Seasonal Phytoplankton Research Articles

Dissolved organic carbon as a driver of seasonal and multiyear phytoplankton assembly oscillations in a subtropical monomictic lake

AbstractPhytoplankton assembly dynamics in lakes are highly sensitive to variability in climate drivers and resulting physicochemical changes in lake water columns. As climate change increases the frequency of major precipitation events and droughts, many lakes experience increased inputs of colored dissolved organic carbon (CDOC) and nutrients. How these CDOC‐related changes in resources, transparency, and thermal stability affect phytoplankton assemblages, succession, and resilience is understudied, particularly in subtropical lakes. Here, we used time series, multivariate, and trait‐based functional redundancy analyses to elucidate the roles of phytoplankton in ecosystem resilience and determine potential drivers of assemblage shifts in a subtropical monomictic lake with fluctuating CDOC inputs (Lake Annie, Highlands County, Florida, USA). We found that phytoplankton assemblages and successional patterns differed between two dark‐water states (late 2005–mid‐2007, late 2012–2019) bracketing a clear‐water state (mid‐2007–late 2012), caused by shifting CDOC and nutrient concentrations associated with oscillating groundwater levels. Diatoms (Bacillariophyta), which were dominant during the two dark‐water states, nearly disappeared and were replaced by synurophytes during the clear‐water state. Assemblages had greater interannual consistency in the dark‐water states, while mean functional redundancy decreased in the clear‐water state. Seasonal phytoplankton successional changes were also more pronounced and synchronized with seasonal hydrologic shifts in the dark‐water states. Multiyear assemblage shifts occurred more quickly in clear‐to‐dark than dark‐to‐clear state transitions, suggesting phytoplankton in dark‐water states may be more resistant to state transitions or even contribute to dark‐water state resilience via feedback loops.

Variations in Seasonal Phytoplankton Assemblages as a Response to Environmental Changes in the Surface Waters of Minicoy Island, Lakshadweep

Phytoplankton, the primary producers in all aquatic systems, play an important key role in biogeochemical processes that are linked to higher trophic levels and climate variability. The spatio temporal composition and abundance of micro phytoplankton species was examined in relation to physical and chemical surface water variables (i.e., Salinity, temperature and nutrients). The primary objectives of the study were to observe the variations in phytoplankton species assemblages as a response to environmental variables. Hierarchiel cluster analysis and non-metric multidimensional scaling were used to find out distinct seasonal groups based on the composition of phytoplankton. The results indicate that several key environmental factors like temperature, salinity and nutrients like nitrate, nitrite, phosphate and silicate influenced seasonal phytoplankton assemblages within the lagoon waters. The distribution of phytoplankton population showed main groups where the blue green algae populations favored the warmer conditions of pre-monsoon period, whereas the diatom population primarily flourished in the post monsoon and monsoon period. The present study deals with the phytoplankton community structure in the Indian Ocean, Lakshadweep Archipelago, Minicoy Island, particularly in the surface water with respect to environmental variables to understand the region-specific dominant community and its governing environmental settings.

Independent components of spatial-temporal structure of chlorophyll a patterns in the upper layer of the north-western shelf of the Black Sea

In the present study, the results of independent component decomposition of satellite-derived chlorophyll a (Chla) patterns for the north-western part of the Black Sea are presented. The study has been carried out on the basis of the DINEOF-reconstructed dataset of 8-day average log-transformed Chla (alChla) patterns for 1997-2016. The alChla patterns were decomposed into six independent components of its spatio-temporal variability in the north-western shelf of the Black Sea. The independent components reflect the spatial distribution of alChla anomalies which are likely to be formed under the influence of sea circulation factors driven by wind. The paper presents the results of the analysis of the intra-annual variability of independent components. The interpretation of the patterns of intra-annual independent components variability is given, taking into account the seasonal variability of the wind factor, the flow of the Danube, the Dnieper and Southern Bug rivers and the fact of modulation of independent components dynamics by seasonal phytoplankton succession.

