Phytoplankton Community Composition Research Articles

Metabarcoding analysis of microbiome dynamics during a Phaeocystis globosa bloom in the Beibu Gulf, China

Phaeocystis globosa is an ecologically important haptophyte that can form harmful algal blooms (HABs). In this study, we used 16S rDNA V3-V4 amplicon sequencing data to explore the ecological mechanisms underlying a P. globosa bloom in the Beibu Gulf, China. Using field samples collected from three time points of a bloom, we observed a distinct succession in the bacteria, archaea and phytoplankton community composition throughout the bloom. We also observed temporal variation in response to the bloom at the nucleotide level, which supports a previously underappreciated amount of intragroup variation in the niches taken up by microbes during HABs. We developed a preliminary model for the development and progression of the P. globosa bloom using the spatial-temporal dynamics of P. globosa and the bacteria, archaea, phytoplankton and environmental variables. We also identified microbes with putative interactions with P. globosa during the bloom by identifying microbes correlated with P. globosa in interaction networks, identifying particle-associated microbes and exploring the P. globosa colony microbiome using sequences from whole P. globosa colonies collected during the bloom. This study revealed novel insight into the development of P. globosa HABs and many testable hypotheses that will guide future research on the mechanisms of P. globosa HABs.

Changes in water column oxygen, estimates of productivity and the development of anoxia in a major embayment of the southern Benguela eastern boundary upwelling system

The metabolic balance of autotrophy and heterotrophy in St Helena Bay was investigated through estimates of net community production (NCP) and respiration (R), as determined by changes in water column oxygen. Compared to adjacent coastal waters St Helena Bay was shown to be an area of low-enrichment and high-retention. Productivity during the upwelling season was found to be nutrient limited in the upper few metres (0–3 m) and light limited through self-shading below these surface waters. During the upwelling season the maintenance of thermal stratification in the bay leads to consistently low nutrients (nitrate x¯ = 1.41 mmol m−3) in the surface waters (0–3 m). High biomass maintained through mechanisms of cyclonic retention and entrainment from the Namaqua shelf underlies the rapid attenuation of light through the water column and the consequent limitation of subsurface productivity. As a result productivity maxima were located in surface waters (0 or 3 m) irrespective of the low nutrient concentrations in these waters and the presence of subsurface biomass maxima. Estimates of gross community production (GCP) normalised to Chl a therefore declined sharply below 3 m depth. The mean community compensation depth (Zcc), where R = GCP, was determined to be 9.16 m and was shallower than the 1% light depth for PAR (Z1%PAR) at 15.42 m. The role of light in limiting productivity was clearly evident in that 48% of water column biomass was located below the Zcc. The importance of the light environment in controlling the seasonality of productivity was further evident in that daily rates of productivity in surface waters normalised to Chl a were clearly linked to day length. Phytoplankton community composition and successional status were also shown to influence productivity with the contribution of R to GCP increasing with the succession of phytoplankton communities. Estimates of mean water column Chl a (8.60 mg m−3 as determined from discrete water samples and 8.40 mg m−3 as estimated from profiles of fluorescence) and mean integrated water column productivity (5.38 g C m−2 d−1 as determined by the light-and-dark bottle oxygen method) were ~ 1.5 fold higher than past measurements most of which were made during the late 1970s and 80s. Oxygen depletion within St Helena Bay is locally enhanced as a result of the entrainment and retention of biomass in St Helena Bay and causes it to function as an area of higher carbon sequestration.

