Plankton Dynamics Research Articles

Cobalamin and microbial plankton dynamics along a coastal to offshore transect in the Eastern North Atlantic Ocean.

Cobalamin (B12) is an essential cofactor that is exclusively synthesized by some prokaryotes while many prokaryotes and eukaryotes require an external supply of B12. The spatial and temporal availability of B12 is poorly understood in marine ecosystems. Field measurements of B12 along with a large set of ancillary biotic and abiotic factors were obtained during three oceanographic cruises in the NW Iberian Peninsula, covering different spatial and temporal scales. B12 concentrations were remarkably low (<1.5 pM) in all samples, being significantly higher at the subsurface Eastern North Atlantic Central Water than at shallower depths, suggesting that B12 supply in this water mass is greater than demand. Multiple regression models excluded B12 concentration as predictive variable for phytoplankton biomass or production, regardless of the presence of B12-requiring algae. Prokaryote production was the best predictor for primary production, and eukaryote community composition was better correlated with prokaryote community composition than with nutritional resources, suggesting that biotic interactions play a significant role in regulating microbial communities. Interestingly, co-occurrence network analyses based on 16S and 18S rRNA sequences allowed the identification of significant associations between potential B12 producers and consumers (e.g. Thaumarchaeota and Dynophyceae, or Amylibacter and Ostreococcus respectively), which can now be investigated using model systems in the laboratory.

Impact of El Niño-Southern Oscillation on plankton ciliates from a saline lowland river in South America

We analyzed the structure and dynamics of plankton ciliates from the Salado River, Buenos Aires (Argentina), during El Niño-Southern Oscillation events, to evaluate their response to alterations of certain environmental variables during these climatic phenomena. The basin exhibits intense land use at the headwaters and fluctuating salinity along the main channel, canals and tributaries. During El Niño (1997-1998), heavy rainfall caused high discharge, and low mean conductivity values were recorded along with low mean abundances in the entire basin. During neutral (2004-2005) and La Niña (2007-2009) events, the discharge was reduced, and mean conductivity was double the values recorded during El Niño, with maxima of mean abundances and diversity at the headwaters and the lower basin. The most abundant ciliates were tintinnids, heterotrichs and peritrichs. Species replacement was detected along the river system, mainly during the neutral event. At the headwaters and canals, abundance peaks of certain species were attributed to the strong human impact (nutrients and sewage inputs) and increased salinity, allowing the establishment of euryhaline ciliates. In the middle basin, freshwater species predominated, although less abundantly due to higher water flow. The mouth sector showed abundance peaks of an estuarine tintinnid. Temperature, conductivity and suspended solids were the most important variables driving ciliate structure. High discharge as a result of heavy rainfall during El Niño negatively influenced ciliate assemblages. In contrast, low water conditions during the other events allowed the development of diverse assemblages, increasing species number and abundance of particular species.

A metabarcoding comparison of taxonomic richness and composition between the water column and the benthic boundary layer

Abstract Zooplankton monitoring in shelf seas predominantly uses nets that miss the benthic boundary layer (BBL) just above the seabed. However, this boundary between pelagic and benthic assemblages can be faunistically rich, having its own distinct hyperbenthic fauna and acting as a low-light refuge for overwintering or dielly migrating zooplankton. To compare species richness and composition between pelagic and BBL habitats, we sampled a long-term monitoring site in the Western English Channel seasonally. Metabarcoding methods applied to vertical net samples (top 50 m in a ∼54-m water column) and those from a hyperbenthic sledge generated &amp;gt;100 000 sequences clustered into 294 operational taxonomic units. Of these, 215 were found in the BBL and 170 in the water column. Some key taxa (e.g. mysids) were native to the BBL; by contrast, other delicate taxa (e.g. ctenophores) seemed to avoid the BBL. The major contrasts in plankton composition related to the seasonal cycle rather than to pelagic-BBL differences, suggesting that the basic dynamics of the site are captured by our ongoing long-term weekly resolution monitoring. Overall, metabarcoding approaches, applied to both water column and BBL, provide an independent view of plankton dynamics, and augment existing traditional methods.

