Changes In Phytoplankton Abundance Research Articles

Effect of water stratification and mixing on phytoplankton functional groups: a case study of Xikeng Reservoir, China

A shift in reservoir stratification and mixing significantly affects the water column ecosystem, which in turn leads to changes in phytoplankton abundance and community structure. To explore the effects of stratification and mixing on the phytoplankton community structure of a diversion reservoir, a 1-year survey was divided into a stratification period in 2020, a mixing period in 2020, and a stratification period in 2021, and redundancy analysis (RDA), variance partitioning analysis (VPA) and Pearson correlation analysis were used to analyse the key drivers affecting the phytoplankton functional groups, using Xikeng Reservoir as a case study. During the study period, 8 phyla, 69 genera and 9 major functional groups were observed in this reservoir. The dominant functional groups varied significantly, being X1 in the stratified period in 2020; P and D in the mixing period in 2020; and D, X1, and M in the stratified period in 2021. The phytoplankton diversity index was greater in the mixing period than in the stratification period, in agreement with the results of the aquatic ecological status evaluation (Q index, higher in the mixing period than in the stratification period). However, phytoplankton diversity of Xikeng Reservoir was of limited value in assessing the degree of water pollution, so should be considered in combination with the Q index. Water temperature (WT), mixing depth (Zmix), nitrogen–phosphorus ratio (N/P), and total nitrogen (TN) were important drivers of phytoplankton functional group dynamics in different periods. The study provides a valuable reference for assessing the relationship between environmental factors and phytoplankton communities, as well as for the evaluation and conservation of aquatic ecosystems in southern China's water diversion reservoirs.

Spatio-temporal dynamics of phytoplankton in a diversion reservoir and the major influencing factors: taxonomic versus functional groups classification.

Identifying factors affecting phytoplankton dynamics is crucial to the management of aquatic ecosystems. A lot of scholars have conducted intensive studies on phytoplankton in lake or reservoirs, but not many studies have been conducted on diversion reservoirs. To explore the seasonal and spatial variation of phytoplankton communities and their relationship with environmental factors in the context of water diversion, a case study was carried out at XiKeng (XK) reservoir in South China. In this study, month-by-month water samples and phytoplankton were collected from this reservoir from December, 2021, to July, 2022. The results showed that the phytoplankton community was characterized by significant spatial and temporal variations. There were significant differences in phytoplankton abundance and structure in the reservoirs in terms of time. The abundance of phytoplankton cells and the proportion of Cyanobacteria in the reservoir showed a trend of increasing from autumn to spring and then decreasing from spring to summer, while the functional group evolved from S1 in autumn to SN in spring and summer. The abundance of phytoplankton was influenced by the dynamic water division and the characteristics of the reservoir itself, resulting in a spatial distribution characteristic of AIII > AII > AI. Water temperature (WT) and nutrients were the key factors driving the changes in phytoplankton abundance and community structure in the reservoir. These findings will deepen our understanding of the spatial and temporal dynamics of phytoplankton community structure in diversion reservoirs and provide a basis for freshwater water ecological management strategies.

Visualizing Oceanographic Data to Depict Long-term Changes in Phytoplankton.

Oceanographic time series providean important perspective on environmental processes in ecosystems. The Narragansett Bay Long-Term Plankton Time Series (NBPTS) in Narragansett Bay, Rhode Island, USA, represents one of the longest plankton time series (1959-present) of its kind in the world and presents a unique opportunity to visualize long-term change within an aquatic ecosystem. Phytoplankton representthe base of the food web in most marine systems, including Narragansett Bay. Therefore, communicating their importance to the 2.4 billion people who live within the coastal ocean is critical. We developed a protocol with the goal of visualizing the diversity and magnitude of phytoplankton by utilizing Adobe Illustrator to convert microscopic images of phytoplankton collected from the NBPTS into vector graphics that could be conformed into repetitive visual patterns through time. Numerically abundant taxa or those that posed economic and health threats, such as the harmful algal bloom taxa, Pseudo-nitzschia spp., were selected for image conversion. Patterns of various phytoplankton images were then created based on their relative abundance for select decades of data collected (1970s, 1990s, and 2010s). Decadal patterns of phytoplankton biomass informed the outline of each decade while a background color gradient from blue to red was used to reveal a long-term temperature increase observed in Narragansett Bay. Finally, large, 96-inch by 34-inch panels were printed with repeating phytoplankton patterns to illustrate potential changes in phytoplankton abundance over time. This project enables visualization of literal shifts in phytoplankton biomass, that are typically invisible to the naked eye while leveraging real-time series data (e.g., phytoplankton biomass and abundance) within the art piece itself. It represents an approach that can be utilized for many other plankton time series for data visualization, communication, education, and outreach efforts.

