Phytoplankton Fluctuations Research Articles

Correlations Between Spatiotemporal Variations in Phytoplankton Community Structure and Physicochemical Parameters in the Seungchon and Juksan Weirs

The Yeongsan River is one of the four major rivers in South Korea. Since the construction of two weirs as part of the Four Major Rivers Project to secure water resources in 2011, issues with algal blooms have frequently arisen, prompting the Ministry of Environment of Korea to conduct continuous monitoring of water quality and algal outbreaks. This study, conducted between 2019 and 2023, examined the relationship between the phytoplankton community structure and physicochemical factors at the Seungchon and Juksan weirs. Phytoplankton were categorized into four groups (Bacillariophyceae, Chlorophyceae, Cyanophyceae, and other phytoplankton), and 20 dominant genera were selected for analysis. As microalgal species vary depending on environmental conditions, understanding the specific relationships among the microalgae observed in the study area can help explain their occurrence mechanisms and contribute to the development of effective management strategies. Therefore, we used principal component analysis (PCA) to analyze the seasonal variation patterns of the four microalgal groups and visualize key data features through dimensionality reduction. Additionally, PCA was employed to identify and visualize environmental factors related to seasonal variations in phytoplankton communities. PCA helped elucidate how different environmental factors influence phytoplankton fluctuations across seasons. We used canonical correspondence analysis (CCA) to investigate the relationships among the 20 dominant genera in each group and environmental factors. Additionally, CCA was used to analyze the relationship between the distribution of the top five dominant phytoplankton taxa in each group and various environmental factors. CCA allowed for a detailed examination of how these dominant taxa interact with environmental conditions. PCA revealed significant correlations between other phytoplankton and Chl-a in spring and Cyanophyceae and water temperature in summer. Bacillariophyceae was positively correlated with nitrogen-based nutrients but negatively with phosphate phosphorus (PO4-P). CCA revealed significant correlations between dominant genera and environmental factors. Stephanodiscus sp. was associated with nitrogen-based nutrients, whereas Microcystis sp. and Dolichospermum sp. were associated with water temperature and PO4-P. Stephanodiscus sp. affected water treatment through filtration and sedimentation issues, whereas Microcystis sp. and Dolichospermum sp. produced the toxin microcystin. These findings offer valuable insights for water quality management.

Phytoplankton Assemblage over a 14-Year Period in the Adriatic Sea: Patterns and Trends.

Considering the role of phytoplankton in the functioning and health of marine systems, it is important to characterize its responses to a changing environment. The central Adriatic Sea, as a generally oligotrophic area, is a suitable environment to distinguish between regular fluctuations in phytoplankton and those caused by anthropogenic or climatic influences. This study provides a long-term perspective of phytoplankton assemblage in the central eastern Adriatic Sea, with 14 years of continuous time series data collected at two coastal and two offshore stations. The predominant phytoplankton groups were diatoms and phytoflagellates, but their proportion varied depending on the vicinity of the coast, as evidenced also by the distribution of chlorophyll a. In the coastal environment, the phytoplankton biomass was substantially higher, with a higher proportion of microphytoplankton, while small phytoplankton accounted for the majority of biomass in the offshore area. In addition, a decreasing trend in diatom abundance was observed in the coastal waters, while such trend was not so evident in the offshore area. Using a neural gas algorithm, five clusters were defined based on the contribution of the major groups. The observed increase in diversity, especially in dinoflagellates, which outnumber diatom taxa, could be a possible adaptation of dinoflagellates to the increased natural solar radiation in summer and the increased sea surface temperature.