An investigation of delay induced stability transition in nutrient-plankton systems

Abstract In this paper, a nutrient-plankton interaction model is proposed to explore the characteristic of plankton system in the presence of toxic phytoplankton and discrete time delay. Anti-predator efforts of phytoplankton by toxin liberation act as a prominent role on plankton dynamics. Toxicity controls the system dynamics and reduces the grazing rate of zooplankton. The toxic substance released by phytoplankton is not an instantaneous process, it requires some time for maturity. So, a discrete time delay is incorporated in the toxin liberation by the phytoplankton. The choice of functional response is important to understand the toxin liberation and it depends on the nonlinearity of the system, which follows the Monod-Haldane type functional response. Theoretically, we have studied the boundedness condition along with all the feasible equilibria analysis and stability criteria of delay free system. We have explored the local stability conditions of delayed system. The existence criterion for stability and direction of Hopf-bifurcation are also derived by using the theory of normal form and center manifold arguments. The essential features of time delay are studied by time series, phase portrait and bifurcation diagram. We perform a global sensitivity analysis to identify the important parameters of the model having a significant impact on zooplankton. Our numerical investigation reveals that the toxin liberation delay switches the stability of the system from stable to limit cycle and after a certain interval chaotic dynamics is observed. High rate of toxic substances production shows extinction of zooplankton. Further, the negative and positive impacts of other control parameters are studied. Moreover, to support the occurrence of chaos, the Poincare map is drawn and the maximum Lyapunov exponents are also computed.

Ecological impacts of freshwater algal blooms on water quality, plankton biodiversity, structure, and ecosystem functioning

Harmful algal blooms are among the emerging threats to freshwater biodiversity that need to be studied further in the Anthropocene. Here, we studied freshwater plankton communities in ten tropical reservoirs to record the impact of algal blooms, comprising different phytoplankton taxa, on water quality, plankton biodiversity, and ecosystem functioning. We compared water quality parameters (water transparency, mixing depth, pH, electrical conductivity, dissolved inorganic nitrogen, total dissolved phosphorus, total phosphorus, chlorophyll-a, and trophic state), plankton structure (composition and biomass), biodiversity (species richness, diversity, and evenness), and ecosystem functioning (phytoplankton:phosphorus and zooplankton:phytoplankton ratios as a metric of resource use efficiency) through univariate and multivariate analysis of variance, and generalized additive mixed models in five different bloom categories. Most of the bloom events were composed of Cyanobacteria, followed by Dinophyta and Chlorophyta. Mixed blooms were composed of Cyanobacteria plus Bacillariophyta, Chlorophyta, and/or Dinophyta, while non-bloom communities presented phytoplankton biomass below the threshold for bloom development (10 mg L−1, WHO alert level 2). Higher phytoplankton biomasses were recorded during Cyanobacteria blooms (15.87–273.82 mg L−1) followed by Dinophyta blooms (18.86–196.41 mg L−1). An intense deterioration of water quality, including higher pH, eutrophication, stratification, and lower water transparency, was verified during Cyanobacteria and mixed blooms, while Chlorophyta and Dinophyta blooms presented lower pH, eutrophication, stratification, and higher water transparency. All bloom categories significantly impacted phytoplankton and zooplankton structure, changing the composition and dominance patterns. Bloom intensity positively influenced phytoplankton resource use efficiency (R2 = 0.25; p < 0.001), while decreased zooplankton resource acquisition (R2 = 0.51; p < 0.001). Moreover, Cyanobacteria and Chlorophyta blooms negatively impacted zooplankton species richness, while Dinophyta blooms decreased phytoplankton richness. In general, Cyanobacteria blooms presented low water quality and major threats to plankton biodiversity, and ecosystem functioning. Moreover, we demonstrated that biodiversity losses decrease ecosystem functioning, with cascading effects on plankton dynamics.