Evaluation of the response of phytoplankton communities to heavy metal stresses using multi-statistical approaches, Alexandria coast, Egypt

This is the first study to investigate the antioxidant response of the phytoplankton community to heavy metal stress in the open sea. The levels of Cu, Zn, Cd, Mn, Pb, and Fe were determined in the phytoplankton community and water in Abu Talat (AT), and El Dekhella Harbour (DH), Alexandria coast during spring 2018 and autumn 2019. Furthermore, the changes in phytoplankton abundance, the bioconcentration factor (BCF), the metal pollution index (MPI), and the pollution load index (PLI) were used to assess pollution status. The phytoplankton density in the DH stations was 17–42 folds higher than in the AT. The order of BCF during spring was Fe > Zn > Pb > Cu > Mn > Cd. However, Fe > Zn > Mn > Cu > Pb > Cd was found in both areas during the autumn. The BCF, MPI, and PLI of the phytoplankton community revealed that DH is more polluted than AT. The phenol, 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity and total antioxidant activity of the phytoplankton communities achieved higher values in DH than in AT stations, in response to heavy metal stresses. Principal component analysis was performed to follow pollution sources, suggesting that station 3 in both seasons was a hot spot because of stagnant water. A correlation matrix indicated that phenol and DPPH interacted positively in both locations during the two seasons. Analysis of variances with replicate tests on heavy metals in phytoplankton revealed significant seasonal differences across the two areas at a significance level < 0.05.

Analysis of phytoplankton abundance in kassikebo waters, pangkep regency, south sulawesi, indonesia

Changes in nutrient concentrations can be caused by anthropogenic activities in coastal and marine waters. This affects the abundance of phytoplankton. The waters experiencing it are the waters of Kassikebo Pangkep, South Sulawesi, Indonesia. For this reason, research has been carried out to analyze the abundance and structure of phytoplankton communities in these waters, from January to July 2022. To identify phytoplankton, 100 L of seawater samples were filtered, which were taken at each station. The results of that water filter, identified in the laboratory. The results showed that the classes of phytoplankton found were Bacillariophyceae and Cyanophyceae. Species found such as Skeletonema and Detonula. The results of One-way ANOVA showed that phytoplankton abundance was not significantly different between observation stations (p&gt;0.05). Changes in phytoplankton abundance are caused by pH.

Assessment of Phytoplankton Diversity in Downstream Region of Meenachil River,kerala, During the Pre-monsoon and Monsoon Season

The present study aimed to assess the Phytoplankton diversity in the downstream of Meenachil River ,Kerala,during pre-monsoon and monsoon seasons. A total of 39 species belonging to five taxonomic divisions were identified, namely Chlorophyceae, Bacillariophyceae, Cyanophyceae, Euglenophyceae, and Xanthophyceae. The results revealed that Chlorophyceae was the dominant group, followed by Bacillariophyceae, Cyanophyceae, Euglenophyceae, and Xanthophyceae. The season-wise distribution of phytoplankton showed a higher abundance in the pre-monsoon season compared to the monsoon season. This study provides valuable insights into the phytoplankton diversity of Meenachil River, Kerala, and highlights the significance of monitoring seasonal changes in phytoplankton abundance for effective water resource management. The findings of this study can be useful for further research on water quality monitoring and management in rivers