Modulation of Phytoplankton Uptake by Mesoscale and Submesoscale Eddies in the California Current System

AbstractEddies play a crucial role in shaping ocean dynamics by affecting material transport, and generating spatio‐temporal heterogeneity. However, how eddies at different scales modulate biogeochemical transformation rates remains an open question. Applying a multi‐scale decomposition to a numerical simulation, we investigate the respective impact of mesoscale and submesoscale eddies on nutrient transport and biogeochemical cycling in the California Current System. First, the non‐linear nature of nutrient uptake by phytoplankton results in a 50% reduction in primary production in the presence of eddies. Second, eddies shape the vertical transport of nutrients with a strong compensation between mesoscale and submesoscale. Third, the eddy effect on nutrient uptake is controlled by the covariance of temperature, nutrient and phytoplankton fluctuations caused by eddies. Our results shed new light on the tight interaction between non‐linear fluid dynamics and ecosystem processes in realistic eddy regimes, which remain largely under‐resolved by global Earth system models.

Understanding plankton ecosystem dynamics under realistic micro-scale variability requires modeling at least three trophic levels

Plankton ecosystems are complex, multi-trophic networks of biotic and abiotic interactions among physical and chemical components. Still, nutrient-phytoplankton (NP) interactions are in many cases assumed to be representative of higher trophic-level interactions in plankton ecosystems. Here, we investigate the degree to which NP interactions capture the overall dynamics of multi-trophic plankton ecosystems when accounting for realistic levels of micro-scale variability. Plankton models are typically developed based on the mean-field approach, which considers only first central moments (i.e., spatio-temporal means). Such conventional plankton models may be appropriate for meso‑ or larger-scales, but inappropriate for the highly intermittent spatial fluctuations of phytoplankton that are ubiquitous at the micro (mm) scale. Using Reynold's decomposition, the closure approach accounts for spatial variability and temporal fluctuations (higher central moments) of the phytoplankton distributions. We apply closure models of various combinations of Nutrient (N), Phytoplankton (P), and Zooplankton (Z), each with linear, hyperbolic, sigmoidal and quadratic phytoplankton mortality forms to test i) the previously advanced hypothesis ‘fluctuations enhance higher trophic level biomass in plankton models’ and ii) the suitability of nutrient-phytoplankton interactions as a proxy for higher trophic ecological processes. We find that in NP models with linear, hyperbolic and sigmoidal phytoplankton mortality (P-mortality), phytoplankton biomass (P-biomass) increases with variability, but in the NP model with quadratic P-mortality, P-biomass decreases with variability. The results are robust in the sense that similar qualitative behavior is obtained for a wide range of biologically feasible parameter sets. We investigate the characteristics of the measurable quantity coefficient of variation of phytoplanktonCVp for models with different numbers of compartments. The NP models with density-independent form (linear form) and density-dependent forms (hyperbolic, sigmoidal and quadratic) for P-mortality term behave quite opposite to each other: NP models with linear P-mortality produce coefficient of variation CVp > 1 for all stable solutions while NP models with hyperbolic, sigmoidal and quadratic P-mortality forms produce CVp < 1 for all stable solutions. Depending on the mortality rate assumed, the NP model produces qualitatively different results at both micro- and macro-scales, and therefore is unable to consistently capture the true underlying dynamics of plankton ecosystems. By contrast, NPZ models behaved consistently and supported the previously advanced hypotheses, regardless of the functional form assumed for P-mortality.

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.

Study of phytoplankton flora and its use as a biomonitoring tool to determine the water quality of Krishnasayar Lake, Burdwan, West Bengal, India