Phytoplankton and ecological state of Dolgoe Lake (Pskov Region)

The paper deals with the planktonic algoflora of Dolgoe Lake in the Pskov Region. The studies were carried out in the summers of 2017-2020. The taxonomic composition of the phytoplankton of the lake was revealed, including 156 species and intraspecific taxa from 8 phylums: Chlorophyta, Bacillariophyta, Cyanobacteria, Charophyta, Ochrophyta, Dinophyta, Euglenophyta, Cryptophyta. The basis of the floral complex was made up of representatives of the phylums Chlorophyta and Bacillariophyta, as well as Cyanobacteria. The greatest similarity in the species composition of phytoplankton communities was noted in 2017 and 2019 (the Sierensen-Chekanovsky coefficient was 60%), the lowest - in 2018 and 2019, as well as in 2018 and 2020 (39%). The maximum quantitative development of microalgae was noted in 2019 (32,9 million cells/l), with 90,7% of the total number accounted for cyanobacteria Merismopedia minima G. Beck. The smallest number of planktonic algae was observed in 2020 - 1,3 million cells/l. The total biomass of phytoplankton was the highest in July 2019 - 0,45 mg/l, and the lowest in 2020 - 0,15 mg/l. According to the Milius trophic index, the waters of the lake are oligotrophic. According to the ecological and geographical characteristics, widespread freshwater species of phytoplankton prevailed in the lake, preferring slightly alkaline waters. Saprobiological analysis showed that the waters of Dolgoe Lake are moderately polluted and belong to the 3rd class of quality. The saprobity index of the Pantle-Buck, depending on the year of the study, varied from 1,80 to 1,98.

OC4-SO: A New Chlorophyll-a Algorithm for the Western Antarctic Peninsula Using Multi-Sensor Satellite Data

Chlorophyll-a (Chl-a) underestimation by global satellite algorithms in the Southern Ocean has long been reported, reducing their accuracy, and limiting the potential for evaluating phytoplankton biomass. As a result, several regional Chl-a algorithms have been proposed. The present work aims at assessing the performance of both global and regional satellite algorithms that are currently available for the Western Antarctic Peninsula (WAP) and investigate which factors are contributing to the underestimation of Chl-a. Our study indicates that a global algorithm, on average, underestimates in-situ Chl-a by ~59%, although underestimation was only observed for waters with Chl-a > 0.5 mg m−3. In high Chl-a waters (>1 mg m−3), Chl-a underestimation rose to nearly 80%. Contrary to previous studies, no clear link was found between Chl-a underestimation and the pigment packaging effect, nor with the phytoplankton community composition and sea ice contamination. Based on multi-sensor satellite data and the most comprehensive in-situ dataset ever collected from the WAP, a new, more accurate satellite Chl-a algorithm is proposed: the OC4-SO. The OC4-SO has great potential to become an important tool not only for the ocean colour community, but also for an effective monitoring of the phytoplankton communities in a climatically sensitive region where in-situ data are scarce.

A biogeographic assessment of phytoplankton richness and composition in the Andaman Archipelago and the potential links to anthropogenic and environmental impacts: A multivariate approach

We report here a year-round baseline assessment on phytoplankton diversity and abundance from the pristine coastal waters of the Andaman Islands (September 2011–October 2012). A total of 84 phytoplankton species belonging to 47 genera were recorded from the North to South Andaman Islands. The maximum number of phytoplankton diversity (84 species under 47 genera) was recorded during the northeast monsoon (NEM) at a highly urbanized coastal environment like South Andaman Islands, whereas the minimum diversity (53 species under 34 genera) was recorded during the inter-monsoon (IM) period at the less anthropogenic activity sites viz. North and Middle Andaman Islands. All over seasons, the community composition of phytoplankton was mostly dominated by diatoms (45%–87%) followed by dinoflagellates (11%–46%) and blue–green algae (1%–35%). Besides, the abundance of phytoplankton was recorded as a gradual decrease from South Andaman to North Andaman Islands. The Canonical Correspondence Analysis (CCA) revealed the impact of physicochemical variables on phytoplankton assemblages. Thus, the temperature, salinity, and nitrite were the major environmental variables that influenced phytoplankton assemblage and distribution in the coastal waters of the Andaman Islands. The Principal Component Analysis (PCA) showed a strong variability of phytoplankton diversity in the South Andaman Islands (PC1: 32.6–36.2% variance). In addition, the Metric-multidimensional Scaling analysis also showed the gradual species intensity in the South Andaman than the Middle and North Andaman Islands.