Multidecadal changes in biology influence the variability of the North Atlantic carbon sink

The North Atlantic Ocean is the most intense marine sink for anthropogenic carbon dioxide (CO2) in the world’s oceans, showing high variability and substantial changes over recent decades. However, the contribution of biology to the variability and trend of this sink is poorly understood. Here we use in situ plankton measurements, alongside observation-based sea surface CO2 data from 1982 to 2020, to investigate the biological influence on the CO2 sink. Our results demonstrate that long term variability in the CO2 sink in the North Atlantic is associated with changes in phytoplankton abundance and community structure. These data show that within the subpolar regions of the North Atlantic, phytoplankton biomass is increasing, while a decrease is observed in the subtropics, which supports model predictions of climate-driven changes in productivity. These biomass trends are synchronous with increasing temperature, changes in mixing and an increasing uptake of atmospheric CO2 in the subpolar North Atlantic. Our results highlight that phytoplankton play a significant role in the variability as well as the trends of the CO2 uptake from the atmosphere over recent decades.

Response of the bacterioplankton composition to inorganic nutrient loading and phytoplankton in southern Korean coastal waters: A mesocosm study

AbstractIn Korean coastal waters (KCW), nutrient loading from the four major rivers usually peaks in summer, probably due to the large amount of water discharge in rainy seasons, but little is known about the responses of the bacterial community composition to inorganic nutrient loading. To gain deeper understanding of variations in marine microbial biodiversity and function with inorganic nutrient loading, a large‐scale mesocosm (1,000 L) experiment was conducted in southern KCW for 10 days in summer (July 27 through August 6, 2015) and the bacterioplankton community composition (BCC) was investigated using 16S rRNA amplicon pyrosequencing method. The bioassays established in the mesocosm were designed with the following each nutrient dosing treatments: nitrate (+N), phosphate (+P), and nitrate plus phosphate (+NP). Among the three treatments, the +NP and +N treatments exhibited the largest and second‐largest increases in phytoplankton abundance, respectively, whereas there was relatively less variation under the +P treatment. Enhanced growth of phytoplankton not only induced increases in pH and bacterial abundance (p &lt; .05) but also led to changes in the BCC: the orders Flavobacteria, Micrococcales, Oceanospirillales, and Rhodobacterales exhibited increases in relative abundance, whereas Methylophilales, Puniceicoccales, SAR11, SAR116, and SAR86 showed a decreasing trend. Inorganic nutrients may directly contribute to variation in the BCC, as the relative abundance of Sphingobacteriales, containing members that undergo chemotaxis toward inorganic nutrients, was increased by the +N treatment. Given that these findings, changes in phytoplankton abundance due to nutrient addition may be the most crucial component resulting in variation in the BCC.

A review of past and present summer primary production processes in the Ross Sea in relation to changing ecosystems

We analyse primary production processes during austral summer 1996 and 2001 in different environmental conditions such as ice-free waters and extensive ice-covered areas. Spatio-temporal distribution of phytoplankton biomass and functional groups along with photosynthetic parameters are presented. Production vs irradiance (P vs E) experiments were performed using 14 C incubations at several stations and three or four different depths to define the eco-physiology of phytoplankton communities.The results of the oceanographic campaign conducted in ice-free waters of the Ross Sea (summer 1996) emphasize that these ecosystems are characterized by high nutrient low chlorophyll (HNLC) conditions due to limiting factors (eg Fe). Conversely, the results of the oceanographic cruise in extensively packice-covered areas (summer 2001) indicate that the average phytoplankton biomass (estimated from Chl a ) was about three times the values recorded in ice-free conditions, but the primary production was relatively lower. In fact, in situ primary production and P vs E experiments over few days show that high primary production values occurred in most of the area, but only within the first five meters of the water column and the melting pack ice. Notwithstanding some high values of phytoplankton biomass during the 2001 campaign, water column stability, similar irradiance levels along the water column, photosynthetic capacity was suppressed in deeper layers, indicating a low carrying capacity of the pelagic ecosystem due to iron limitation, as shown by low values of the photo-chemical efficiency of photosystem II (PSII), variable fluorescence and maximal fluorescence ratio (Fv/Fm). In contrast with a very high variability in phytoplankton biomass at several temporal and spatial scales, photosynthetic parameters (P B max , a, E k ) varied within narrow ranges. Relevant changes in phytoplankton abundance and species composition are reported in this study although the environmental factors that drive these changes in primary production processes and prevalence of principal functional groups of phytoplankton communities compared to the past (1996 and 2001) are still unknown. The effect of these changes on the carrying capacity of Ross Sea ecosystems, carbon export and the potentially new asset of the food web will need to be determined.