AbstractThe present study focused on biomonitoring approaches involving the phytoplankton composition, density and diversity, and their relationships, with changes in environmental variables, and to determine the pollution status of Krishnasayar Lake in the Burdwan District of West Bengal, India. A total of 29 phytoplankton taxa belonging to Chlorophyceae (13), Cyanophyceae (9), Bacillariophyceae (5) and Euglenophyceae (2) were observed. The phytoplankton density exhibited a maximum value of 12,633 cells/litre in the post‐monsoon season and a minimum value of 7,266 cells/litre in the pre‐monsoon season. The results of two multivariate proficiencies (cluster analysis; CCA) indicated the distribution of phytoplankton groups are influenced by pH, electrical conductivity, and the nitrate, phosphate, potassium and dissolved oxygen concentrations. Various diversity indices, including the Shannon–Wiener Diversity Index, Gleason Species Richness Index, Pielou Evenness Index and Naughton Dominance Index, were explored to illustrate the seasonal phytoplankton fluctuations. The Shannon–Wiener Diversity Index values (2.524, 2.331 and 2.666, respectively, for the pre‐monsoon, monsoon and post‐monsoon seasons) indicate the moderation level of pollution status of the lake. The present study also highlights biomonitoring is a reasonable technique for establishing ecological conditions of lakes by considering the organisms within them, including planktonic algae, macrophytes, benthic macroinvertebrates, crustaceans and fishes on the basis of a single indicator species or a combination thereof. The present study used planktonic algae to determine changes in surrounding environmental conditions. As some of the studied phytoplankton species exhibit specific ecological preferences, their presence can indicate the health of that system. As examples, Coelastrum microporum, Pandorina morum and Euglena viridis indicate high levels of organic pollution. Krishnasayar Lake is integrated with the Krishnasayar ecological park, being affected by large levels of anthropogenic disturbance attributable mostly to uncontrolled and careless activities of some visitors, annual cultural activities, other programmes, etc., meaning relevant management activities are needed to protect the lake from further degradation.

Strong self‐regulation and widespread facilitative interactions in phytoplankton communities

AbstractThe persistence of phytoplanktonic diversity in spite of competition for basic resources has long been a source of wonder and inspiration to ecologists. To sort out, among the many coexistence mechanisms suggested by theory and experiments, which ones actually maintain diversity in natural ecosystems, long‐term field studies are paramount.We analysed a large dataset of phytoplankton abundance time series using dynamic, multivariate autoregressive (MAR) models. Phytoplankton was counted and identified down to the genus level, every 2 weeks over 20 years, at 10 sites along the French coastline. MAR models allowed to estimate biotic interaction networks while also accounting for abiotic variables that may drive part of the phytoplankton fluctuations. We then analysed the ratio of intra to intertaxa interactions (a measure of niche differentiation), the frequency of negative versus positive interactions, and how stability metrics (both at the network and genus level) relate to network complexity and genus self‐regulation or abundance.We showed that a strong self‐regulation, with competition strength within a taxon (genus) an order of magnitude higher than between taxa, was present in all phytoplanktonic interaction networks. This much stronger intragenus competition suggests that niche differentiation—rather than neutrality—is commonplace in phytoplankton. Furthermore, interaction networks were dominated by positive net effects between phytoplanktonic taxa (on average, more than 50% of interactions were positive). While network stability (sensu resilience) was unrelated to complexity measures, we unveiled links between self‐regulation, intergenera interaction strengths and abundance. The less common taxa tend to be more strongly self‐regulated and can therefore maintain in spite of competition with more abundant ones.Synthesis. We demonstrate that strong niche differentiation, widespread facilitation between phytoplanktonic taxa and stabilizing covariances between interaction strengths should be common features of coexisting phytoplankton communities in the field. These are structural properties that we can expect to emerge from plausible mechanistic models of phytoplankton communities. We discuss mechanisms, such as predation or restricted microscale movement, that are consistent with these findings, which paves the way for further research.

大阪湾における植物プランクトンの長期変動と 有毒渦鞭毛藻Alexandrium tamarense の大増殖

大阪湾における植物プランクトンの長期変動と 有毒渦鞭毛藻Alexandrium tamarense の大増殖

Remote sensing of phytoplankton decline during the late 1980s and early 1990s in the South China Sea

