Changes In Phytoplankton Community Research Articles

Variation in spectral characteristics of dissolved organic matter in inland rivers in various trophic states, and their relationship with phytoplankton

Dissolved organic matter (DOM) plays an important role in aquatic ecosystems. This study aimed to reveal the variation in spectral characteristics of DOM in inland rivers in various trophic states, and understand the relationship between spectral characteristics of DOM and phytoplankton composition in various trophic states. Our investigation was carried out on the Weihe River in Shaanxi Province, China. Three humic-like substances and one protein-like substance were identified from the DOM by examination of three-dimensional (3D) fluorescence combined with parallel factor (PARAFAC) analysis and UV–Vis spectroscopy. The trophic states in this study area ranged from mesotrophic to hyper-eutrophic (37 < Trophic States Index (TSI) < 76). As the trophic states increased, the amount of phytoplankton rose, and the dominant phylum gradually changed from bacillariophyta to cyanophyta and chlorophyta. The UVA humic-like substance C1 (λEx/Em = 250(310)/400 nm) and the protein-like substance C4 (λEx/Em = 240(280)/338), frequently found in pure cultures of various phytoplankton species, were considered to be phytoplankton secretions. As the trophic state increased, the fluorescence intensity of C1 and C4 increased, along with the rising phytoplankton biomass. The UVC humic-like substance C2 (λEx/Em = 260/480 nm), derived from a terrestrial source, did not change significantly along with the increasing trophic state. The humic-like substance C3 (λEx/Em = 270/430 nm), produced by microbial decomposition, increased significantly in individual places as the trophic state increased. We concluded that the trophic state can increase the endogenous proportion of DOM by promoting phytoplankton growth, but that the changes in phytoplankton community affected by trophic state have no direct influence on the spectral characteristics of DOM.

Seasonal and Temporal Drivers Influencing Phytoplankton Community in Kuwait Marine Waters: Documenting a Changing Landscape in the Gulf

This assessment of environmental drivers and phytoplankton community in Kuwait (Arabian Gulf) arises from a scenario in which the rapid urbanisation in recent decades has caused significant changes from pre-industrial conditions. To present these changes, we have analysed a long-term water quality dataset (1984 – 2017) and explored potential changes in a sub-set of phytoplankton community data by analyzing ten years of phytoplankton data available (2007 – 2016) for Kuwait Bay and the Northern Gulf waters. The longer-term water quality data shows that dissolved nutrient concentration, with the exception of a recent fall in SiO4, have been increasing over 30 years but with a high degree of variability reflecting the changing rate of inputs from coastal pollution and the Shatt Al-Arab River. The correlative analysis between the environmental parameters and phytoplankton in the period from 2007 to 2016 show the seasonal variability of the phytoplankton are influenced by several factors stressors including higher temperatures, coastal sewage runoff, and changing salinity. Whilst the rapid and extended nutrient enrichment data move Kuwait coastal waters into a eutrophic state, the temporal patterns highlight that recent changes in phytoplankton community are more likely to be responding to cumulative pressures of eutrophication, climate and salinity changes. The seasonal and temporal changes in the coastal phytoplankton community, alongside long term deteriorating water quality present management challenges of managing local and external pressures. Continued declines in water quality within a system that is influenced by a warming climate can potentially have long-term consequences on the resilience of the Northern Gulf environment.

Changes in community structure and photosynthetic activities of total phytoplankton species during the growth, maintenance, and dissipation phases of a Prorocentrum donghaiense bloom