Brownification reduces oxygen gross primary production and community respiration and changes the phytoplankton community composition: An in situ mesocosm experiment with high‐frequency sensor measurements in a North Atlantic bay

AbstractIn recent decades, the increase in terrestrial inputs to freshwater and coastal ecosystems, especially occurring at northern latitudes, has led to a process of water color darkening known as “brownification.” To assess how brownification affects plankton community composition and functioning in northern coastal areas, an in situ mesocosm experiment using a highly colored humic substance to simulate a brownification event was performed in a North Atlantic bay (Hopavågen, Norway) in August 2019. Manual sampling for analyses of nutrient concentrations, phytoplankton pigments and zooplankton abundances was combined with high‐frequency (every 15 min) monitoring of key environmental variables to investigate the response of the plankton community in terms of oxygen metabolism and community composition. In response to brownification, the oxygen gross primary production (GPP) and community respiration (R) slowed down significantly, by almost one‐third. However, GPP and R both decreased to the same extent; thus, the oxygen metabolic balance was not affected. Moreover, the chlorophyll‐a concentration significantly decreased under brownification, by 9% on average, and the chemotaxonomic pigment composition of the phytoplankton changed, indicating their acclimation to the reduced light availability. In addition, brownification seemed to favor appendicularians, the dominant mesozooplankton group in the mesocosms, which potentially contributed to lowering the phytoplankton biomass. In conclusion, the results of this in situ mesocosm experiment suggest that brownification could induce significant changes in phytoplankton and zooplankton community composition and significantly alter the overall oxygen metabolism of plankton communities in a northern Atlantic bay.

The effects of changes in diversity on phytoplankton community metabolism

ABSTRACT Changes in composition of phytoplankton communities cause drastic changes in functioning of aquatic ecosystems. In this study, we hypothesized that the shifts in composition of the phytoplankton community of Lake Kinneret induced notable shifts in the relationship between primary production and decomposition of organic matter in the lake ecosystem. To test this, we created an approach based on a statistical analysis of long-term dynamics of diversity indices and their relationships with potential perturbations: changes in lake water level, nutrient loads, and annual average epilimnetic temperature. Biodiversity of the algal community was estimated using Simpson’s Diversity Index and community-weighted mean trait value (functional diversity index). Specific community respiration and photosynthesis assimilation number were considered as the functional traits characterizing the role of phytoplankton in cycling organic matter. The observed temporal trends in the diversity indices provided estimates of the shift in the biotic community from large, relatively faster aerobic decomposing and slower photosynthesizing producers towards slower aerobic decomposing and faster photosynthesizing producers. These trends were confirmed by the results of direct determination of community respiration and (indirectly) by the reduced microbial activity in the epilimnetic waters of the lake.

The interactive effects of temperature and nutrients on a spring phytoplankton community

AbstractA complex interplay of environmental variables impacts phytoplankton community composition and physiology. Temperature and nutrient availability are two principal factors driving phytoplankton growth and composition, but are often investigated independently and on individual species in the laboratory. To assess the individual and interactive effects of temperature and nutrient concentration on phytoplankton community composition and physiology, we altered both the thermal and nutrient conditions of a cold‐adapted spring phytoplankton community in Narragansett Bay, Rhode Island, when surface temperature was 2.6°C and chlorophyll > 9 μg L−1. Water was incubated in triplicate at −0.5°C, 2.6°C, and 6°C for 10 d. At each temperature, treatments included both nutrient amendments (N, P, Si addition) and controls (no macronutrients added). The interactive effects of temperature and resource availability altered phytoplankton growth and community structure. Nutrient amendments resulted in species sorting and communities dominated by larger species. Under replete nutrients, warming tripled phytoplankton growth rates, but under in situ nutrient conditions, increased temperature acted antagonistically, reducing growth rates by as much as 33%, suggesting communities became nutrient limited. The temperature–nutrient interplay shifted the relative proportions of each species within the phytoplankton community, resulting in more silica rich cells at decreasing temperatures, irrespective of nutrients, and C : N that varied based on resource availability, with nutrient limitation inducing a 47% increase in C : N at increasing temperatures. Our results illustrate how the temperature–nutrient interplay can alter phytoplankton community dynamics, with changes in temperature amplifying or exacerbating the nutrient effect with implications for higher trophic levels and carbon flux.