ABSTRACT The duration of a single satellite deployment is insufficient to detect long-term trends in phytoplankton biomass. By integrating data from different platforms, we quantified the phytoplankton trends in the South China Sea (SCS) from the early-to-mid 1980s to the present. We focused on winter data because the sea surface temperature (SST) in winter has been increasing over the past three decades. We included data from three different eras: (1) the Coastal Zone Colour Scanner (CZCS) period (1979–1983), (2) the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) period (1998–2002), and (3) the Moderate Resolution Imaging Spectroradiometer (MODIS) period (2010–2014). There was a decline in phytoplankton (approximately 0.15 mg m−3) over the entire SCS from the CZCS period to the SeaWiFS period. The largest reduction (over 0.3 mg m−3) occurred in the northern and western SCS. After the SeaWiFS period, the phytoplankton increased by approximately 0.05 mg m−3. The largest increase was observed to the west of Luzon Strait, extending towards the east coast of Hainan Island. The fluctuations in phytoplankton from the early-to-mid 1980s to the present were consistent with the variation in the wind field rather than with the continued increase in SST. The wind speed decreased from the CZCS period to the SeaWiFS period and increased from the SeaWiFS period to the MODIS period. Moreover, the nutrient variations induced by the mixed-layer depth also contributed to the fluctuations in phytoplankton.

Chlorophyll a predictability and relative importance of factors governing lake phytoplankton at different timescales

Assessing the key drivers of eutrophication in lakes and reservoirs has long been a challenge, and many studies have developed empirical models for predicting the relative importance of these drivers. However, the relative roles of various parameters might differ not only spatially (between regions or localities) but also at a temporal scale. In this study, the relative roles of total phosphorus, total nitrogen, ammonia, wind speed and water temperature were selected as potential drivers of phytoplankton biomass by using chlorophyll a as a proxy for biomass. A generalized additive model (GAM) and a random forest model (RF) were developed to assess the predictability of chlorophyll a and the relative importance of various predictors driving algal blooms at different timescales in a freshwater lake. The results showed that the daily datasets yielded better predictability than the monthly datasets. In addition, at a daily scale, water temperature was a more important predictor of chlorophyll a than nutrients, and the importance of phosphorus was comparable to that of nitrogen. In contrast, at a monthly scale, nutrients are more important predictors than water temperature and phosphorus is a better predictor than nitrogen. This study indicates that the drivers of phytoplankton fluctuations vary at different timescales and that timescale has an influence on the relative roles of nitrogen and phosphorus limitation in lakes, which suggests that the temporal scale should be considered when explaining phytoplankton fluctuations. Moreover, this study provides a reference for the monitoring of phytoplankton fluctuations and for understanding the mechanisms underlying phytoplankton fluctuations at different timescales.

Predictability and environmental drivers of chlorophyll fluctuations vary across different time scales and regions of the North Sea

Phytoplankton concentrations display strong temporal variability at different time scales. Recent advances in automated moorings enable detailed investigation of this variability. In this study, we analyzed phytoplankton fluctuations at four automated mooring stations in the North Sea, which measured phytoplankton abundance (chlorophyll) and several environmental variables at a temporal resolution of 12–30 min for two to nine years. The stations differed in tidal range, water depth and freshwater influence. This allowed comparison of the predictability and environmental drivers of phytoplankton variability across different time scales and geographical regions. We analyzed the time series using wavelet analysis, cross correlations and generalized additive models to quantify the response of chlorophyll fluorescence to various environmental variables (tidal and meteorological variables, salinity, suspended particulate matter, nitrate and sea surface temperature). Hour-to-hour and day-to-day fluctuations in chlorophyll fluorescence were substantial, and mainly driven by sinking and vertical mixing of phytoplankton cells, horizontal transport of different water masses, and non-photochemical quenching of the fluorescence signal. At the macro-tidal stations, these short-term phytoplankton fluctuations were strongly driven by the tides. Along the Dutch coast, variation in salinity associated with the freshwater influence of the river Rhine played an important role, while in the central North Sea variation in weather conditions was a major determinant of phytoplankton variability. At time scales of weeks to months, solar irradiance, nutrient conditions and thermal stratification were the dominant drivers of changes in chlorophyll concentrations. These results show that the dominant drivers of phytoplankton fluctuations differ across marine environments and time scales. Moreover, our findings show that phytoplankton variability on hourly to daily time scales should not be dismissed as environmental noise, but is related to vertical and horizontal particle transport driven by winds and tides. Quantification of these transport processes contributes to an improved predictability of marine phytoplankton concentrations.