The potential interactions between the bloom-forming dinoflagellates and other phytoplankton during the algal bloom cycle are interesting, while the causes for the phytoplankton community changes were not fully understood. We hypothesized that phytoplankton community structure and photosynthetic activities of total phytoplankton have their special characteristics in different phases of the algal blooms. To test this hypothesis, a survey covering the process of a Prorocentrum donghaiense bloom in coastal waters between Dongtou and Nanji Islands was carried out from 9 to 20 May 2016, and the changes in the phytoplankton community and photosynthetic activities of total phytoplankton were determined. Surface seawater was sampled for microscopic analysis of phytoplankton composition and pulse amplitude modulated (PAM) chlorophyll fluorescence analysis of photosynthetic activities of the total phytoplankton species. A total of 25, 31, and 19 phytoplankton species were identified in its growth (9–12 May), maintenance (13–18 May) and dissipation phases (19–20 May), respectively. Diatoms were dominant in terms of species number while dinoflagellates were predominant at cell abundance. Dinoflagellates were the major dominant species during three phases of the bloom based on the dominance (Y) value, whereas the dominant species extended to dinoflagellates and diatoms including P. donghaiense, Coscinodiscus argus, Gonyaulax spinifera, Cyclotella sp. and Scrippsiella trochoidea in the dissipation phase. In the maintenance phase, the average cell abundances of the total phytoplankton and P. donghaiense were consistent with the chlorophyll a (Chla) concentration in the seawater; for the diversity indices of total phytoplankton species, Simpson index (C) was the highest while Shannon index (H′) and Pielou evenness index (J′) were the lowest. Furthermore, photosynthetic activities of the total phytoplankton species represented by the effective quantum yield (Fq'/Fm') and the maximum relative electron transport rate (rETRmax) in the maintenance phase were higher than those in the growth and dissipation phases. The results indicated that the characteristics of phytoplankton community structure and photosynthetic activities could be regarded as criteria in predicting the phases of algal blooms.

Gaussian decomposition and component pigment spectral analysis of phytoplankton absorption spectra

The absorption spectrum of phytoplankton is an important bio-optical parameter for ocean color hyperspectral remote sensing; its magnitude and shape can be affected considerably by pigment composition and concentration. We conducted Gaussian decomposition to the absorption spectra of phytoplankton pigment and studied the spectral components of the phytoplankton, in which the package effect was investigated using pigment concentration data and phytoplankton absorption spectra. The decomposition results were compared with the corresponding concentrations of the five main pigment groups (chlorophylls a, b, and c, photo-synthetic carotenoids (PSC), and photo-protective carotenoids (PPC)). The results indicate that the majority of residual errors in the Gaussian decomposition are <0.001 m−1, and R2 of the power regression between characteristic bands and HPLC pigment concentrations (except for chlorophyll b) was 0.65 or greater for surface water samples at autumn cruise. In addition, we determined a strong predictive capability for chlorophylls a, c, PPC, and PSC. We also tested the estimation of pigment concentrations from the empirical specific absorption coefficient of pigment composition. The empirical decomposition showed that the Ficek model was the closest to the original spectra with the smallest residual errors. The pigment decomposition results and HPLC measurements of pigment concentration are in a high consistency as the scatter plots are distributed largely near the 1:1 line in spite of prominent seasonal variations. The Woźniak model showed a better fit than the Ficek model for Chl a, and the median relative error was small. The pigment component information estimated from the phytoplankton absorption spectra can help better remote sensing of hyperspectral ocean color that related to the changes in phytoplankton communities and varieties.

莱州湾金城海域网采浮游植物年际变化及与环境因子的关系

莱州湾金城海域网采浮游植物年际变化及与环境因子的关系

High photosynthetic rates associated with pico and nanophytoplankton communities and high stratification index in the North West Atlantic