Comparative account on phytoplankton functional community dynamics in the Alappuzha mud bank region (southwest coast of India) by HPLC-CHEMTAX and microscopy approaches

Phytoplankton community composition and its temporal dynamics were evaluated in the Alappuzha near shore waters (<15 m depth), including mud bank region, located along the southwest coast of India, using HPLC-derived marker pigments and microscope-based species composition data. The study has shown a characteristic phytoplankton succession pattern, wherein an exceptional increase in chlorophyll a (Chl a, >10 mg m−3), observed in the whole study region during the peak southwest monsoon (SWM - July) period, apparently unveiled the biological manifestation of nutrient enrichments facilitated by the coastal upwelling phenomenon. A conspicuous increase in fucoxanthin (a biomarker for diatoms) perceived across the study region clearly indicated the preponderance of diatoms (mainly Thalassiosira sp., Skeletonema costatum, Trieres mobiliensis, Nitzschia sp. etc.), particularly during the peak SWM period. The CHEMTAX calculations have shown the significant contribution of Chl a (av. 76% of total Chl a) from diatoms, regardless of seasons, compared to other taxonomic groups. Furthermore, the combined results of HPLC-CHEMTAX analyses have demonstrated the seasonal occurrence of various small-sized phytoplankton functional groups (PFGs), specifically cyanobacteria, cryptophytes and chlorophytes, along with the predominant large-sized PFGs, i.e. diatoms (mostly) and dinoflagellates. The relative increase in zeaxanthin prevalent during the warm periods (Pre-SWM and Post SWM) signified the presence of cyanobacteria. By contrast, during the SWM period, a conspicuous increase in Chl b and alloxanthin recorded in the whole study region indicated the abundance of green algae and cryptophytes, respectively. Likewise, a nominal increase in peridinin (a marker for dinoflagellates) prevalent during the onset of SWM was apparently due to the proliferation of dinoflagellates, Tripos furca and Prorocentrum micans (microscopically confirmed). Even though the overall CHEMTAX results clearly complemented the microscopy derived phytoplankton composition data, especially the abundance of large sized PFGs, (i.e. diatoms and dinoflagellates), this particular analysis could enable the portrayal of seasonal dynamics of small-sized PFGs (mainly cyanobacteria and cryptophytes) as well, as this information is highly significant as far as the study region is concerned.

Impact of salinity variation and silicate distribution on phytoplankton community composition in Pearl River estuary, China

Monitoring the primary producer diversity is crucial in understanding ecosystems balance, as imbalanced nutrients richness and diversity may induce red tide situations. The present study deals with evaluating the impact of hydrological factors regulating the dynamics of phytoplankton communities and the influence of chemical parameters on phytoplankton growth in Pearl River Estuary (PRE). During wet season (April), around 50 different species of phytoplankton were identified at 14 different sampling sites including 24 diatoms, 9 dinoflagellates, 10 green algae and 6 cyanobacterial species respectively. The diatom Melosira granulate was the dominant species at most of the sampling sites. Phytoplankton surveys during the dry season (November) showed Bellerochea malleus and Skeletonema costatum species as dominant at most of the sampling locations. Silicate (SiO3) distribution was one of the reason for the abundance of diatoms in west shoal sites. The concentration of nutrients and hydrological factors like water depth and salinity strongly supported phytoplankton growth. In addition, PRE west and middle shoal sites showed evidence of rich phytoplankton diversity when compared to east shoal and channel sites. The Non-metric Multidimensional Scaling (NMDS) analysis and cluster grouping analysis demonstrated the uniqueness of plankton species diversity at PRE west and east shoal sites. The results of Canonical Correspondence Analysis (CCA) suggested that diversity of phytoplankton communities was significantly influenced by environmental factors such as salinity, depth and SiO3 concentration. From these results, one may conclude that salinity with SiO3 distribution plays a crucial role in PRE phytoplankton community composition assisting in maintaining healthy intertidal ecosystem.