Temperature as a factor affecting fluctuations and predictability of the abundance of lake bacterioplankton

Prediction implies the estimation of future states of dynamical systems on the basis of time series. Unavoidable uncertainty in making predictions stems from errors and fluctuations associated with making measurements, and also from the complexity of the dynamics themselves. To be predicted, the time series have to contain some kind of repeatability, which can be exploited in the course of forecasting. In particular, even irregular time series are often characterized by the repeatability that implies fuzzy recurrences of the states of the system under study. Recently, the recurrence quantification analysis was used in order to assess numerically the horizon of predictability of chaotic fluctuations of the phytoplankton abundance in the Naroch Lakes system consisting of three reservoirs, Lake Naroch, Lake Myastro and Lake Batorino (Medvinsky et al., 2015. Chaos far away from the edge of chaos: A recurrence quantification analysis of plankton time series. Ecol. Complex., 23, 61–67). Here, we present the results of the analysis of the dynamics of bacterioplankton populations, which inhabit the Naroch Lakes. We demonstrate that the dynamics are chaotic. The horizons of predictability of the bacterioplankton dynamics are shown to be equal to 4.8 months for Small Stretch of Lake Naroch, 4.6 months for Large Stretch of Lake Naroch, 4.7 months for Lake Myastro, and 3.4 months for Lake Batorino. Chaoticity of fluctuations in population abundance can be either an immanent feature of the dynamics or be related to environmental influences. In order to evaluate the action of changes in the environment on plankton dynamics, we assessed numerically the extent to which chaotic fluctuations of bacterioplankton and phytoplankton abundances in the Naroch Lakes were synchronized with temperature oscillations. With the use of the analysis of phase relations between bacterioplankton and temperature time series we show that the chaotic bacterioplankton oscillations are synchronized with water temperature oscillations, while chaotic fluctuations of the phytoplankton abundance are not synchronized with the temperature oscillations in Lake Naroch and Lake Myastro in contrast to the phytoplankton fluctuations in Lake Batorino, the smallest of the Naroch Lakes, where phytoplankton fluctuations are phase-locked by the temperature oscillations. We conclude that temperature is the factor that has significant impact on predictability of the bacterioplankton fluctuations, while dynamics and predictability of phytoplankton dynamics can apparently be controlled not only by the temperature but also by trophic interactions and nutrient supply.

Bioavailable organic matter in seston modulating differential absorption rates by mussels

This study aims to analyze the seasonal variations in seston biochemical compounds (biopolymeric organic carbon (C-BPC), i.e. the sum of proteins, carbohydrates and lipids) in order to infer the bioavailable organic fraction controlling food absorption by mussels cultured in a Galician Ria. Different proxies for high-quality food (including C-BPC) vs. energy absorbed by mussels were explored to elucidate the validity of each proxy in an embayment of intensive mussel cultivation.Our results showed a strong correlation between C-BPC and both the organic fraction (f) and the carbon equivalent of Chloropyll-a (C-Chl-a) in the seston. This fact points to variations in C-BPC (predominantly composed of proteins) are strongly linked with the phytoplankton fluctuations, which in turn are modulated by the seasonal upwelling regime. Maximum total energy absorbed by mussels (about 97%) occurred during the spring phytoplankton bloom, when high-quality organic carbon (high C-BPC) dominated the seston. Minimum energy absorbed (56%) occurred during winter, when continental runoff and local resuspension of surface sediments reintroduce into the water column more refractory organic compounds not favourable to the mussel diet. These results allowed us to establish that parameters such as f, C-Chl-a, and C-BPC have close correlations with physiological responses in mussels and could be used as proxies for food quality. Nonetheless, the use of these high-quality food estimations should be considered according to particularities of each ecosystem.