Preliminary insights on the fine-scale responses in larval Gilchristella aestuaria (Family Clupeidae) and dominant zooplankton to estuarine harmful algal blooms

Estuarine ecosystems are increasingly threatened by eutrophication. In a warm-temperate South African estuary, modified hydrodynamics and agricultural return flows drive eutrophication which has resulted in recurrent harmful algal blooms (HABs). These bloom conditions provided an opportunity to investigate the fine-scale temporal responses of the most dominant larval fish (Clupeidae: Gilchristella aestuaria) and zooplankton (Copepoda: Pseudodiaptomus hessei, Paracartia longipatella; Mysida: Mesopodopsis wooldridgei, Rhopalophthalmus terranatalis) species to HABs (Raphidophyceae: Heterosigma akashiwo). Data were collected within the mesohaline zone during spring and analysed according to HAB phases (‘bloom’, ‘decay’, ‘intermediate’). During blooms, low densities of predominantly postflexion G. aestuaria and high prey (P. hessei) and predator (R. terranatalis) densities were recorded. The density of G. aestuaria was higher during the ‘decay’ phase and consisted mainly of preflexion and newly hatched individuals. Gilchristella aestuaria dynamics were best explained by temperature, R. terranatalis density, supersaturated dissolved oxygen and bloom biomass. The HAB also resulted in a mismatch between larval G. aestuaria and its main prey, P. hessei. Recurrent HABs threaten estuarine ecosystem function by driving the loss of forage fish. This study provided insight into the fine-scale consequences that HABs have on plankton dynamics and is relevant in a future of global change where eutrophication will intensify.

Phytoplankton phenology in algerian continental shelf and slope waters using remotely sensed data

Understanding the dynamics of phytoplankton provides important information on the health and richness of a marine ecosystem. In the Mediterranean Sea, significant phytoplankton variability has been observed between the western and eastern basins and between open ocean and coastal waters. In this study, we used eleven years' (2003–2013) MERIS and MODIS sea surface chlorophyll-a (Chla) data to investigate the spatial and temporal variability of phytoplankton in the Algerian shelf and slope waters (ASW), in the southwestern part of the Mediterranean Sea. We assessed the inter-annual and seasonal variability of phytoplankton biomass, retrieved thirteen pixel-based phenology metrics using TIMESAT algorithms, and determined the influence of precipitation on phytoplankton dynamics. Our results reveal differences between the western and eastern parts of ASW. In the eastern part of the coast, the production season starts one month later than in the western region. It also peaks about 15 days earlier and ends one month earlier as compared to the west. As a result, the productive season is shorter in the east than in the west. The area between Béjaïa and Skikda stands out, with the highest Chla values and the highest variability. These findings show that the phytoplankton dynamics varies also at the scale of ASW in timing and magnitude, which is complementary with studies previously conducted at the Mediterranean Sea scale. Correlation analysis shows that rainfall influences phytoplankton biomass and some phenology metrics’ variability. However, other physical and biogeochemical variables should be investigated for a more complete understanding of the plankton dynamics and to assess the impact of this variability on species abundance and diversity.

Temperature-related timing of the spring bloom and match between phytoplankton and zooplankton

ABSTRACT Global warming is causing changes in the food web structure and seasonal plankton dynamics. The Baltic Sea is one of the fastest-warming sea areas and warming consequently affects the timing and magnitude of phytoplankton blooms. Based on available Chlorophyll a data from nine years between 1979 and 2018, from the entrance to the Gulf of Finland, we studied the timing of the phytoplankton spring bloom in relation to spring seawater temperature. We found the peak of the bloom to occur earlier in years with higher spring seawater temperature. In warmer years, there was also a shorter time lag between phytoplankton and zooplankton biomass peaks. In addition, it seems as the spring bloom total biomass has decreased with time, with more extensive summer blooms during later years, in line with the general trend observed in the Baltic Sea. The spring bloom has traditionally been considered the most important part of the season, but we argue that the whole growth season should be investigated since summer blooms appear to increase with warming.

Impact of awareness on environmental toxins affecting plankton dynamics: a mathematical implication

The widespread problem of water pollution due to enhanced concentration of anthropogenic effluents is becoming a global issue. Public environmental awareness may be a plausible factor for the control of toxicants in the aquatic medium. The present paper is devoted to study the impact of awareness among human on reduction of environmental toxins affecting planktonic system. The provision of awareness among people helps to maintain the ecological balance of the system by reducing the input rate of toxicants through anthropogenic sources. The conditions for existence and local asymptotic stability of all feasible steady states of the system are derived. Our study reveals that the system is stable for low or high input rate of toxicants, but for intermediate ranges, the system produces oscillations by destroying the stable dynamics. Moreover, for very large level of pollutants, zooplankton disappears from the system. Importantly, the limited supply of additional food to zooplankton prevents the crash of aquatic food web system. Sensitivity results evoke that environmental toxins can be reduced to a low level by imparting awareness among human, thereby maintaining the rhythm of the planktonic ecosystem.