Proliferation of phytoplankton along a 500 km transect of the St. Lawrence River from its outflow at Lake Ontario

Observation of phytoplankton and water chemistry along the main channel of the St. Lawrence River was made at a high spatial resolution (every 12 km) in order to infer the factors that influence development of this phytoplankton community. The phytoplankton community in the main channel was collected over a 10-d period (mid July 2018) from the headwaters to near the beginning of the St. Lawrence River estuary. Total phosphorus concentration in river water increased with distance downstream (154–2,750 nM) and phytoplankton biomass (1.4–10.5 µg chl-a/L) was strongly correlated (r = 0.84, 46 d.f.) to the concentration of total phosphorus. Diatoms, chrysophytes and dinoflagellates dominated the phytoplankton community at the outlet of Lake Ontario and total chlorophyll-a concentrations increased three-fold with 500 km transit downstream from Lake Ontario; phycocyanin-rich Cyanobacteria showed the greatest proportional increase (227%). Total P concentrations observed in 1997 along this transect were identical to those observed in 2018; however, chl-a concentrations were much lower in 1997, a finding attributed to a greater filter feeding benthic organism impact on the standing crop of phytoplankton. Observations support the hypothesis that the phytoplankton community composition in this large river is strongly influenced by the headwater characteristics (Lake Ontario) and gradually influenced by entrainment of nutrient-rich tributary waters.

Spatio-Temporal Dynamics in Physico-Chemical Properties, Phytoplankton and Bacterial Diversity as an Indication of the Bovan Reservoir Water Quality

The study aimed to investigate the physico-chemical properties as well as phytoplankton and bacterial community diversity of Bovan Lake reservoir in Serbia to gain insight into the seasonal dynamic of water quality. All analyses were performed at three localities and water depths in spring, summer, autumn, and winter 2019. Seven phytoplankton phyla comprising 139 taxa were detected at all three localities (Chlorophyta 58%, Bacillariophyta 14%, Cyanobacteria 9%, Chrysophyta 5%, Dinophyta 5%, Euglenophyta 5%, and Cryptophyta 4%). Winter 2019 was characterized by the presence of 36 unique species in all phyla except Euglenophyta. Bacterial diversity analyses showed that Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, and Verrucomicrobia dominated the water intake locality at all three water depths (0.5, 10, and 20 m below the surface). In general, the physico-chemical parameters, phytoplankton, and bacterial community composition depended on the season and the water depth and showed that Bovan Lake was of satisfactory ecological status and water quality at all localities, and meets the needs for all intended purposes.

Ubiquitous Occurrence of a Biogenic Sulfonate in Marine Environment

The biogenic sulfonate 2,3-dihydroxypropane-1-sulfonate (DHPS) is a vital metabolic currency between phytoplankton and bacteria in marine environments. However, the occurrence and quantification of DHPS in the marine environment has not been well-characterized. In this study, we used targeted metabolomics to determine the concentration of DHPS in the Pearl River Estuary, an in situ costal mesocosm ecosystem and a hydrothermal system off Kueishantao Island. The results suggested that DHPS occurred ubiquitously in the marine environment, even in shallow-sea hydrothermal systems, at a level comparable to that of dimethylsulfoniopropionate. The concentration of DHPS was closely related to phytoplankton community composition and was especially associated with the abundance of diatoms. Epsilonproteobacteria were considered as the most likely producers of DHPS in shallow-sea hydrothermal systems. This work expands current knowledge on sulfonates and presents a new viewpoint on the sulfur cycle in hydrothermal systems.