Effects of some environmental factors on the population density and species diversity of phytoplankton in Bitter Lakes, Egypt

The assessment of the phytoplankton community structure in the Bitter Lakes during 2012–2013 indicated about 150 species belonging to 73 genera. These are classified as 89 species of diatoms, 27 dinoflagellates, 19 chlorophytes, 13 cyanophytes, and one of euglenophytes as well as one rare species of silicoflagellates. Diatoms were the leading and most dominant group forming about 81.67 % of the total number of individuals due to the high flourishing of Rhizosolenia alata variety gracillima, Thalassionema nitzschioides, Skeletonema costatum, Thalassiothrix frauenfeldii, and Chaetoceros lorenzianus. Abu-Rommanh was the most productive area in the phytoplankton counts, whereas the area of Shandoura was the lowest productive one, coincided principally with the types and amounts of pollutants as well as the highest human and fishing activities at this area of the Bitter Lakes. Seasonally, summer 2012 was the most productive season with an average of 8464 unit/L followed by autumn 2012 with an average of 6199 unit/L. Whereas, the winter and spring of 2013 were observed with approximately similar averages of 5527 and 5194 unit/L, respectively. Analysis of diversity indicated that the Bitter Lakes sustained good variations of phytoplankton species. It fluctuated between the averages of 2.4 in the spring of 2013 and 3.21 during the autumn of 2012, which may reflect the healthy state and ecosystem stability of Bitter Lakes during autumn. The results revealed that the total density of phytoplankton slightly increased from the average counts of 6286 unit/L during 2002–2003 to 6346 unit/L in the present study, while the number of species significantly increased from 108 species in 2002–2003 to 150 species in the present study. This may be due to the relative increase in the eutrophication state of the Bitter Lakes during the last 10 years. Generally, the seasonal fluctuations of phytoplankton positively correlated with the water temperature (22–24.2 °C), dissolved oxygen (4.85–11.11 mg/L), and reactive nitrate (0.04–1.00 mg/L), but it inversely correlated with the ammonium (0.05–0.2 mg/L) and reactive silicate (0.10–1.44 mg/L). The stepwise multiple regressions indicated that the reactive silicate, nitrate, and ammonium were the most effective factors that controlled the seasonal fluctuations and species diversity of phytoplankton in the Bitter Lakes during 2012–2013.

Phytoplankton variability in relation to some environmental factors in the eastern coast of Suez Gulf, Egypt.

Water samples were seasonally collected from 12 stations of the eastern coast of Suez Gulf during autumn of 2012 and winter, spring, and summer of 2013 in order to investigate phytoplankton community structure in relation to some physicochemical parameters. The study area harbored a diversified phytoplankton community (138 species), belonging to 67 genera. Four algal groups were represented and classified as Bacillariophyceae (90 species), Dinophyceae (28 species), Cyanophyceae (16 species), and Chlorophyceae (4 species). The results indicated a relative high occurrence of some species namely.; Pleurotaenium trabecula of green algae; Chaetoceros lorenzianus, Proboscia alata var. gracillima, Pseudosolenia calcar-avis, and Pseudo-nitzschia pungens of diatoms; Trichodesmium erythraeum and Pseudoanabaena limnetica of cyanophytes. Most of other algal species were fairly distributed at the selected stations of the study area. The total abundance of phytoplankton was relatively low (average of 2989 unit/L) in the eastern coast of Suez Gulf, as compared its western coast and the northern part of the Red Sea. The diversity of phytoplankton species was relatively high (2.35–3.82 nats) with an annual average of 3.22 nats in the present study. The results concluded that most of eastern coast of Suez Gulf is still healthy, relatively unpolluted, and oligotrophic area, which is clearly achieved by the low values of dissolved phosphate (0.025–0.3 μM), nitrate (0.18–1.26 μM), and dissolved ammonium (0.81–5.36 μM). Even if the occurrence of potentially harmful algae species was low, the study area should be monitored continuously. The dissolved oxygen ranged between 1.77 and 8.41 mg/L and pH values between 7.6 and 8.41. The multiple regression analysis showed that the dissolved nitrate and pH values were the most effective factors that controlled the seasonal fluctuations of phytoplankton along the eastern coast of Suez Gulf during 2012–2013.