Historical trends and future distribution of anchovy spawning in the Bay of Biscay

Future scenarios of fish stocks and the impacts of climate variability and change on fisheries are critical to anticipate and minimize potential economic losses in this sector. In this study, we assessed the impact of recent sea warming and future climate change on anchovy in the Bay of Biscay, where sea surface temperature has increased in the last three decades. We analyzed the historical evolution of the anchovy spawning and built species distribution models that are projected under the RCP8.5 climate change scenario. The historical analysis of anchovy spawning showed that spawning peak advanced at a rate of 5.5 days/decade from 1987 to 2015, and the gonadosomatic index (as proxy of spawning activity) generally increased, which might be associated to changes in phytoplankton abundance. In addition, the spawning area expanded and contracted depending on the total egg production. In the future, the overall anchovy egg abundance in the Bay of Biscay is expected to increase between 1.05 and 2.66-fold under the RCP8.5 climate change scenario by the mid and end-of-the-21st-century, respectively. Projected environmental changes are expected to induce an expansion of the spawning area (7.8% and 16.4% for mid- and end-of-the-century) and higher egg densities.

Seasonal Shifts in Bacterial Community Responses to Phytoplankton-Derived Dissolved Organic Matter in the Western Antarctic Peninsula.

Bacterial consumption of dissolved organic matter (DOM) drives much of the movement of carbon through the oceanic food web and the global carbon cycle. Understanding complex interactions between bacteria and marine DOM remains an important challenge. We tested the hypothesis that bacterial growth and community succession would respond differently to DOM additions due to seasonal changes in phytoplankton abundance in the environment. Four mesocosm experiments were conducted that spanned the spring transitional period (August–December 2013) in surface waters of the Western Antarctic Peninsula (WAP). Each mesocosm consisted of nearshore surface seawater (50 L) incubated in the laboratory for 10 days. The addition of DOM, in the form of cell-free exudates extracted from Thalassiosira weissflogii diatom cultures led to changes in bacterial abundance, production, and community composition. The timing of each mesocosm experiment (i.e., late winter vs. late spring) influenced the magnitude and direction of bacterial changes. For example, the same DOM treatment applied at different times during the season resulted in different levels of bacterial production and different bacterial community composition. There was a mid-season shift from Collwelliaceae to Polaribacter having the greatest relative abundance after incubation. This shift corresponded to a modest but significant increase in the initial relative abundance of Polaribacter in the nearshore seawater used to set up experiments. This finding supports a new hypothesis that starting community composition, through priority effects, influenced the trajectory of community succession in response to DOM addition. As strong inter-annual variability and long-term climate change may shift the timing of WAP phytoplankton blooms, and the corresponding production of DOM exudates, this study suggests a mechanism by which different seasonal successional patterns in bacterial communities could occur.