Microbial Growth in Shrimp Ponds as Influenced by Monosilicic and Polysilicic Acids

In order to increase shrimp production and minimize detrimental environmental impacts of aquaculture, the maintenance and regulation of the growth and composition of phytoplankton communities and nutritional balance are critical. Silicon (Si) is an essential nutrient for diatoms and other types of microorganisms, but the information about the Si impact on their growth is extremely scarce. Monosilicic and polysilicic acids were tested in several shrimp cultivation systems in Jiangsu Province, China. In pond waters, the concentrations of monosilicic and polysilicic acids were sharply reduced by 36-95% and 35-75%, accordingly, as compared with those in supply water sources. The microbial cell abundance was strongly dependent on monosilicic acid. In laboratory experiments, monosilicic acid added to pond water or probiotic solutions at 1- and 2-mM Si had a significant positive effect on cell abundance. Over three days, the concentrations of monosilicic acid decreased by 81 to 91% in pond water and by 11 to 24% in probiotic solution. In probiotic solutions, the degree of polymerization of silicic acid was more intensive than that in shrimp pond waters. The data obtained demonstrates the importance of systematic studies related to the functions of Si in shrimp aquaculture.

Microplastics can alter phytoplankton community composition

Microplastic pollution is a growing concern globally due to the risks they may pose to ecological communities. Phytoplankton are key ecological community in aquatic ecosystems providing both energy to food webs and have critical roles in ecosystem functions such as carbon cycling. To date studies on how microplastics effect phytoplankton have largely been limited to laboratory exposure studies using monocultures of algae. It remains unknown how the structure of phytoplankton communities will be influenced by growing microplastic pollution. The aim of this study was to determine how different concentrations microplastic fibers influence phytoplankton community structure. Two six-day microcosm studies were conducted testing the response of the phytoplankton community to low, medium, and high microplastics concentrations on the Georges River, Australia. The results showed the highest concentrations of microplastics significantly altered the structure phytoplankton community. These differences were largely driven by increased abundances of cyanobacteria taxa Aphanocapsa and Pseudanabaena, and to a lesser extent reduced abundances of taxa including Crucigenia and Chlamydmonas. There were no significant differences between controls and the low and medium treatments in either experiment. The high concentrations used in this experiment whilst likely rare in the environment are environmentally relevant and equivalent to some of more polluted ecosystems. The results highlight the potential risk to food webs and ecosystem functioning through altering the dynamics of primary production and provide evidence for further study examining the response of ecological communities to microplastics in the environment.

Artificial Upwelling in Singular and Recurring Mode: Consequences for Net Community Production and Metabolic Balance

Artificial upwelling of nutrient-rich waters and the corresponding boost in primary productivity harbor the potential to enhance marine fishery yields and strengthen the biological pump for sequestration of atmospheric CO2. There is increasing urgency to understand this technology as a “ocean-based solution” for counteracting two major challenges of the 21st century—climate change and overfishing. Yet, little is known about the actual efficacy and/or possible side effects of artificial upwelling. We conducted a large-scale off-shore mesocosm study (∼44 m3) in the oligotrophic waters of the Canary Islands to identify the community-level effects of artificial upwelling on a natural oligotrophic plankton community. Four upwelling intensities were simulated (approx. 1.5/3/5.7/10 μmol L–1 of nitrate plus phosphate and silicate) via two different upwelling modes (a singular deep-water pulse vs. recurring supply every 4 days) for 37 days. Here we present results on the response of net community production (NCP), metabolic balance and phytoplankton community composition (&amp;lt;250 μm). Higher upwelling intensities yielded higher cumulative NCP. Following upwelling onset, the phytoplankton community became dominated by diatoms in all treatments, but other taxa such as Coccolithophores increased later in the experiment. The magnitude of effects on the metabolic balance scaled with the amount of added deep water, leading to (i) a balanced to net-heterotrophic system in the singular and (ii) a net-autotrophic system in the recurring upwelling treatments. Accordingly, the mode in which nutrients are supplied to an oligotrophic system plays a crucial role in the ecosystem response, with recurring upwelling leading to higher long-term positive NCP than singular upwelling. These results highlight the importance of empirically measured local responses to upwelling such as community structure and metabolism, with major implications for the potential employment of artificial upwelling as an ocean-based solution to generate (primary) production.