Relative roles of fundamental processes underpinning PEG dynamics in dimictic lakes as revealed by a self-organizing, multi-population plankton model

The longstanding PEG (Phytoplankton Ecology Group) qualitative/conceptual model describes generalized seasonal phytoplankton dynamics in temperate lakes and suggests important mechanisms driving these processes. In the research presented here, we re-created the conceptual PEG dynamics using a novel mechanistic numerical plankton model. The numerical model incorporates only a handful of interacting factors and biological rules. Key model features include seasonally variable temperature, mixing depth, and light, dynamic zooplankton and phytoplankton populations, and multiple dynamic nutrient concentrations. The model design is unique in that it incorporates a population-rich phytoplankton assemblage where life-history traits of members are based on ecological principles (trade-offs between traits), allowing the assemblage to organize over time based on nutrient competition and grazing. Using 50th year solutions to the model solved with fourth-order Runge-Kutta methods, i.e., a period when the dynamics had reached stable non-equilibrium states, sensitivity analyses were run by individually varying model parameters +/- 50% and comparing the effect on model responses of interest. Simulation analyses revealed the important role light and temperature limitation played both early and late in the year controlling plankton biomass. Trade-offs in phytoplankton life-history characteristics determined the composition of the spring bloom under non-nutrient limiting conditions (fast-growing, edible populations dominated) and the post clear-water phase assemblage under low nutrient conditions (slower-growing, less-edible populations dominated). Grazer characteristics, specifically rate of grazing and spring “emergence”, determined the occurrence of the clear-water phase and influenced the post assemblage composition, where a clear-water phase was absent when the grazing rate was low or spring emergence absent, and the highly inedible populations were lost from the assemblage. Hydraulic flushing also played an important role where diminished inflow led to higher richness, evenness and diversity due to greater overwintering of less-edible taxa, which influenced phytoplankton composition during spring bloom, diminishing secondary productivity. These results increase understanding of the relative roles of fundamental mechanisms structuring natural aquatic ecosystems and reinforce the significance of key biotic and abiotic system components of temperate lakes.

Implications of flow regulation for habitat conditions and phytoplankton populations of the Nakdong River, South Korea

Anthropogenic regulation of hydrographs is a widespread approach to river management; however, the effects of river regulation on habitat conditions and aquatic communities have rarely been studied. In this study, we analyzed the physical, chemical, and biological data from the lower Nakdong River in South Korea from 2005 to 2009 before weir construction and from 2012 to 2016 after weir construction. A partial least square path model (PLS-PM) was applied to delineate the complex interrelationships of diatoms and cyanobacteria with physicochemical parameters, nutrients, zooplankton grazing, and hydrological parameters. Inferential modeling using the hybrid evolutionary algorithm (HEA) allowed the identification of differences in the importance and threshold conditions of population dynamics drivers of diatoms and cyanobacteria before and after flow regulation. The annually averaged trajectories of limnological variables displayed significant shifts in seasonality and magnitudes of phytoplankton, zooplankton, and nutrient concentrations between the two periods. The results of PLS-PM indicated that, after flow regulation, diatoms and cyanobacteria were directly affected by nutrients and zooplankton densities and the path coefficients of hydrological parameters decreased or even were insignificant. The inferential models suggested that diatom dynamics were essentially shaped by threshold conditions of water temperature (WT) and pH before regulation, but mainly by those of rotifers (below 51.1 ind. L−1) after regulation. As for cyanobacteria dynamics, WT was identified as a critical threshold condition before and after regulation, and the threshold of PO4− concentration above 145.4 L−1 was identified as the reason for occasional blooms during the post-regulation period. Overall, the results suggest that flow regulation gradually alters habitat conditions typically of rivers to those of stagnant waters. These findings must be taken into account for sustainable management strategies of regulated rivers.

Metagenomic analysis provides functional insights into seasonal change of a non-cyanobacterial prokaryotic community in temperate coastal waters.

The taxonomic compositions of marine prokaryotic communities are known to follow seasonal cycles, but functional metagenomic insights into this seasonality is still limited. We analyzed a total of 22 metagenomes collected at 11 time points over a 14-month period from two sites in Sendai Bay, Japan to obtain seasonal snapshots of predicted functional profiles of the non-cyanobacterial prokaryotic community. Along with taxonomic composition, functional gene composition varied seasonally and was related to chlorophyll a concentration, water temperature, and salinity. Spring phytoplankton bloom stimulated increased abundances of putative genes that encode enzymes in amino acid metabolism pathways. Several groups of functional genes, including those related to signal transduction and cellular communication, increased in abundance during the mid- to post-bloom period, which seemed to be associated with a particle-attached lifestyle. Alternatively, genes in carbon metabolism pathways were generally more abundant in the low chlorophyll a period than the bloom period. These results indicate that changes in trophic condition associated with seasonal phytoplankton succession altered the community function of prokaryotes. Our findings on seasonal changes of predicted function provide fundamental information for future research on the mechanisms that shape marine microbial communities.