A river‐scale Lagrangian experiment examining controls on phytoplankton dynamics in the presence and absence of treated wastewater effluent high in ammonium

AbstractPhytoplankton are critical component of the food web in most large rivers and estuaries, and thus identifying dominant controls on phytoplankton abundance and species composition is important to scientists, managers, and policymakers. Recent studies from a variety of systems indicate that ammonium ( ) in treated wastewater effluent decreases primary production and alters phytoplankton species composition. However, these findings are based mainly on laboratory and enclosure studies, which may not adequately represent natural systems. To test effects of effluent high in ammonium on phytoplankton at the ecosystem scale, we conducted whole‐river–scale experiments by halting discharges to the Sacramento River from the regional wastewater treatment plant (WWTP), and used a Lagrangian approach to compare changes in phytoplankton abundance and species composition in the presence (+EFF) and absence (−EFF) of effluent. Over 5 d of downstream travel from 20 km above to 50 km below the WWTP, chlorophyll concentrations declined from 15–25 to ∼2.5 μg L−1, irrespective of effluent addition. Benthic diatoms were dominant in most samples. We found no significant difference in phytoplankton abundance or species composition between +EFF and −EFF conditions. Moreover, greatest declines in chlorophyll occurred upstream of the WWTP where concentrations were low. Grazing by clams and zooplankton could not account for observed losses, suggesting other factors such as hydrodynamics and light limitation were responsible for phytoplankton declines. These results highlight the advantages of conducting ecosystem‐scale, Lagrangian‐based experiments to understand the dynamic and complex interplay between physical, chemical, and biological factors that control phytoplankton populations.

Bi-weekly Changes in Phytoplankton Abundance in 25 Tributaries of Lake St. Francis, Canada: Evaluating the Occurrence of Nuisance and Harmful Algae

Abstract Eutrophication and undesirable algae growth remain listed as beneficial use impairments in 14 Great Lakes areas of concern, including the Cornwall/St. Lawrence region. However, there is currently a lack of information regarding the distribution and frequency of undesirable algae occurrences, particularly in lotic systems influencing this region. Here, we examine phytoplankton assemblages in 25 tributaries of Lake St. Francis (St. Lawrence River) between the months of May and September (2013 and 2014) in order to evaluate abundance and taxonomic composition. Phytoplankton in the tributaries were dominated by diatoms, followed by chlorophytes, and on average only ~ 1% of overall composition were cyanobacteria. The low proportion of chlorophytes and cyanobacteria was surprising, given that these tributaries are located in watersheds dominated by agricultural activities. Stream order was not related to total phytoplankton abundance, potentially due to the highly disturbed nature of the catchments. Multiple linear regression models were developed to better understand possible chemical and physical factors contributing to phytoplankton abundance and cyanobacteria occurrence across all sites. Water temperature, total phosphorus and day of year were identified as the best predictors of phytoplankton abundance, and water temperature and depth were identified as predictors for cyanobacteria occurrence. While these models were significant, they only accounted for a low amount of the variability (between 8 and 12%) of total phytoplankton and cyanobacteria abundance. Year-to-year variation between mean phytoplankton abundances was also high, which was reflected in the low correlation between the rank order of sites between 2013 and 2014 (ρ = 0.16).

Spatio-temporal patterns in phytoplankton assemblages in inshore–offshore gradients using flow cytometry: A case study in the eastern English Channel

A pulse-shape recording flow cytometer (CytoSense©) was applied to the monitoring of changes in phytoplankton distribution along an inshore–offshore transect across the eastern English Channel (EEC), on 13 occasions during the main productive period of the year. Amongst the eight phytoplankton groups discriminated, picophytoplankton (picoeukaryotes and Synechococcus spp.) and Phaeocystis globosa nanoflagellates were the main contributors to total phytoplankton abundance, while Diatoms-like, Coccolithophores, and Cryptophytes represented each one less than 5%. High spatial resolution revealed important changes on relatively short distances. Moreover, a general decrease of Diatoms-like, P. globosa haploid cells, Coccolithophores, and picoeukaryote abundance was evidenced from inshore to offshore waters, associated with an increase of Synechococcus spp. abundance. Seasonal variability accounted for 71% of phytoplankton abundance changes. Compared to previous studies in the area the CytoSense allowed highlighting new players during the winter–spring–summer phytoplankton succession: (i) high abundance of Synechococcus spp. and picoeukaryotes I in winter and of Synechococcus spp. also in the summer, (ii) a transient abundance peak of picoeukaryotes II, and (iii) high abundance of Coccolithophores and Cryptophytes during the wax of P. globosa bloom and in the summer. The relationships between environmental variables and phytoplankton assemblages indicated that nutrients and the daily light intensity were the most important parameters in structuring the winter–spring–summer transitions.