Analysis of phytoplankton variations and community structure in Kuwait Bay, Northwestern Arabian Gulf

Environmental vicissitudes cause short-term variability in plankton dynamics. The effect would be more pronounced in shallow, semi-enclosed tidal coastal systems. Here, we analyzed diurnal fluctuations in coastal phytoplankton and environmental factors in relation to seasonal tidal cycles (October 2016, Fall and February–March 2017, Winter) in a sub-tropical coastal embayment (Kuwait Bay) in the northwestern Arabian Gulf. Water-column profiles were obtained for chlorophyll, photosynthetically active radiation (PAR), salinity, temperature, and dissolved oxygen. Winter was characterised by relatively cold, well‑oxygenated, nutrient-rich, and high saline waters than the fall. Nutrient levels were high during low tide and low during high tide. High-performance liquid chromatography (HPLC) analysis of phytoplankton marker pigments revealed the presence of twelve different phytoplankton functional groups. Diatoms and dinoflagellates were the most dominant groups with significant surface-bottom differences during both seasons. The phytoplankton biomass (Chl a) was the highest during the low light hours of the day with apparent day-night differences. The picoplankton community was mainly represented by the autotrophs Synechococcus (in Fall) and picoeukaryotes (in winter) with clear seasonal patterns. Compared to picoautotrophs, picoheterotrophic biomass was relatively high during winter. This study revealed that light availability and tidal mixing are the factors regulating variability in the phytoplankton community composition and biomass (Student’'s t-test, two-tailed; (P ≤ 0.1) in Kuwait Bay. High-resolution monitoring programs are essential to capture the natural variability of phytoplankton and its implication on the biogeochemistry of the shallow tide-dominated coastal systems.

Modeling surface ocean phytoplankton pigments from hyperspectral remote sensing reflectance on global scales

Phytoplankton community composition impacts food webs, climate, and fisheries on regional and global scales, and can be assessed at coarse taxonomic resolution from biomarker pigments measured using high-performance liquid chromatography (HPLC). Presently, satellite ocean color provides unprecedented coverage of the global surface ocean and offers reliable estimates of bulk biological properties; however, existing multispectral sensors have limited ability to provide information about phytoplankton community composition. Satellite ocean color at hyperspectral resolution (e.g., NASA's upcoming Plankton, Aerosol, Cloud, and ocean Ecosystem sensor, PACE) is expected to improve estimates of phytoplankton community composition from space. Phytoplankton impact ocean color via contributions to absorption and fluorescence (through phytoplankton pigments) and scattering, especially on narrow spectral scales (5–100 nm). Here, a global open ocean dataset of concurrent HPLC pigments and hyperspectral remote sensing reflectance (Rrs(λ)) observations is used to model phytoplankton pigment composition from optical data. Phytoplankton pigments are reconstructed from Rrs(λ) using optimized principal components regression modeling. This work demonstrates that thirteen phytoplankton pigments, representing five phytoplankton pigment groups (e.g., diatoms, dinoflagellates, haptophytes, green algae, and cyanobacteria), can be modeled from hyperspectral Rrs(λ). Spectral information needed to model each phytoplankton pigment concentration is found throughout the entire visible spectrum and the model results are best at high spectral resolution (≤5 nm). The resulting model recreates observed relationships among pigment concentrations, providing support for the designation of five pigment-based phytoplankton groups for the global open ocean. This work represents a step toward developing robust, global spectral models for phytoplankton pigment composition. However, more high-quality data from a wide range of ecosystems and environments are still needed to achieve this goal.