Data-driven dynamics of phytoplankton blooms in a reaction–diffusion NPZ model

Abstract The causes of seasonal phytoplankton blooms in the ocean are a debated topic. The disturbance-recovery hypothesis posits that blooms are initiated when seasonally changing light and mixing conditions disrupt attractive equilibrium states in the predator–prey relationship between zooplankton and phytoplankton, leading to an accumulation in phytoplankton biomass. This paper follows up on this notion with a nutrient-phytoplankton-zooplankton (NPZ) model incorporating diffusion and depth-dependent coefficients in which we explore the nature of these attractive states. The reaction–diffusion NPZ model, incorporated with seasonal solar radiation and mixed layer depth data, simulates blooms with better timing than a related ordinary differential equations model but still leaves room for further modeling and improvement. The results of the data-driven, reaction–diffusion model aid in understanding the driving forces of the simulated phytoplankton blooms. The results also reveal a significant influence on the vertical structure of plankton concentration by the attenuation of light with depth in the ocean. Models that accurately simulate blooms tend to share characteristics of the reaction–diffusion model in this paper. The dynamics described in this paper could be a key mechanism that seasonally disrupts the ecological balance between phytoplankton and zooplankton and facilitates a high-latitude marine phytoplankton bloom.

Response of the phytoplankton community to seasonal and spatial environmental conditions in the Haldia port ecosystem located in the tropical Hooghly River estuary.

The phytoplankton community structure exhibits seasonal and spatial variations in response to the environmental conditions, which aids in understanding the ecosystem's health. Given this, four samplings were conducted between October 2013 to April 2015, encompassing the monsoon, post-monsoon, and pre-monsoon seasons, from the Haldia port ecosystem of India. The samples were collected from the flowing estuary and an extended semi-enclosed dock. We hypothesized that the seasonal phytoplankton community (diversity, abundance, and carbon biomass) response will differ based on the environmental and hydrographical characteristics of the study site. Picophytoplankton and nano-microphytoplankton dominated the phytoplankton community in terms of numbers and biomass, respectively. Bacillariophytes dominated the nano-microphytoplankton abundance and total biomass, except during the monsoon when Dinophytes contributed (inner-zone). The dominance of Bacillariophytes and Chlorophytes in the outer-zone with picophytoplankton and Dinophytes in the inner-zone indicated group-specific hydrographic preferences that supported the hypothesis. The positive correlation of the picophytoplankton abundance (pre-monsoon) with Secchi disc depth and the negative correlation of diatoms (post-monsoon) with temperature signify the seasonal role of light and temperature, respectively. The highest nano-microphytoplankton species diversity (Shannon-Wiener's index) during the pre-monsoon (inner-zone) with more rare species indicated the probable influence of stable waters with increased water transparency. However, the community was unevenly distributed in the estuary due to the high abundance of the diatom, Aulacoseira granulata. Although harmful algal blooms were not detected, the higher temperature and nutrient concentrations could have favoured potentially harmful species (Pseudonitzschia delicatissima, Dinophysis acuta) during the monsoon. The system ranged from oligo- to mesotrophic state with moderate pollution levels (Carlson's Trophic State Index and Shannon's Index), indicating a reduction of the nutrient accumulation effects by the existing water renewal frequency. This study recommends incorporating qualitative and quantitative phytoplankton assessment in ecological monitoring of the stable coastal sites to prevent future harmful algal episodes.