Seasonal Changes in Mycosporine-Like Amino Acid Production Rate with Respect to Natural Phytoplankton Species Composition.

After in situ incubation at the site for a year, phytoplanktons in surface water were exposed to natural light in temperate lakes (every month); thereafter, the net production rate of photoprotective compounds (mycosporine-like amino acids, MAAs) was calculated using 13C labeled tracer. This is the first report describing seasonal variation in the net production rate of individual MAAs in temperate lakes using a compound-specific stable isotope method. In the mid-latitude region of the Korean Peninsula, UV radiation (UVR) usually peaks from July to August. In Lake Paldang and Lake Cheongpyeong, diatoms dominated among the phytoplankton throughout the year. The relative abundance of Cyanophyceae (Anabaena spiroides) reached over 80% during July in Lake Cheongpyeong. Changes in phytoplankton abundance indicate that the phytoplankton community structure is influenced by seasonal changes in the net production rate and concentration of MAAs. Notably, particulate organic matter (POM) showed a remarkable change based on the UV intensity occurring during that period; this was because of the fact that cyanobacteria that are highly sensitive to UV irradiance dominated the community. POM cultured in Lake Paldang had the greatest shinorine (SH) production rate during October, i.e., 83.83 ± 10.47 fgC·L−1·h−1. The dominance of diatoms indicated that they had a long-term response to UVR. Evaluation of POM cultured in Lake Cheongpyeong revealed that there was an increase in the net MAA production in July (when UVR reached the maximum); a substantial amount of SH, i.e., 17.62 ± 18.34 fgC·L−1·h−1, was recorded during this period. Our results demonstrate that both the net production rate as well as the concentration of MAAs related to photoinduction depended on the phytoplankton community structure. In addition, seasonal changes in UVR also influenced the quantity and production of MAAs in phytoplanktons (especially Cyanophyceae).

A latitudinally banded phytoplankton response to 21st century climate change in the Southern Ocean across the CMIP5 model suite

Abstract. Changes in Southern Ocean (SO) phytoplankton distributions with future warming have the potential to significantly alter nutrient and carbon cycles as well as higher trophic level productivity both locally and throughout the global ocean. Here we investigate the response of SO phytoplankton productivity and biomass to 21st century climate change across the CMIP5 Earth System Model suite. The models predict a zonally banded pattern of phytoplankton abundance and production changes within four regions: the subtropical (~ 30 to 40° S), transitional (~ 40 to 50° S), subpolar (~ 50 to 65° S) and Antarctic (south of ~ 65° S) bands. We find that shifts in bottom-up variables (nitrate, iron and light availability) drive changes in phytoplankton abundance and production on not only interannual, but also decadal and 100-year timescales – the timescales most relevant to climate change. Spatial patterns in the modelled mechanisms driving these biomass trends qualitatively agree with recent observations, though longer-term records are needed to separate the effects of climate change from those of interannual variability. Because much past observational work has focused on understanding the effects of the Southern Annular Mode (SAM) on biology, future work should attempt to quantify the precise influence of an increasingly positive SAM on SO biology within the CMIP5 models. Continued long-term in situ and satellite measurements of SO biology are clearly needed to confirm model findings.

Phytoplankton Abundance Constrains Planktonic Energy Subsidy to Benthic Food Web

Linkages across habitats between habitats are fundamental components of ecological processes. As a major characteristic of within-lake food webs, linkage of benthic and planktonic food webs has received a great deal of attention in recent aquatic studies. However, planktonic energy subsidy to benthic consumers has been infrequently tested in experiment. In a field experiment manipulating nutrients and phytoplankton abundance, we ask how changes in phytoplankton abundance affect planktonic energy subsidy to benthic primary consumers across nutrient levels. Our results suggest that the planktonic subsidy to benthic primary consumers depends on the phytoplankton abundance. Furthermore, highly taxon-specific planktonic energy subsidy to benthic primary consumers suggests that the benthic community composition partially determines the degree of the planktonic-benthic linkage. Because shallow and eutrophic lakes distribute worldwide, and many ecological functions are mediated by planktonic-benthic linkage, it will be important to consider these findings to protection and restoration of lake ecosystems.