The biological dynamics of pelagic marine ecosystems are strongly influenced by the size structure and ecological succession of phytoplankton, which in turn modifies photosynthetic efficiency. Variability in photosynthetic rates is closely coupled with changes in community structure, but it is difficult to obtain coincident data at high enough resolution to characterise these changes. In this study, we employ hierarchical cluster analysis on chlorophyll-normalised high performance liquid chromatography (HPLC) pigment concentrations from the North West Atlantic, to identify seasonal successional trends amongst phytoplankton populations. Changes in phytoplankton community were also analysed as a function of mean equivalent spherical diameter (MESD) derived from absorption measurements, photosynthetic rates, water-column stratification and temperature. Well-mixed conditions in spring to early summer were associated with populations of large cells containing high concentrations of fucoxanthin, chlorophyll-c1 and chlorophyll-c2 relative to chlorophyll-a (Chl a). As stratification increased over the course of the summer, these cells were replaced by populations dominated by chlorophyll-b, 19'-hexanoyloxyfucoxanthin, 19'-butanoyloxyfucoxanthin and divinyl chlorophyll-a, indicative of small picophytoplankton. As stratification decreased in autumn, MESD and alloxanthin increased, suggesting the presence of cryptophytes. Positive relationships were found between MESD and the quantum yield of photosynthesis (φm) for 7 out of the 8 phytoplankton clusters identified, while negative relationships between mean mixed layer photosynthetically active radiation and φm and the light limited slope of photosynthesis (αB) were observed for 4 clusters, as a result of nutrient limitation and photo-protection. The highest photosynthetic rates were associated with a pico & nanophytoplankton communities, which increased from spring to late summer as stratification intensified. By contrast, diatom communities had the lowest photosynthetic rates throughout the year. These successional patterns in the dominant phytoplankton size-class and phenology support Margalef's mandala in terms of the relationship between turbulence and community structure. The study sheds new light on assemblages dominated by smaller cells, under warm, stratified conditions, having higher photosynthetic efficiencies, which has implications for the carbon flux in the NW Atlantic.

Spatial Variability and Co-acclimation of Phytoplankton and Bacterioplankton Communities in the Pearl River Estuary, China.

Phytoplankton and bacterioplankton play significant roles in estuarine systems. It is important to demonstrate the spatial variability of bacterial and microalgal communities and understand the co-acclimation of these organisms to different environmental factors. In this study, MiSeq sequencing and morphological identification were applied to analyze the variations in bacterial and microalgal communities in the Pearl River Estuary, respectively. Molecular ecological network analysis was used to investigate the potential interactions between microalgae and bacteria and illustrate the responses of these interactions to environmental gradients. The results revealed that microalgal/bacterial communities in freshwater samples were distinct from those in mesohaline water samples. Microalgae affiliated to the genus Skeletonema dominated the mesohaline water phytoplankton communities, while Melosira was the more abundant genus in freshwater communities. Actinobacteria, Alphaproteobacteria, Betaproteobacteria, and Acidimicrobiia dominated bacterial communities in freshwater samples, while Gammaproteobacteria, Bacilli, and Synechococcophycideae were more abundant in mesohaline water samples. Tightly correlations were observed between phytoplankton and bacterioplankton. These interactions were regarded to be key factors in shaping the community structures. Further, the KEGG database and PICRUSt were used to predict the functions of bacterioplankton in the process of nitrogen cycling. The results indicated that denitrification could play an important role in nitrogen loss and might alleviate the eutrophication in the Pearl River Estuary. Collectively, the results in this study revealed that substantial changes in phytoplankton and bacterioplankton communities were correlated with the gradients of environmental parameters in the Pearl River Estuary. The results also demonstrated that the interactions between phytoplankton and bacterioplankton were important for these organisms to acclimate to changing environments.

Phytoplankton (acritarch) community changes during the Permian-Triassic transition in South China

The Permian-Triassic boundary (PTB) at ~252 Ma coincided with the largest mass extinction of the Phanerozoic. Previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records, with little attention to date given to the phytoplankton that form the base of the marine trophic web. Although the fossil record of Permian-Triassic phytoplankton is relatively poor owing to preservational factors, sufficient material is now available to evaluate secular changes in acritarch communities through the mass extinction interval. In this contribution, we evaluate diversity and abundance changes among 8 genera and 25 species of acritarchs, including large-spherical, small-spherical, long-spined, and short-spined forms ranging from the Upper Permian Clarkina yini to the Lower Triassic Isarcicella isarcica zones in eight sections representing different sedimentary facies of the South China Craton. Acritarchs declined sharply from the latest Permian (C. meishanensis Zone) to the earliest Triassic (I. staeschei Zone), with extinctions and abundance changes concentrated at two horizons, the first in the latest Permian C. meishanensis Zone (Bed 25 at Meishan D) and the second in the earliest Triassic I. staeschei Zone (Bed 28 at Meishan D), mirroring the pattern of mortality among marine invertebrates. Differences in the nature and intensity of these two extinction episodes (the second having a relatively larger effect on acritarch community composition) suggest that these events may have resulted from different types of environmental perturbations.