Viral lysis modifies seasonal phytoplankton dynamics and carbon flow in the Southern Ocean

Phytoplankton form the base of marine food webs and are a primary means for carbon export in the Southern Ocean, a key area for global pCO2 drawdown. Viral lysis and grazing have very different effects on microbial community dynamics and carbon export, yet, very little is known about the relative magnitude and ecological impact of viral lysis on natural phytoplankton communities, especially in Antarctic waters. Here, we report on the temporal dynamics and relative importance of viral lysis rates, in comparison to grazing, for Antarctic nano- and pico-sized phytoplankton of varied taxonomy and size over a full productive season. Our results show that viral lysis was a major loss factor throughout the season, responsible for roughly half (58%) of seasonal phytoplankton carbon losses. Viral lysis appeared critically important for explaining temporal dynamics and for obtaining a complete seasonal mass balance of Antarctic phytoplankton. Group-specific responses indicated a negative correlation between grazing and viral losses in Phaeocystis and picoeukaryotes, while for other phytoplankton groups losses were more evenly spread throughout the season. Cryptophyte mortality was dominated by viral lysis, whereas small diatoms were mostly grazed. Larger diatoms dominated algal carbon flow and a single ‘lysis event’ directed >100% of daily carbon production away from higher trophic levels. This study highlights the need to consider viral lysis of key Antarctic phytoplankton for a better understanding of microbial community interactions and more accurate predictions of organic matter flux in this climate-sensitive region.

Spatially varying phytoplankton seasonality on the Northwest Atlantic Shelf: a model-based assessment of patterns, drivers, and implications

Abstract The signal of phytoplankton responses to climate-related forcing can be obscured by the heterogeneity of shelf seascapes, making them difficult to detect from fragmented observations. In this study, a physical–biological model was applied to the Northwest Atlantic Shelf to capture the seasonality of phytoplankton. The difference in phytoplankton seasonality between the Mid-Atlantic Bight (MAB) and the Gulf of Maine (GoM) is a result of the interplay between nutrients and temperature: In the MAB, relatively high temperature in the cold season and longer oligotrophic environment in the warm season contribute to an earlier winter bloom and a later fall bloom; in the GoM, low temperature and strong mixing limit phytoplankton growth from late fall to early spring, resulting in a later spring bloom and an earlier fall bloom. Although the temperature difference between the GoM and the MAB might decrease in the future, stratification and surface nutrient regimes in these two regions will remain different owing to distinct thermohaline structures and deep-water intrusion. The spatial heterogeneity of phytoplankton dynamics affects pelagic and benthic production through connections with zooplankton and benthic–pelagic coupling.

Phytoplankton Biomass and the Hydrodynamic Regime in NEOM, Red Sea

NEOM (short for Neo-Mustaqbal) is a $500 billion coastal city megaproject, currently under construction in the northwestern part of the Red Sea, off the coast of Tabuk province in Saudi Arabia, and its success will rely on the preservation of biodiverse marine ecosystems. Monitoring the variability of ecological indicators, such as phytoplankton, in relation to regional environmental conditions, is the foundation for such a goal. We provide a detailed description of the phytoplankton seasonal cycle of surface waters surrounding NEOM using satellite-derived chlorophyll-a (Chl-a) observations, based on a regionally-tuned product of the European Space Agency’s Ocean Colour Climate Change Initiative, at 1 km resolution, from 1997 to 2018. The analysis is also supported with in situ cruise datasets and outputs of a state-of-the-art high-resolution hydrodynamic model. The open waters of NEOM follow the oligotrophic character of the Northern Red Sea (NRS), with a peak during late winter and a minimum during late summer. Coral reef-bound regions, such as Sindala and Sharma, are characterised by higher Chl-a concentrations that peak during late summer. Most of the open waters around NEOM are influenced by the general cyclonic circulation of the NRS and local circulation features, while shallow reef-bound regions are more isolated. Our analysis provides the first description of the phytoplankton seasonality and the oceanographic conditions in NEOM, which may support the development of a regional marine conservation strategy.