Seasonal fluctuations of phytoplankton community and physico-chemical parameters of the north western part of the Red Sea, Egypt

Phytoplankton community structure and some environmental parameters in the coastal water of the north western part of the Red Sea were studied seasonally during 2013. A total of 145 species were recorded with clear dominance of Bacillariophyceae, which formed about 76.4% of the total phytoplankton counts with annual average of 3654cell/L and Dinophyceae (14.63%) with annual average of 700cell/L. Other algal classes; like Cyanophyceae, Chlorophyceae, Euglenophyceae and Silicoflagellates sustained low counts, forming collectively about 9.0% of the total abundance of phytoplankton. Autumn was the most productive season recording an average of 5916unit/L, followed by spring (average of 5282unit/L) and winter (average of 4329unit/L), while summer showed the lowest counts (average of 3607unit/L). The species diversity fluctuated between 3.36 in the summer and 3.97 in autumn, with an annual average of 3.76.The physico-chemical properties of surface water exhibited seasonal and spatial variations. The dissolved nitrate (0.07–2.27μM), ammonium (1.82–8.80μM), reactive silicate (0.41–5.22μM) and water salinity (39.9–42.9‰) were the most effective factors that controlled the seasonal fluctuations of phytoplankton during 2013. The multiple regression model was: phytoplankton counts=28,564+0.69NO3+0.284NH4−0.13SiO4−0.30 Salinity (M.R.=0.91, N=24 and p<0.07). This equation could be applied in the future to predict the total phytoplankton counts in the coastal waters of the northern part of the Red Sea, Egypt.

Dancing with the Tides: Fluctuations of Coastal Phytoplankton Orchestrated by Different Oscillatory Modes of the Tidal Cycle

Population fluctuations are often driven by an interplay between intrinsic population processes and extrinsic environmental forcing. To investigate this interplay, we analyzed fluctuations in coastal phytoplankton concentration in relation to the tidal cycle. Time series of chlorophyll fluorescence, suspended particulate matter (SPM), salinity and temperature were obtained from an automated measuring platform in the southern North Sea, covering 9 years of data at a resolution of 12 to 30 minutes. Wavelet analysis showed that chlorophyll fluctuations were dominated by periodicities of 6 hours 12 min, 12 hours 25 min, 24 hours and 15 days, which correspond to the typical periodicities of tidal current speeds, the semidiurnal tidal cycle, the day-night cycle, and the spring-neap tidal cycle, respectively. During most of the year, chlorophyll and SPM fluctuated in phase with tidal current speed, indicative of alternating periods of sinking and vertical mixing of algal cells and SPM driven by the tidal cycle. Spring blooms slowly built up over several spring-neap tidal cycles, and subsequently expanded in late spring when a strong decline of the SPM concentration during neap tide enabled a temporary “escape” of the chlorophyll concentration from the tidal mixing regime. Our results demonstrate that the tidal cycle is a major determinant of phytoplankton fluctuations at several different time scales. These findings imply that high-resolution monitoring programs are essential to capture the natural variability of phytoplankton in coastal waters.

Long-term trends and fine year-to-year tuning of phytoplankton in large lakes are ruled by eutrophication and atmospheric modes of variability

This study demonstrated how the impact of eutrophication in a deep lake at the southern border of the Alps (Lake Garda) was regulated by specific modes of atmospheric circulation relevant for the Mediterranean area. At the decadal scale, nutrients and phytoplankton increased concurrently since the 1970s. At the annual scale, year-to-year fluctuations in nutrients and phytoplankton were controlled through a chain of causal factors centred on deeply penetrative mixing events determining an upward transport of phosphorus from the hypolimnion to the trophogenic layers. The extent of mixing was in turn controlled by lake and air winter temperature, which were ultimately regulated by the winter fluctuations of the East Atlantic pattern (EA). In its negative state, the EA shows an intense high pressure over the West Atlantic, causing a north-easterly air flow bringing cold air from continental Europe to Mediterranean, thus favouring greater lake mixing and nutrient fertilisation. Cyanobacteria (mostly Planktothrix rubescens) were the organisms which greatly benefitted from the long-term increase in phosphorus concentrations and the year-to-year fluctuations in surface phosphorus availability controlled by the EA. Given the same availability of phosphorus in the water column, positive winter EA phases weakened the eutrophication effects and phytoplankton development.