Geochemistry and sedimentary photopigments as proxies to reconstruct past environmental changes in a subtropical reservoir

Sediment cores were used to establish past environmental impacts associated with eutrophication, erosion and metal contamination in the subtropical Atibainha reservoir (São Paulo State, Brazil). We hypothesize that: (1) the levels of nutrients, determined by a spectrophotometric method, reflect the contributions of these elements over time and (2) changes in sedimentation rates, determined by 210Pb geochronology, and metal flows, determined by ICP-AEOS, are related to anthropic activities. Stratigraphic changes in the analysed variables were used to divide the sediment cores into three intervals, according to PCA and cluster analysis (Euclidian distances, Ward's method). Interval I, composed by the period prior to operation of the reservoir, was influenced by organic matter levels. Interval II, between 1967 and 1993 (PC2: 14.94% of the total variability), a period of minor impacts, was mainly influenced by Mn (eigenvalue of 0.71) and Zn (0.74). Interval III, which included sediment deposited between 1993 and 2015 (PC1: 60.28% of the total variability), was influenced by the highest levels of the pigments lutein (0.86), zeaxanthin (0.90) and fucoxanthin (0.65), together with total nitrogen (0.78) and sedimentation rate (0.91), suggesting changes in the phytoplankton community composition probably associated to the intensification of eutrophication and erosion processes. Despite the limitations of applying paleolimnological techniques in reservoirs and the use of pigments as proxies in regions with higher temperatures, it was observed that the anoxic conditions and the aphotic environment in the hypolimnion acted to preserve pigments associated with the groups Chlorophyta (lutein), Cyanobacteria (zeaxanthin) and Bacillariophyta (fucoxanthin). The isolated analysis of nutrients was not sufficient to make conclusive inferences regarding the eutrophication history, since the levels of TP tended to decrease over time, in contrast to an increase in the levels of TN. Despite intensification of eutrophication and erosion, associated to anthropic activities, no signs of metal contamination were recorded.

Harmful Algal Bloom Species in the St. Martin River: Surveying the Headwaters of Northern Maryland's Coastal Bays

Wolny, J.L.; McCollough, C.B.; Rosales, D.S., and Pitula, J.S., 2022. Harmful algal bloom species in the St. Martin River: Surveying the headwaters of northern Maryland's coastal bays. Journal of Coastal Research, 38(1), 86–98. Coconut Creek (Florida), ISSN 0749-0208. In the spring seasons of 2015 through 2017, the Maryland Department of Natural Resources and the University of Maryland Eastern Shore monitored the phytoplankton community of the headwaters of the St. Martin River, a tributary at the northern end of Maryland's coastal bays, to determine the presence and extent of harmful algal bloom (HAB) species. The phytoplankton community composition, including HAB species, was examined via weekly sampling from March through June. In 2015, HAB events began in late March with a bloom of Gymnodinium aureolum, representing the first report of this species in Maryland waters. Following the G. aureolum bloom, blooms of other HAB species occurred, including Dinophysis acuminata, Karlodinium veneficum, Prorocentrum minimum, and a species in the Alexandrium minutum complex. Initiating at the NW extent of the St. Martin River, these blooms became distributed both temporally and spatially throughout the study area. These same species were detected in 2016 and 2017 but at lower concentrations than those seen in 2015. High concentrations and diverse blooms of HAB species in 2015 may have been due to significant rain events and/or an increase in ammonium levels from a legacy nutrient pool following the removal of the Bishopville Dam, located upstream of the study site in November 2014. This study provides a baseline assessment for future work on harmful algae in the St. Martin River watershed and a look into phytoplankton community dynamics after a dam removal.