Reconstruction of trophic state shifts over the past 90 years in a eutrophicated lake in western Switzerland, inferred from the sedimentary record of photosynthetic pigments

Anthropogenic eutrophication can initiate vast and persistent ecosystem state changes in lakes. Such changes may be characterized by increased phytoplankton taxa variability, which can affect the effectiveness and time of lake recovery mechanisms. Lake Morat in Switzerland has undergone intense eutrophication in the twentieth century (phosphorous concentrations up to 150 μg L−1) caused by excessive nutrient loadings from agricultural intensification and urbanization. Phosphorous reduction measures since 1986, such as the ban of phosphates in detergents and decreased use of fertilizers in agriculture, have resulted in total phosphorous concentrations up to 20 μg L−1 today. Despite this drastic reduction of total phosphorous, total biomass production stays high. We investigate historical changes in the phytoplankton community during the eutrophication and re-oligotrophication periods by comparing historical limnological data with sediment pigment concentrations measured by HPLC and other geochemical proxies in a radiodated sediment core. For the last 90 years, we identified four major trophic state changes in Lake Morat. The first period (AD 1924–1937) is characterized by low pigment concentrations and nutrient inputs, with good oxygen conditions. This section represents trophic conditions before the intensive eutrophication phase. The second period (AD 1937–1970) revealed an abrupt increase in pigment concentrations with higher primary production, cyanobacteria dominance and reduced oxygen levels. Oscillaxanthin indicated a Planktothrix rubescens dominance (AD 1954–1970) with concentrations up to 800 nmol g−1 OM. Their decline after AD 1970 suggests the initiation of an intense eutrophication phase (AD 1970–1983) associated with the dominance of other cyanobacteria species, higher total phosphorous inputs, and intense anoxia. In the restoration period (AD 1983–2014), there was a shift in the phototrophic community from cyanobacteria to green algae dominance, yet some cyanobacteria species remain present. Rapid phytoplankton community changes were identified in the studied period, yet overall primary production response was low. Limnological data revealed a delay of phosphorous reduction due to phosphorous recycling from the sediments. The observation of complex lake ecosystem reactions to prolonged eutrophication and subsequent re-oligotrophication, as shown by the paleolimnological and limnological data in this study, emphasize the importance of careful lake management to revert eutrophication back to historical reference biomass values.

Phytoplankton response to climate changes and anthropogenic activities recorded by sedimentary pigments in a shallow eutrophied lake

Studies that address the potential effects of climate and anthropogenic activities on lacustrine phytoplankton succession are scarce in the shallow lakes. In the present work, the succession of phytoplankton community inferred from sedimentary pigments has been investigated; the impacts of climate and anthropogenic activities on the succession have been evaluated by the generalized additive models (GAMs) in a shallow eutrophied lake, Lake Chaohu, located eastern China. The results show that phytoplankton succession can be divided into two periods: pre-1960s and post 1960s. The mean values of ββ‑Car and Chl a increased after the 1960s at both sites sampled, from 0.013 to 0.359, and 0.013 to 1.382 μg g−1, respectively (site C4), and from 0.015 to 0.530, and 0.010 to 0.921 μg g−1, respectively (site C14), reflecting significant increases of primary productivity since the 1960s. The percentage of diatoms and dinoflagellates preserved in sediments decreased from ~90% to ~15% since the 1960s, while cyanobacteria and green algae increased from ~5% to ~35%, respectively, reflecting the shift of the lake phytoplankton community. This succession was related to construction of the Chaohu Dam in 1963, increasing discharges of anthropogenic N and P into the Lake, and a generally warming environment as reflected by increasing average air temperatures. The results of GAMs showed aquatic total phosphorus (TP) concentration is the dominant contributor to phytoplankton community change, explaining 42.74%, 40.27%, 40.77% and 72.28% of the variance of total algae, cyanobacteria, green algae, and diatoms and dinoflagellates, respectively. The positive impacts of increasing TP concentrations on abundances of total algae, cyanobacteria, and green algae were observed during periods of relatively high TP concentrations since the mid-1970s. The positive responses of total algae, cyanobacteria, green algae and diatoms and dinoflagellates to increasing average air temperatures were observed since the mid-1990s, showing that a generally warmer environment facilitated algae proliferation.