Ocean Biogeochemistry in GFDL's Earth System Model 4.1 and Its Response to Increasing Atmospheric CO2

AbstractThis contribution describes the ocean biogeochemical component of the Geophysical Fluid Dynamics Laboratory's Earth System Model 4.1 (GFDL‐ESM4.1), assesses GFDL‐ESM4.1's capacity to capture observed ocean biogeochemical patterns, and documents its response to increasing atmospheric CO2. Notable differences relative to the previous generation of GFDL ESM's include enhanced resolution of plankton food web dynamics, refined particle remineralization, and a larger number of exchanges of nutrients across Earth system components. During model spin‐up, the carbon drift rapidly fell below the 10 Pg C per century equilibration criterion established by the Coupled Climate‐Carbon Cycle Model Intercomparison Project (C4MIP). Simulations robustly captured large‐scale observed nutrient distributions, plankton dynamics, and characteristics of the biological pump. The model overexpressed phosphate limitation and open ocean hypoxia in some areas but still yielded realistic surface and deep carbon system properties, including cumulative carbon uptake since preindustrial times and over the last decades that is consistent with observation‐based estimates. The model's response to the direct and radiative effects of a 200% atmospheric CO2increase from preindustrial conditions (i.e., years 101–120 of a 1% CO2yr−1simulation) included (a) a weakened, shoaling organic carbon pump leading to a 38% reduction in the sinking flux at 2,000 m; (b) a two‐thirds reduction in the calcium carbonate pump that nonetheless generated only weak calcite compensation on century time‐scales; and, in contrast to previous GFDL ESMs, (c) a moderate reduction in global net primary production that was amplified at higher trophic levels. We conclude with a discussion of model limitations and priority developments.

Multifaceted linkages among eco-physiological factors, seasonal plankton dynamics and selective feeding behavior of the green mussel (Perna viridis) in the south-east coast of the Bay of Bengal

Feeding behavior of marine bivalves is largely regulated by the interactive effects of various intrinsic biological factors and extrinsic ecological factors. Therefore, an integrated multivariate approach was applied to explore a deeper knowledge about the feeding biology of the green mussel (Perna viridis), collected from the south-east coastal regions of the Bay of Bengal in Bangladesh, by interlinking among ecological factors, seasonal plankton dynamics, reproductive traits and plankton ingestion data. The correlation test, multivariate approaches and cluster analysis displayed that both the water parameters and ingested gut plankton abundance and their compositions were predominantly influenced by the seasonality and ecological factors of the environment. The selectivity indices analysis confirmed that green mussels preferentially ingested on the selective taxa of plankton. The multivariate analyses revealed that plankton ingestion by green mussels was not discriminated by their sexual dimorphism, however, it displayed an enhancement during their gonad development and maturation stages confirming that P. viridis espouses opportunistic patterns to build up their gonads by utilizing energy from the ingested planktons available in the water column. The correlation outcomes consistently demonstrated that the quantitative ingestion of plankton was positively correlated with the gonadosomatic index value of the green mussels. Although, green mussels predominantly ingested the Coscinodiscophyceae (20–60% of total ingestion), they also selectively ingested an increased amount of Bacillariophyceae, Fragillariophyceae, Dinophyceae and zooplankton during their gonad development and maturation stages to meet the special and unique metabolic requirements of crucial gametogenesis stages. Taken together all datasets, principal component analysis (PCA) was applied: the first two principal components showed that seasonality and reproductive cycle explained >47% of the variability. In both cases, PCA analysis revealed that the multiplex scenario of selective ingestion of P. viridis on different plankton taxa were predominantly interlinked with the seasonality, ecological drivers, and plankton biomass and their community structure in the water column depending on the metabolic energy requirement during their crucial gametogenesis stages. Finally, the outcomes from these broad datasets provide a better understanding about the selective feeding behavior of P. viridis, which is essential to maintain the sustainability of the ecosystems as well as to improve the growth and productivity of the existing production systems of this important species.