Patterns of asynchrony for phytoplankton fluctuations from reservoir mainstream to a tributary bay in a giant dendritic reservoir (Three Gorges Reservoir, China)

Seasonal fluctuations of phytoplankton have often been regarded as one of the important cyclic events in aquatic ecosystems, and have even been emphasized as an important sign of regional climatic variability in limnology. However, few attempts have been made to examine synchrony for phytoplankton fluctuations among different habitats in a single reservoir system. The present study employed Spearman rank correlation analysis and the Mantel test to assess levels of synchrony for phytoplankton abundance and taxonomic composition from reservoir mainstream to a tributary bay (Xiangxi Bay) in a giant dendritic reservoir, China (Three Gorges Reservoir, TGR). At the selected scale, asynchronous patterns of phytoplankton were found when looking at total abundance and taxonomic composition, suggesting that regional drivers were not strong enough to synchronize phytoplankton fluctuations, and local regulators were predominant. As a riverine system, the mainstream of TGR had high levels of algal synchrony, while asynchronous patterns of phytoplankton were detected within Xiangxi Bay, which is characterized as a lacustrine system. The present study further confirmed that external hydrological disturbances strongly homogenize habitat conditions and synchronize phytoplankton fluctuations within the mainstream, while spatial divergence of phytoplankton succession depend on local habitat conditions within Xiangxi Bay. Moreover, low synchrony of phytoplankton between the mainstream and Xiangxi Bay is probably caused by spatial divergence of phytoplankton succession within Xiangxi Bay and the lack of succession in the rapidly flushed mainstream. Independently of these mechanisms possibly explaining phytoplankton fluctuations, the present study has also an applied perspective to the improvement of a long-term observation program in which phytoplankton trends at the mainstream scale could be compiled from the data set in a single site, while a set of sampling sites should be required at the Xiangxi Bay scale.

Short-term fluctuations in vegetation and phytoplankton during the Middle Eocene greenhouse climate: a 640-kyr record from the Messel oil shale (Germany)

The Palaeogene was the most recent greenhouse period on Earth. Especially for the Late Palaeocene and Early Eocene, several superimposed short-term hyperthermal events have been described, including extremes such as the Palaeocene–Eocene Thermal Maximum. Major faunal and floral turnovers in the marine and terrestrial realms were recorded in association with these events. High-resolution palynological analysis of the early Middle Eocene maar lake sediments at Messel, near Darmstadt, Germany, provides an insight into the dynamics of a climax vegetation during the Middle Eocene greenhouse climate in a time span without significant climatic excursions. Numerical techniques like detrended correspondence analysis and wavelet analysis have been applied to recognize cyclic fluctuations and long-term trends in the vegetation through a time interval of approximately 640 kyr. Based on the numerical zoning of the pollen diagram, three phases in the development of the vegetation may be distinguished. Throughout these phases, the climax vegetation did not change substantially in qualitative composition, but a trend towards noticeably less humid conditions probably in combination with a drop of the water level in the lake may be recognized. A shift in algal population from the freshwater dinoflagellate cyst Messelodinium thielepfeifferae to a dominance of Botryococcus in the uppermost part of the core is interpreted as a response to changes in acidity and nutrient availability within the lake. Time series analyses of pollen assemblages show that variations in the Milankovitch range of eccentricity, obliquity and precession can be distinguished. In addition, fluctuations in the sub-Milankovitch range are indicated. This demonstrates that floral changes during steady depositional conditions in the Middle Eocene of Messel were controlled by orbital forcing.