Planktonic-based assessment of the landside-dammed lake (Erzurum-Turkey)

The aim of this study was to identify the variation of plankton communities in the Tortum Lake. Changes in phytoplankton and zooplankton communities in relation to the abiotic environment were analyzed using multivariate analysis. Water samples were taken monthly from three sampling points of the Tortum Lake between June 2012 and May 2013. Water temperature (5.28-23.05°C), dissolved oxygen (1.54-13.68 mgL-1), and pH (7.22-9.01) were measured in situ. Chlorophyll-a and total orthophosphate concentrations ranged from 0.18 to 5.70 mgL-1 and from 0.01 to 0.00 mgL-1, respectively. In the Tortum Lake, Ceratium hirundinella (18%), Botryococcus braunii (51%), Chlamydomonas microsphaerella (25%), Microcystis aeruginosa (7%), Melosira varians (1%), Monoraphidium contortum (1%), Copepoda (66%), Daphnia (33%) and Keratella (1%) were found. Some species such as M. aeruginosa were increased by organic and inorganic pollution in Tortum Lake.

Seasonal variability in the abundance and stable carbon-isotopic composition of lipid biomarkers in suspended particulate matter from a stratified equatorial lake (Lake Chala, Kenya/Tanzania): Implications for the sedimentary record

We studied the distribution and stable carbon-isotopic (δ13C) composition of various lipid biomarkers in suspended particulate matter (SPM) from the water column of Lake Chala, a permanently stratified crater lake in equatorial East Africa, to evaluate their capacity to reflect seasonality in water-column processes and associated changes in the lake's phytoplankton community. This lake has large seasonal variation in water-column dynamics (stratified during wet seasons and mixing during dry seasons) with associated phytoplankton succession. We analyzed lipid biomarkers in SPM collected monthly at 5 depths (0–80 m) from September 2013 to January 2015. Seasonal variation in total phytoplankton biovolume is strongly reflected in the concentration of phytadienes, a derivative of the general photosynthetic pigment chlorophyll. The wax and wane of several specific biomarker lipids between June and December 2014 reflect pronounced phytoplankton succession after deep mixing, starting with a long and sustained chlorophyte bloom (reflected by C23:1, C25:1 and C27:1n-alkenes, and C21 and C23n-alkanes), followed by a peak in diatoms between July and October (loliolide and isololiolide), and then eustigmatophytes (C30 and C32 1,15 diols) once stratification resumes in October. Peak abundance of the C19:1n-alkene during shallow mixing of the water column in January–February 2014 can be tentatively linked to the seasonal distribution of cyanobacteria. The concentration, seasonal variability, and low δ13C values of the C28 fatty acid in the SPM suggest that this biomarker is produced in the water column of Lake Chala instead of having the typically assumed vascular plant origin. The δ13C signature of particulate carbon and all aquatic biomarkers become increasingly more negative (by up to 16‰) during mixing-induced episodes of high productivity, whereas enrichment would be expected during such blooms. This reversed fractionation may be attributed to chemically enhanced diffusion, which generates depleted HCO3− under high pH (>9) conditions, as occur in the epilimnion of Lake Chala during periods of high productivity. The influence of this process can potentially explain previously observed 13C-depleted carbon signatures in the paleorecord of Lake Chala, and should be considered prior to paleorecord interpretation of organic-matter δ13C values derived (partially) from aquatic organisms in high-pH, i.e. alkaline, lakes.