Abundance and Seasonality of Phytoplankton, Zooplankton and Anuran Species in Selected Wetlands of Kogi State, Nigeria

Phytoplankton, Zooplankton and anurans play vital role in the working of wetland ecosystems as they form its dynamic food web. This study was designed to determine the abundance and seasonality of Phytoplankton, Zooplankton and Anuran species in selected wetlands of Kogi State, Nigeria. The study was performed in Abu’ja wetland in Dekina Local Government area and Egwubi seasonal wetland in Ejule, Ofu Local Government area of Kogi state. From each sampled wetlands planktons were collected with plankton net at the sites. Overall, 854 specimens of anurans, 584 from Abu’ja and 270 from Egwubi sites were collected within a period of eighteen months. The abundance of phytoplankton, zooplankton and anuran species were computed. Abundance was computed as a proportion of numbers of organisms in a group to the summation of the total number in all the groups being considered. Simpson’s index (Dominance), Gini-Simpson's, Shannon-Wiener index, Berger-Parker index, Margalef’s index, Menhinick’s index, Fisher alpha, Equitability index, Brillouin index and Chao index were all calculated following standard methods. The data collected was analyzed using the Statistical Package for Social Sciences (SPSS) version 20.0, PAST version 3.14 and Microsoft Office. Level of significance was p < 0.05. Anuran species found in both wetlands included Amietophrymus regularis, A. maculatus and Hoplobatracchus occipitalis. Phytoplankton species encountered in both study stations include Oscilatoria spp, Anabaenia spp, Anacystis spp, Spirogyra spp, Oedogonium spp, Savicular spp and Euglena spp. Zooplanktons encountered include Epiphanes spp, Philodina spp, Synchata spp, Poliathra spp, Holopedium spp, Daphnia spp, Alona spp and Bosmina spp. The abundance and seasonality of phytoplankton, zooplankton and anurans in the selected wetlands studied in Kogi state, Nigeria showed that the organisms abundance are highly influenced by the seasons in Kogi State, with its peak abundance in rainy season and very low abundance in dry season.

Diverse drivers of phytoplankton dynamics in different phyla across the annual cycle in a freshwater lake

An understanding of the annual variations in the phytoplankton community in freshwater lakes, and of the drivers responsible for these variations, is essential for lake management. In this study we collected and analyzed seasonal samples of phytoplankton and assessed environmental variables in Nansi Lake from 2011 to 2015, in order to identify the seasonal dynamics of the phytoplankton community and the main drivers in each phylum. The results showed that phytoplankton diversity in Nansi Lake followed annual cycles, which were interrupted by a water diversion in 2013. The disruption of equilibrium was clearly demonstrated by the Shannon–Wiener diversity index, Pielou’s evenness index, and Simpson’s dominance index, whereas the species richness and abundance showed resilience, maintaining regular annual cycles. The dominant species were frequently Synedra acus Kütz (Bacillariophyta), Closterium gracile Bréb (Chlorophyta), and Scenedesmus quadricauda Bréb (Chlorophyta) in summer and autumn. Non-metric multidimensional scaling (NMDS) analysis suggested that the phytoplankton was most widely distributed in summer, when conditions were more conducive to phytoplankton growth and reproduction. Redundancy analysis (RDA) indicated that the main drivers for the phytoplankton community varied in different taxonomic units. Specifically, the NP ratio and permanganate index (CODMn) had significant effects on Chlorophyta, whereas pH, dissolved oxygen (DO), and transparency significantly influenced Bacillariophyta. This study highlights the importance of seasonal phytoplankton succession and the need for identification of the main drivers in each phylum in order to achieve more effective control of phytoplankton blooms in freshwater lakes.

Assessing the Skill of a High-Resolution Marine Biophysical Model Using Geostatistical Analysis of Mesoscale Ocean Chlorophyll Variability From Field Observations and Remote Sensing

High-resolution ocean biophysical models are now routinely being conducted at basin and global-scale, opening opportunities to deepen our understanding of the mechanistic coupling of physical and biological processes at the mesoscale. Prior to using these models to test scientific questions, we need to assess their skill. While progress has been made in validating the mean field, little work has been done to evaluate skill of the simulated mesoscale variability. Here we use geostatistical 2-D variograms to quantify the magnitude and spatial scale of chlorophyll a patchiness in a 1/10th-degree eddy-resolving coupled Community Earth System Model simulation. We compare results from satellite remote sensing and ship underway observations in the North Atlantic Ocean, where there is a large seasonal phytoplankton bloom. The coefficients of variation, i.e., the arithmetic standard deviation divided by the mean, from the two observational data sets are approximately invariant across a large range of mean chlorophyllavalues from oligotrophic and winter to subpolar bloom conditions. This relationship between the chlorophyllamesoscale variability and the mean field appears to reflect an emergent property of marine biophysics, and the high-resolution simulation does poorly in capturing this skill metric, with the model underestimating observed variability under low chlorophyllaconditions such as in the subtropics.