Computational flow cytometry of planktonic populations for the evaluation of microbiological-control programs in district cooling plants

Biofouling poses a serious concern for the district cooling (DC) industry. Current industry practises for monitoring biofouling continue to rely on culture-based methods for microbial enumeration, which are ultimately flawed. Computational flow cytometric (cFCM) analyses, which offer enhanced reproducibility and streamlined analytics versus conventional flow cytometry were applied to samples taken from 3 sites in each of 3 plants over a 5-week sampling program. We asked whether the application of cFCM to monitoring planktonic community dynamics in DC plants could be able to provide sufficient information to enhance microbiological-control strategies at site and inform about plant performance impacts. The use of cFCM enabled the evaluation of biocide dosing, deep cleaning treatment efficiencies and routes of microbial ingress into the studied systems. Additionally, inherent risks arising from the reintroduction of microbiological communities into recently cleaned WCT basins from contaminated cooling waters were identified. However, short-term dynamics did not relate with plant performance metrics. In summary, the insights offered by this approach can inform on plant status, enable evaluations of microbial loads during biofouling mitigation programs and, ultimately, enhance industry management of the biofouling process.

Rising temperature and marine plankton community dynamics: Is warming bad?

Global warming is a major threat to the natural environment worldwide with potential adverse impact on plankton community. This will ultimately lead to a change in the dynamics of aquatic food webs. In this study we used seasonally forced multi-species version of the classic Rosenzweig–MacArthur predator–prey model to understand the role and stochastic influence of increasing temperature on marine plankton. First, stable coexistence of four phytoplankton and three zooplankton species was created in a system and then the level of temperature changed to achieve our research goal. We found that the stable coexistence of phytoplankton and zooplankton was related to periodic shifts in species biomass, variation in inter-specific competition and niche configuration. Warming significantly reduced total plankton biomass and changed turnover time of a species, with gradual warming breaking the stable coexistence of phytoplankton and zooplankton. In addition, we found that warming make specialist species more vulnerable than generalist species. After adding noise, a significant variation was observed in plankton biomass and amplification of noise was higher for phytoplankton compared to zooplankton. These results suggest that stochastic or unpredictable nature of temperature fluctuations may create a window of opportunity for the emergence of new species. Overall, warming would induce a shift in plankton dynamics and thereby exert pressure on plankton dependent communities such as fish in the long run.

Eukaryotic plankton communities across reef environments in Bocas del Toro Archipelago, Panamá

Variation in light and temperature can influence the genetic diversity and structure of marine plankton communities. While open-ocean plankton communities receive much scientific attention, little is known about how environmental variation affects plankton communities on tropical coral reefs. Here, we characterize eukaryotic plankton communities on coral reefs across the Bocas del Toro Archipelago, Panama. Temperature loggers were deployed, and midday light levels were measured to quantify environmental differences across reefs at four inshore and four offshore sites (Inshore = Punta Donato, Smithsonian Tropical Research Institute (STRI) Point, Cristobal, Punta Laurel and Offshore = Drago Mar, Bastimentos North, Bastimentos South, and Cayo de Agua). Triplicate vertical plankton tows were collected midday, and high-throughput 18S ribosomal DNA metabarcoding was leveraged to investigate the relationship between eukaryotic plankton community structure and inshore/offshore reef environments. Plankton communities from STRI Point were additionally characterized in the morning (~ 08:00), midday (~ 12:00), and late-day (~ 16:00) to quantify temporal variation within a single site. We found that inshore reefs experienced higher average seawater temperatures, while offshore sites offered higher light levels, presumably associated with reduced water turbidity on reefs further from shore. These significant environmental differences between inshore and offshore reefs corresponded with overall plankton community differences. We also found that temporal variation played a structuring role within these plankton communities, and conclude that time of community sampling is an important consideration for future studies. Follow-up studies focusing on more intensive sampling efforts across space and time, coupled with techniques that can detect more subtle genetic differences between and within communities will more fully capture plankton dynamics in this region and beyond.