Chlorophyll-a 연속 관측 변화 패턴에 따른 식물플랑크톤 군집 변화 분석

통영 연안 해역에서 chlorophyll-a 농도 변화 패턴과 그에 따른 식물플랑크톤 군집 변동을 파악하기 위해 62일간 연속 관측(2017년 7월 29일~9월 28일) 및 주 1~2회의 주기적인 식물플랑크톤 군집 분석을 실시하였다. 조사기간 동안 chlorophyll-a 농도가 증감하는 변화가 3회 발생하였다. 첫 번째 chlorophyll-a 농도 변화(8월 6일~14일)에서는 14~16시 급격한 증가가 반복적으로 나타났으며, 이는 식물플랑크톤 군집 중 최우점종으로 출현한 와편모조류 Alexandrium affine의 일주수직운동에 의한 결과이다. 두 번째(8월 24일~30일) 및 세 번째(9월 12일~17일) 변화는 Chaetoceros curvisetus, Skeletonema marinoi-dohrnii complex등의 규조류에 의해 증가하였으며, 이때 규조류는 event 1의 A. affine의 14~16시에 급격한 증가와 달리 특정 시간에 관계없이 증가하였다. 또한 실시간 chlorophyll-a 농도의 연속 관측을 통해 A. affine의 일주수직운동 및 특징적인 chlorophyll-a 농도 변화 양상을 찾아냈으며, 3회의 chlorophyll-a 농도에 대한 변화는 7~12일의 간격을 두고 증가하였다.

Impacts of Environmental Variables on a Phytoplankton Community: A Case Study of the Tributaries of a Subtropical River, Southern China

The phytoplankton community in the river is closely related to the location of the river and the impact of human activities. To summarize the patterns of phytoplankton community changes in rivers and to analyze the reasons for these patterns and differences, we sampled the three tributaries of the Dongjiang River at different latitudes in the dry and rainy season for three years. The results showed that the three rivers were mesotrophic, lightly eutrophic and moderately eutrophic respectively. From the south to the north, the water temperature and nutrition showed an increasing trend. In two different seasons, the differences in the water temperature and dissolved oxygen were clear. In the dry season, results of the multidimensional scaling (MDS) analysis indicated that the phytoplankton community structures in the Li River and Qiuxiang River were similar. Regardless of the number of species, the cell abundance or the dominance index, Bacillariophyta were found to be dominant. Chlorophyta was dominant in the Danshui River. In the rainy season, Bacillariophyta, Bacillariophyta-Chlorophyta and Chlorophyta-Cyanophyta became the dominant types in the Li River, Qiuxiang River and Danshui River, respectively. These different patterns in phytoplankton community variation were affected by both the water quality and temperature.

Fatty acid trophic markers in Lake Baikal phytoplankton: A comparison of endemic and cosmopolitan diatom-dominated phytoplankton assemblages

Recent changes in phytoplankton community in Lake Baikal suggest the reduction in bloom of endemic diatoms takes place. How much these changes affect primary production remains unknown. Fatty acids are suitable biomarkers of the phytoplankton food quality. In our work we present the data of the qualitative and quantitative analysis of fatty acids (FA) in net samples of Lake Baikal phytoplankton. According to microscopic analysis of the samples the main phytoplankton groups were diatoms (Bacillarophyceae), golden algae (Chrysophyceae), green algae (Chlorophyceae), and Dinophytes (Dinophyceae). Visual quantification of cells showed that Synedra acus subsp. radians, Aulacoseira islandica, Synedra ulna, and Aulacoseira baicalensis were dominant diatom species. The first three species are cosmopolitan and the last one is endemic. Gas chromatography–mass spectrometry analysis revealed that the fatty acid biomarker values reflect changes in phytoplankton community structure in Lake Baikal. The trophic markers of the phytoplankton dominated by endemic A. baicalensis were higher compared to the phytoplankton dominated by cosmopolitan S. acus subsp. radians. The long-chain essential FA (LCEFA, %DW) and FA-based food quality index (FQI) for endemic assemblage were 1.85 and 0.75, while for the cosmopolitan assemblage −0.70 and 0.28, correspondingly. Our data suggest that reduction in bloom of endemic A. baicalensis may negatively affect the Lake Baikal ecosystem due to probable lower LCEFA production and, consequently, lower total productivity of the lake.