Iron operates as an important factor promoting year-round diazotrophic cyanobacteria blooms in eutrophic reservoirs in the tropics

We hypothesize that iron availability plays an important role in driving phytoplankton structure and dynamics in tropical reservoir. This role has often been neglected in routine monitoring of water quality since the main focus has been addressed on macronutrients such phosphorus and nitrogen. To elucidate the potential regulation exerted by iron availability on phytoplankton, a limnological investigation was carried out in two neighboring eutrophic reservoirs in tropical China. Traditional physical and chemical variables were measured along with total and dissolved iron concentrations to explore how they could influence phytoplankton structure. Statistical analyses showed that dissolved iron (DFe) as well as dissolved nitrogen (DIN) and soluble reactive phosphorus (SRP) significantly explained the variance of phytoplankton assemblages in both reservoirs. We could also find that diazotrophic cyanobacteria blooms generally developed when DFe concentrations were above 0.025 mg/L. Moreover, the DFe availability in the water columns was modulated by the effects exerted by the stratification/circulation patterns on redox conditions and pH values. Anaerobic conditions favored the release of iron and phosphorus from sediments, and likely favored an enhanced nitrogen assimilation and a decrease of DIN in the epilimnion. Our results highlighted that iron functions as an important factor promoting diazotrophic cyanobacteria and driving seasonal phytoplankton succession in tropical eutrophic reservoirs, not only with a direct effect on phytoplankton growth but also indirect effect by modifying the availability of nitrogen and phosphorus.

Seasonal shifts in fatty acids and sterols in sponges, corals, and bivalves, in a southern Gulf of Mexico coral reef under river influence

Tropical coral reefs influenced by rivers are exposed to changes in turbidity, sedimentation, and wastewater discharges that might affect the growth and survival of the corals and their associated community. However, riverine nutrients and fine particulate organic matter can constitute food resources for suspension-feeding animals within reef ecosystems. Organic biomarkers from sessile suspension feeders represent their surrounding environment more reliably and can assist in monitoring the health of ecosystems. Here we evaluated the seasonal (dry and rainy) effect of natural and anthropogenic sources of organic matter on fatty acid and sterol biomarkers of sessile suspension and filter-feeding animals such as the sponge Aplysina sp., the great star coral Montastraea cavernosa, and the amber pen shell Pinna carnea in a coral reef under river influence. Sponges did not show significant differences in their fatty acid profiles between dry and rainy seasons, except for increases in fatty acids associated with the consumption of bacteria in the rainy season. However, they shifted from higher proportions of episterol, brassicasterol, and poriferasterol, which are abundant in phytoplankton, red, and brown algae, respectively, in the dry season, to higher proportions of β-sitosterol abundant in higher plants such as seagrass and mangrove, in the rainy season. In contrast, the fatty acid profile of the whole coral M. cavernosa had an 80% multivariate similarity with that of its symbiont Symbiodiniaceae, a fraction which was separated only in the rainy season. The whole coral M. cavernosa also had a higher proportion of gorgosterol, in the dry season. However, during the rainy season, the whole coral shifted from higher proportions of gorgosterol and campesterol to higher proportions of cholesterol, brassicasterol from red algae and episterol, a distinctive sterol of phytoplankton. Bivalves reflected a significant shift in their fatty acids following seasonal phytoplankton changes, but did not show seasonal changes in their sterols. Sterol profiles in sponges, corals, and bivalves were significantly different from the sterol profile in sewage. However, in the rainy season, their similarity increased compared to the dry season. Still, coprostanol, a human feces biomarker indicative of sewage input, was detected in the suspended particulate matter at the surface, but not in any of the suspension-feeding animals studied. This suggests that marine currents dispersed urban sewage before reaching benthic organisms. Alternatively, coprostanol could have been metabolized before reaching the filter feeders or by the filter feeders themselves.