The dynamics of the plankton community on Lake Siombak, a tropical tidal lake in North Sumatra, Indonesia

Abstract. Muhtadi A, Pulungan A, Nurmaiyah, Fadlhin A, Melati P, Sinaga RZ, Uliya R, Rizki M, Rohim N, Ifanda D, Leidonald R, Wahyuningsih H, Hasani Q. 2020. The dynamics of the plankton community on Lake Siombak, a tropical tidal lake in North Sumatra, Indonesia. Biodiversitas 21: 3707-3719. The tidal lake is a very dynamic estuary ecosystem and very vulnerable to environmental stresses and disturbances. Plankton is an aquatic organism that is very easily affected by environmental pressures and disturbances. This study aimed to reveal the phenomenon of plankton dynamics in tropical tidal lakes in Indonesia. The study was conducted at Siombak Lake from September 2018 to August 2019. Data were collected at high and low tides every month during the full month. The data analysis included plankton abundance, diversity index, and the relationship between water quality and plankton with PCA and succession analysis. The results showed that in Siombak Lake was found 66 genera which consisted of 54 phytoplankton genera and 12 zooplankton genera. Plankton abundance is higher in parts of the lake (stations 1-8) than in the river (stations 9-11) at both high and low tide. Temporally it shows that plankton abundance is higher in the rainy season (Feb-Aug, outside May) than in the rainy season (Sep-Jan, and May). Spatially, plankton in Siombak Lake at high tide is more influenced by TSS, phosphate, and salinity, while at low tide, it is influenced by TSS, Water transparency, BOD, silicate, salinity, and dissolved oxygen. Temporally, plankton in Siombak Lake at high tide is more influenced by salinity, conductivity, Debit, TSS, and salinity, while at low tide, it is influenced by salinity, conductivity, turbidity, TSS, TDS, DO, BOD, and COD. Based on the plankton Frontier succession graph, it shows that Siombak Lake is included in stage 1 and stage 2. Stage 1 occurs before the rainy season (August-September) and the peak of the dry season (March-April).

Bursts Characterize Coagulation of Rods in a Quiescent Fluid.

Under favorable conditions, microscopic phytoplankton cells dwelling in the oceans can divide rapidly and reach high concentrations, forming blooms that span kilometers and last for weeks. When blooms collapse, dead cells settle and aggregate into "marine snow" particles, resulting in a large and climatically important vertical flux of carbon from the ocean surface to its depth, a process known as the "biological pump." To date, the formation of marine snow has been modeled as coagulation between spherical particles driven by gravitational settling and turbulent mixing, characterized by coagulation dynamics that converge onto time-independent concentrations of aggregates. However, many phytoplankton species are elongated and how their rodlike shape affects the aggregation process has remained unknown. Here, we study marine snow formation in a quiescent fluid assuming the constituent particles are elongated and form bundles upon encounter. We derive the collision kernel between dissimilar rods settling under gravity and discover that the most frequent collisions occur between the thinnest and thickest bundles, rather than between bundles of similar size. As a consequence, in the full coagulation model that combines exponential growth with settling, the thin-thick coupling can lead to statistically stationary states where the concentrations of aggregates of different size oscillate in time, exhibiting periodic bursts. The bursts are predicted to occur on the scale of a week and eventually lead to broadening of aggregate size spectra and may thus be highly relevant for plankton dynamics and the carbon cycle in the ocean.

Complex dynamics of delay-induced plankton–fish interaction exhibiting defense

In this paper, we propose a delayed plankton–fish model with Monod–Haldane-type functional response. Many prey organisms have developed defense mechanisms against predation. Predators also exhibit ways of coping with variable environmental conditions that enter in adaptation in the event of a shortage of prey. We assume prey and middle predators exhibit defense ability towards their predators. Time delay is incorporated in middle predator as an adaptation to cope with variable environmental conditions. Analytically, we study the feasibility and boundedness of the model system by comparison principle followed by local and global stability conditions. We also investigate the stability and direction of bifurcating periodic solution by normal form theory and center manifold arguments. Numerically, we study the effect of defense and time delay on the stability behavior of the system. Our numerical results reveal that the increase in time delay system becomes unstable as well as stable under different parametric restrictions. We observe that due to defense ability in prey and middle predator system shows extinction in top predator.