Do current European lake monitoring programmes reliably estimate phytoplankton community changes?

Many European lakes are monitored according to the EU Water Framework Directive (WFD), with focus on phytoplankton biomass and species composition. However, the low-frequency WFD monitoring may miss short-term phytoplankton changes. This is an important issue because short-term extreme meteorological events (heat waves and heavy rain) are predicted to increase in frequency and intensity with climate change. We used records from Lake Mondsee (Austria) from 2009 to 2015 to test if a reduction from monthly to seasonal sampling affected the average annual phytoplankton biovolume. Furthermore, we combined inverted light microscopy, FlowCAM and flow cytometry to estimate the effect of sampling during extreme events on average phytoplankton biovolume. Relative to monthly sampling, seasonal sampling significantly overestimated phytoplankton biomass. A heat wave in 2015 and two episodes of heavy rain in 2015 and 2016 caused species-specific changes; biovolumes of chlorophytes and the filamentous cyanobacterium Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek increased significantly during the heat wave. Using live material with FlowCAM and flow cytometry, we detected small and fragile cells and colonies that were either ignored or underrepresented by analysing fixed samples with light microscopy. We suggest a modified sampling and analysis strategy to capture short-term changes within the phytoplankton community.

Identification of unique microbiomes associated with harmful algal blooms caused by Alexandrium fundyense and Dinophysis acuminata

Biotic interactions dominate plankton communities, yet the microbial consortia associated with harmful algal blooms (HABs) have not been well-described. Here, high-throughput amplicon sequencing of ribosomal genes was used to quantify the dynamics of bacterial (16S) and phytoplankton assemblages (18S) associated with blooms and cultures of two harmful algae, Alexandrium fundyense and Dinophysis acuminata. Experiments were performed to assess changes in natural bacterial and phytoplankton communities in response to the filtrate from cultures of these two harmful algae. Analysis of prokaryotic sequences from ecosystems, experiments, and cultures revealed statistically unique bacterial associations with each HAB. The dinoflagellate, Alexandrium, was strongly associated with multiple genera of Flavobacteria including Owenweeksia spp., Maribacter spp., and individuals within the NS5 marine group. While Flavobacteria also dominated Dinophysis-associated communities, the relative abundance of Alteromonadales bacteria strongly co-varied with Dinophysis abundances during blooms and Ulvibacter spp. (Flavobacteriales) and Arenicella spp. (Gammaproteobacteria) were associated with cells in culture. Eukaryotic sequencing facilitated the discovery of the endosymbiotic, parasitic dinoflagellate, Amoebophrya spp., that had not been regionally described but represented up to 17% of sequences during Alexandrium blooms. The presence of Alexandrium in field samples and in experiments significantly altered the relative abundances of bacterial and phytoplankton by both suppressing and promoting different taxa, while this effect was weaker in Dinophysis. Experiments specifically revealed a negative feedback loop during blooms whereby Alexandrium filtrate promoted the abundance of the parasite, Amoebophrya spp. Collectively, this study demonstrates that HABs formed by Alexandrium and Dinophysis harbor unique prokaryotic and eukaryotic microbiomes that are likely to, in turn, influence the dynamics of these HABs.

Response of primary producers to the hydrographic variability in the southern region of the California Current System

The response of primary producers to seasonal and interannual variabilities in the hydrographic conditions observed between 1997 and 2012 is analyzed for the southern portion of the California Current System (CCS). The analysis uses the optimum rate of primary productivity (PP) normalized by units of chlorophyll (Chla) in the water column (PBopt) and Chla concentration. In situ PP estimations using the 14C method were obtained as part of the seasonal cruises conducted by the Investigaciones Mexicanas de la Corriente de California program. Supplementary data included sea surface temperature (SST) as measured by the AVHRR sensor from 1985–2009. We found the mean value of PBopt to be at 5.1 ± 3.3 mg C·(mg Chla)–1·h–1, with maximum ranges of 0.5 and 17.5 mg C·(mg Chla)–1·h–1. The relationship between PBopt and SST suggested a phytoplankton community change at around 19 ºC, which characterized the transitional nature of the southern portion of the CCS. SST data suggested, on the one hand, that on average the 19 ºC isotherm is located in the vicinity of Punta Eugenia and, on the other, that its spatial variability defined the alternating cool–warm conditions. At the seasonal scale, this isotherm showed a marked latitudinal displacement (from 24ºN to 32ºN), which was observed to be even out of this range during interannual events associated with El Niño/La Niña. Under both cool-warm hydrographic conditions, the phytoplanktonic community showed large PBopt rates (~6 mg C·(mg Chla)–1·h–1). At the interannual scale, changes were associated to changes in the abundance and composition of nano-microphytoplankton. Additionally, data suggested that high PP rates during warm periods could be attributed to an enhanced picoplankton contribution.