Microcystins presence threatens the ecosystem health of a tropical National Park: Lagunas de Montebello, Chiapas

Anthropogenic eutrophication of tropical lakes usually develops harmful cyanobacterial blooms. As algal blooms spread, the frequency of appearance of cyanotoxin producing strains increases. Within the cyanotoxins, microcystins stand out to produce numerous cases of intoxications/fatalities of livestock and humans. Since 2003, some previously crystal-clear lakes of the “Lagunas de Montebello” National Park (LMNP), Chiapas, southern Mexico, have turned brilliant green associated with perennial cyanobacterial blooms. Although these lakes are used as drinking water supply, fisheries, irrigation, and tourism, the risk of cyanotoxins’ possible presence in these water bodies had not been evaluated. Therefore, this research aimed to measure the cyanobacterial biomass and identify and measure microcystins concentration in the LMNP eutrophic lakes. Phytoplankton was dominated by well-known cyanotoxins producing cyanobacteria (Planktothrix, Raphidiopsis, and Limnothrix). Microcystins in LMNP lakes were confirmed, while the microcystin concentration ranged from 2.0 to 5.3 µg L−1. This range indicates a relatively low probability of causing acute health effects through human consumption or recreational purposes. However, these results compel the necessity of implementing a follow-up program (nonexistent in the LMNP management plan) to measure microcystins and the whole range of cyanotoxins along an annual cycle to be able to recognize the toxins’ maximum concentrations and their potential bioaccumulation in the food web. It is also needed to investigate more accurately the seasonal phytoplankton dynamics together with all limnological parameters.

An assessment of temporal, spatial and taxonomic trends in harmful algal toxin exposure in stranded marine mammals from the U.S. New England coast.

Despite a long-documented history of severe harmful algal blooms (HABs) in New England coastal waters, corresponding HAB-associated marine mammal mortality events in this region are far less frequent or severe relative to other regions where HABs are common. This long-term survey of the HAB toxins saxitoxin (STX) and domoic acid (DA) demonstrates significant and widespread exposure of these toxins in New England marine mammals, across multiple geographic, temporal and taxonomic groups. Overall, 19% of the 458 animals tested positive for one or more toxins, with 15% and 7% testing positive for STX and DA, respectively. 74% of the 23 different species analyzed demonstrated evidence of toxin exposure. STX was most prevalent in Maine coastal waters, most frequently detected in common dolphins (Delphinus delphis), and most often detected during July and October. DA was most prevalent in animals sampled in offshore locations and in bycaught animals, and most frequently detected in mysticetes, with humpback whales (Megaptera novaeangliae) testing positive at the highest rates. Feces and urine appeared to be the sample matrices most useful for determining the presence of toxins in an exposed animal, with feces samples having the highest concentrations of STX or DA. No relationship was found between the bloom season of toxin-producing phytoplankton and toxin detection rates, however STX was more likely to be present in July and October. No relationship between marine mammal dietary preference and frequency of toxin detection was observed. These findings are an important part of a framework for assessing future marine mammal morbidity and mortality events, as well as monitoring ecosystem health using marine mammals as sentinel organisms for predicting coastal ocean changes.

Survival strategies of phytoplankton functional groups to environmental factors in a drinking water reservoir, central China

In this study, use survival strategies of phytoplankton functional groups to environmental factors in a drinking water reservoir. Survival strategies of phytoplankton in drinking water reservoirs were rarely analysed. Dynamics and survival strategies of phytoplankton community in Zhushuqiao Reservoir (Changsha, China) were studied bimonthly from April 2016 to February 2017 to fill this gap. In spring, species of CRS-strategy that adapted to low water temperature, light, and nutrient dominated. There were small individuals of opportunistic colonists of C-strategy observed before stratification. With the increase of nutrient and water temperature in summer, slightly bigger, disturbance-tolerant species of R-strategy and species of CS-strategy that adapted to stratification dominated. In winter, some species adapted to low water temperature, which were R-strategists. Key factors driven seasonal phytoplankton succession were water temperature, total phosphorus, and dissolved inorganic nitrogen. Attention should be paid to potential threats from algal bloom species with C-strategy, and future longer-term monitoring of the system and its surrounding watersheds is greatly needed.

Reconsideration of the phytoplankton seasonality in the open Black Sea

Reconsideration of the phytoplankton seasonality in the open Black Sea