Historical variability in past phytoplankton abundance and composition in Doubtful Sound, New Zealand

Doubtful Sound, New Zealand, provides an exceptional opportunity to study a ‘baseline’ coastal ecosystem with an intact watershed. We present the first data on historical changes in phytoplankton abundance and community composition for three sites in Doubtful Sound using sediment records. Profiles of sedimentary concentrations of β-carotene (a proxy of total algal abundance, 0.021–1.345mmolg organic carbon−1) and carotenoids were generally depleted, indicating low autochthonous production. Phytoplankton pigments and diatom frustules in Doubtful Sound indicate that diatoms have been prevalent for at least the last ca. 350 years; however, the relative importance of marine and freshwater diatoms has varied through time. Further, the timing of change in phytoplankton biomass and community composition differed among the sites within Doubtful Sound. This finding highlights the need to use multiple sites and complementary biomarkers when studying historical changes in phytoplankton communities in complex ecosystems with strong physicochemical gradients such as fjords.

Implications of seasonal mixing for phytoplankton production and bloom development

Based on a 1D model considering phytoplankton and nutrients in a vertical water column, we investigate the consequences of temporal and spatial variations in turbulent mixing for phytoplankton production and biomass. We show that in seasonally mixed systems, the processes controlling phytoplankton production and the sensitivity of phytoplankton abundance to ambient light, trophic state and mixed-layer depth differ substantially from those at steady state in systems with time-constant diffusivities. In seasonally mixed systems, the annually replenished nutrient pool in the euphotic zone is an important factor for phytoplankton production supporting bloom development, whereas without winter mixing, production mainly depends on the diffusive nutrient flux during stratified conditions. Seasonal changes in water column production are predominantly determined by seasonal changes in phytoplankton abundance, but also by seasonal changes in specific production resulting from the transport of nutrients, the exploitation of the nutrient pool and the increase in light shading associated with phytoplankton growth. The interplay between seasonal mixing and the vertical distribution of mixing intensities is a key factor determining the relative importance of the processes controlling phytoplankton production and the sensitivity of the size and timing of the annual maximum phytoplankton abundance to the abiotic conditions.

Inter-annual abundance variation in some genera of diatom and zooplankton in a mangrove ecosystem

This study presents data for the abundance of phytoplankton and zooplankton and related habitat parameters for Lothian Island mangrove ecosystem located at the coastal boundary of the Ganges River delta. Over the 3 study years, total abundance of phytoplankton and zooplankton was lowest during the monsoon period. In 2008, the most common diatom genera (by % relative abundance) were Skeletonema cf. costatum (14.2), Thalassiothrix (9.36), Nitzschia sigma (8.16), Coscinodiscus radiatus (7.65), Chaetoceros (6.64), Pleurosigma (3.05), Thalassionema (1.77), Ditylum brightwellii (1.71), and Cyclotella (1.0), whereas in 2010 they were Skeletonema cf. costatum (41.7), Chaetoceros (11.1), Thalassiothrix (6.04), Nitzschia sigma (4.49), Coscinodiscus radiatus (3.96), Cyclotella (2.61), Thalassionema (2.11), Pleurosigma (1.22) and, Ditylum brightwellii (1.01). Relative abundance of the zooplankton size classes typically followed the order meso > micro > macro and Copepods were the most abundant taxa (54.6 % of total zooplankton abundance). Total abundance of both phyto and zooplankton almost doubled in 2010 relative to 2008 although the ratio of the two remained constant (Zooplankton: phytoplankton = 0.002). The N:P ratio of water did not change much over the study and did not seem to be responsible for phytoplankton abundance changes; rather interannual variations in phytoplankton abundance could be explained by a simple predator–prey-relationship with zooplankton.