of the water and affected the even uptake of cations and anions from the medium. The obtained results indicate the biotechnological potential of L. trisulca for limiting the development of harmful cyanobacterial blooms and their toxicity.

Phytoplankton alpha diversity indices response the trophic state variation in hydrologically connected aquatic habitats in the Harbin Section of the Songhua River

The relationship between biodiversity and ecological functioning is a central issue in freshwater ecology, but how this relationship is influenced by hydrological connectivity stress is still unknown. In this study we analyzed the dynamic of the phytoplankton alpha diversity indices and their relationships with trophic state in two hydrologically connected aquatic habitats (Jinhewan Wetland and Harbin Section of the Songhua River) in the Songhua River Basin in northeast China. We hypothesized that the phytoplankton alpha-diversity indices have the potential to provide a signal linking trophic state variation in hydrologically connected aquatic habitats. Our results showed the Cyanophyta and Bacillariophyta were abundant at most stations. T-test showed that phytoplankton alpha diversity indices varied significantly between rainy season and dry season. Trophic State Index recorded that a meso-trophic to eutrophic states of two connected habits during study period. Multivariate statistical analysis revealed that the dynamic of phytoplankton alpha diversity index was closely associated with trophic states change. Our result indicated that hydrological connectivity is a key factor influenced phytoplankton community assembly. In addition, it is beneficial to develop an integrated approach to appropriately describe and measure the trophic state variations of hydrologically connected aquatic habits in freshwater ecosystem.