Particles, protists, and zooplankton in glacier-influenced coastal Svalbard waters

Glacier retreat is an eminent consequence of exacerbating climate change. In the Svalbard archipelago, most of the glaciers are discharging fresh and turbid waters directly to the sea, substantially impacting the coastal Arctic marine ecosystems. This study attempted to characterise the environmental conditions (hydrography, turbidity, marine aggregates) in the glacial-influenced waters and relate them to the abundance and species composition of protists and zooplankton. The study was conducted in the summer of 2016 in two Svalbard fjords (Wijdefjorden and Rijpfjorden) as well as in coastal waters close to glacier terminations on two islands (Nordaustlandet and Edgeøya). Well-recognised gradients in seawater salinity, turbidity, and particle aggregates that spread from glacier fronts towards open waters were not directly associated with the corresponding horizontal gradients in plankton communities. However, the studied environmental parameters explained the high overall variability in protists and zooplankton abundance (70 and 62% of explained variation, respectively). Different vertical distribution patterns and composition of plankton and marine aggregates were observed between fjords compared to open sea island locations suggesting different origin and transport of pelagic organisms and aggregate suspensions among study locations. The results do not support the hypothesis of synchronised horizontal change in environmental and biological components, which indicates that the relation between glacier meltwaters and plankton dynamics is a derivative of complex interactions driven by several physical and ecological processes that occur at different spatiotemporal scales. Nevertheless, this investigation provides new data pertaining to particle and plankton concentrations and structure in coastal waters near glaciers, which is essential for further understanding of the future coastal Arctic ecosystems functioning under rapid glacier retreat caused by climate change.

Rapid succession drives spring community dynamics of small protists at Helgoland Roads, North Sea.

The dynamics of diatoms and dinoflagellates have been monitored for many decades at the Helgoland Roads Long-Term Ecological Research site and are relatively well understood. In contrast, small-sized eukaryotic microbes and their community changes are still much more elusive, mainly due to their small size and uniform morphology, which makes them difficult to identify microscopically. By using next-generation sequencing, we wanted to shed light on the Helgoland planktonic community dynamics, including nano- and picoplankton, during a spring bloom. We took samples from March to May 2016 and sequenced the V4 region of the 18S rDNA. Our results showed that mixotrophic and heterotrophic taxa were more abundant than autotrophic diatoms. Dinoflagellates dominated the sequence assemblage, and several small-sized eukaryotic microbes like Haptophyta, Choanoflagellata, Marine Stramenopiles and Syndiniales were identified. A diverse background community including taxa from all size classes was present during the whole sampling period. Five phases with several communities were distinguished. The fastest changes in community composition took place in phase 3, while the communities from phases 1 to 5 were more similar to each other despite contrasting environmental conditions. Synergy effects of next-generation sequencing and traditional methods may be exploited in future long-term observations.

The influence of temporal scale selection on pelagic habitat biodiversity indicators

Abstract The development of biodiversity indicators is an integral component of forming marine strategies under the European Marine Strategy Framework Directive (MSFD). A key stage in the development of biodiversity indicators is the selection of an appropriate temporal scale over which to assess change in indicator state. This presents a particular challenge for the development of plankton indicators for assessing the state of pelagic habitats, due to the inherent stochasticity of plankton dynamics and the sensitivity of indicators to both climate-driven change and directly manageable pressures. Using two plankton indicator metrics, we demonstrate that the outcome of indicator assessments is inherently influenced by the temporal scale of the time-period over which the indicators are assessed. For example, we show that the inclusion of data from before a regime shift that occurred in the 1980s often alters the assessment of change compared to only including data from after the regime shift. We highlight that ultimately the appropriate temporal scale selected depends on the policy questions being addressed. We also suggest that reporting indicators over multiple temporal scales within an assessment helps provide information relevant to contemporary management, whilst also retaining crucial multi-decadal trends such as those caused by climate change.