A biomarker record of temperature and phytoplankton community structure in the Okinawa Trough since the last glacial maximum

AbstractA variety of biomarkers were examined from Ocean Drilling Program Core 1202B to reconstruct temperature and phytoplankton community structures in the southern Okinawa Trough since 20 ka. Two molecular temperature proxies ( $${\rm U}_{{37}}^{{{\rm K}\prime}} $$ and TEX86) show 5°C to ~6°C warming during the glacial-interglacial transition. Prior to the Holocene, the $${\rm U}_{{37}}^{{{\rm K}\prime}} $$ -derived temperature was generally 1°C to 4°C higher than TEX86-derived temperature. This difference, however, was reduced to &lt;1°C in the Holocene. Correspondingly, the phytoplankton biomarkers (e.g., C37:2 alkenone, brassicasterol, C30 1,15 diol, and dinosterol) indicate a shift of planktonic community structures, with coccolithophorids becoming more abundant in the Holocene at the expense of diatoms/dinoflagellates. This shift is related to the variability of nutrients, temperature, and salinity in the Okinawa Trough, likely controlled by the sea level and the intensity of the Kuroshio Current. The phytoplankton community change may have had profound implications for atmospheric CO2 fluctuations during glacial-interglacial cycles since diatoms and dinoflagellates have a higher efficiency of the biological pump than coccolithophorids.

Salinity-driven decadal changes in phytoplankton community in the NW Arabian Gulf of Kuwait.

Evaluation of hydrological data obtained between 2000 and 2013 from a time series station in Kuwait Bay (station K6) and an offshore southern location (station 18) off Kuwait showed drastic increase in salinity by 6units. We tested the hypothesis that increased salinity impacted phytoplankton community characteristics in these semiarid waters. The Arabian Gulf receives seasonal freshwater discharge in the north via Shatt Al-Arab estuary with a peak during March-July. A north to south gradient in the proportion of the freshwater exists between station A in the vicinity of Shatt Al-Arab estuary and station 18 in the southern offshore area. At station A, the proportion of freshwater was the highest (25.6-42.5%) in 1997 but decreased to 0.8-4.6% by 2012-2013. The prevailing hyperhaline conditions off Kuwait are attributed to decrease in the river flow. Phytoplankton data showed a decrease in the number of constituent taxa in the last one decade from 353 to 159 in the Kuwait Bay and from 164 to 156 in the offshore area. A shift in their biomass was caused by a decrease in diatom species from 243 to 92 in the coastal waters and from 108 to 83 in the offshore areas with a concomitant increase of smaller algae. Mutivariate agglomerative hierarchical cluster analysis, non-metric multi-dimensional scaling, and one-way analysis of similarity analyses on phytoplankton data at different taxonomic levels confirmed significant changes in their community organization on a decadal scale. These evidences support our hypothesis that the salinity-related environmental changes have resulted in a coincidental decrease in species diversity and significant changes in phytoplankton community between the years 2000-2002 and 2012-2013, off Kuwait. This in turn would affect the pelagic trophodynamics as evident from a drastic decrease in the catch landings of Tenulosa ilisha (Suboor), Carangoides sp. (Hamam), Otolithes ruber (Nowaiby), Parastromateus niger (Halwaya), and Epinephelus coioides (Hamoor) in Kuwait.