Autumn Bloom Research Articles

Seasonal organic matter dynamics in a temperate shelf sea

Organic matter (OM) plays an important role in productive shelf seas and their contribution to global carbon (C) and nutrient cycles. We investigated dissolved and particulate OM (DOM and POM, respectively) dynamics over a seasonal cycle in the Celtic Sea. The quantity of OC was largest during the spring bloom and lowest in autumn. DOM was always C rich relative to the POM pool and the Redfield ratio (106C:16N:P). There was clear decoupling between C, N and P and the response of OM composition to different seasons and nutrient statuses of the microbial community. The C:P stoichiometry was much more variable than the C:N stoichiometry, which was near constant. Downward OC fluxes were dominated by POM during bloom events and DOM during the stratified summer. In terms of partitioning, 92–96% of OC was in the DOM pool throughout sampling, which given its high C:N (12.4–17) suggests it was an efficient vehicle for potential off-shelf export of C during winter mixing.

Phytoplankton bloom dynamics in turbid, well-mixed estuaries: A model study

To gain insight into mechanisms underlying phytoplankton bloom dynamics in turbid, well-mixed estuaries, experiments were conducted with an exploratory model that couples physical and biological processes. The motivation for choosing exploratory models is that they allow investigation of individual processes in isolation, therefore yielding fundamental insight into the mechanisms of the system. The Ems estuary (between the Netherlands and Germany) was selected as the prototype estuary, in which a zone of high turbidity is observed in the middle and upper reach. Results show that the model is capable of capturing the main features of the observed phytoplankton population density (P) patterns, that is, in the lower reach a spring bloom occurs, followed by a secondary bloom in autumn. Results of sensitivity studies reveal that the along-estuary distribution of suspended particulate matter (SPM) is a determining factor for the along-estuary location of blooms and it largely affects the intensity of blooms. The along-estuary advection of nutrients by the subtidal current is important for obtaining blooms with high intensities. In this model, the seasonally varying water temperature has a larger impact on the timing of spring blooms than the seasonally varying incident light intensity. The occurrence of an autumn bloom is due to the fact that during the summer season, the net specific growth rate of phytoplankton decreases. The latter is likely to result from an optimum water temperature (smaller than the maximum water temperature) for phytoplankton growth. Nevertheless, the occurrence and characteristics of autumn blooms are also influenced by seasonal variations in other aspects, for instance, loss of phytoplankton due to grazing.

Exploring mechanisms for spring bloom evolution: contrasting 2008 and 2012 blooms in the southwest Pacific Ocean

AbstractObservations from two research cruises made in 2008 and 2012 to east of New Zealand are put into context with satellite data to contrast and compare surface chlorophyll a evolution in the two years in order to explore mechanisms of phytoplankton bloom development in the southwest Pacific Ocean. In 2008, surface chlorophyll a largely followed the long-term climatological cycle, and 2008 can be considered a canonical year, where the autumn bloom is triggered by increasing vertical mixing at the end of summer and the spring bloom is triggered by decreasing vertical mixing at the end of winter. In contrast, 2012 was anomalous in that there was no autumn bloom, and in early spring there were several periods of sustained increase in surface chlorophyll a that did not become fully developed spring blooms. (In this region, we consider spring blooms to occur when surface chlorophyll a exceeds 0.5 mg m-3). These events can be related to alternating episodes of increased or decreased vertical mixing. The eventual spring bloom in October was driven by increased ocean cooling and wind stress (i.e. increased mixing) and paradoxically was driven by mechanisms considered more appropriate for autumn rather than spring blooms.

Mercury transformations in a coastal water column (Gulf of Trieste, northern Adriatic Sea)

The mechanisms of mercury (Hg) microbial transformations in coastal marine water column are poorly understood. In an effort to study seasonal Hg transformation mechanisms and underlying processes in the coastal marine ecosystem of the Gulf of Trieste (northern Adriatic Sea), we have successfully applied the 197Hg radiotracer technique in series of incubation experiments. This area is characterized by continuous Hg input from the Soča/Isonzo River as a consequence of nearly 500 years of activity at the Idrija Mine (W Slovenia). The method proved to be valuable, since it allowed us to follow Hg transformations at concentrations similar to those found in the study site. During our study, Hg methylation in the marine water column could not be detected, suggesting that sediments are the principal methylation site and the source of MeHg to the water column. Conversely, the water column showed a pronounced Hg reduction potential, mostly of photochemical origin, suggesting that the Gulf of Trieste is a source of Hg0 to the atmosphere. However, the high Hg reduction potential observed in autumn was most likely related to a phytoplankton (diatom) autumn bloom, indicated by high Chl a concentrations measured during that period. We hypothesize that the microbial reduction was either linked to the expression of mer genes or, a consequence of non-specific redox reactions. Variations in bacterioplankton community fingerprints (as determined by Denaturing Gradient Gel Electrophoresis) suggested that community structure had little influence on microbial Hg reduction potential. Nevertheless, our results indicate that in the absence of photochemistry, interactions between microbes and organic matter may enhance biogeochemical Hg2 + reduction potential in some coastal marine environments.

Physical and Biogeochemical Controls of the Phytoplankton Blooms in North Western Mediterranean Sea: A Multiplatform Approach Over a Complete Annual Cycle (2012–2013 DEWEX Experiment)

AbstractThe North Western Mediterranean Sea exhibits recurrent and significant autumnal and spring phytoplankton blooms. The existence of these two blooms coincides with typical temperate dynamics. To determine the potential control of physical and biogeochemical factors on these phytoplankton blooms, data from a multiplatform approach (combining ships, Argo and BGC‐Argo floats, and bio‐optical gliders) were analyzed in association with satellite observations in 2012–2013. The satellite framework allowed a simultaneous analysis over the whole annual cycle of in situ observations of mixed layer depth, photosynthetical available radiation, particle backscattering, nutrients (nitrate and silicate), and chlorophyll‐a concentrations. During the year 2012–2013, satellite ocean color observations, confirmed by in situ data, have revealed the existence of two areas (or bioregions) with comparable autumnal blooms but contrasting spring blooms. In both bioregions, the ratio of the euphotic zone (defined as the isolume 0.415 mol photons m−2 d−1, Z0.415) and the MLD identified the initiation of the autumnal bloom, as well as the maximal annual increase in [Chl‐a] in spring. In fact, the autumnal phytoplankton bloom might be initiated by mixing of the summer shallowing deep chlorophyll maximum, while the spring restratification (when Z0.415/MLD ratio became >1) might induce surface phytoplankton production that largely overcomes the losses. Finally, winter deep convection events that took place in one of the bioregions induced higher net accumulation rate of phytoplankton in spring associated with a diatom‐dominated phytoplankton community principally. We suggest that very deep winter MLD lead to an increase in surface silicates availability, which favored the development of diatoms.

Climate as a driver of increasing algal production in Lake of the Woods, Ontario, Canada

ABSTRACTPaterson AM, Rühland KM, Anstey CV, Smol JP. 2017. Climate as a driver of increasing algal production in Lake of the Woods, Ontario, Canada. Lake Reserv Manag. 33:403–414.Lake of the Woods (LOW) is a large, transboundary lake that straddles the provinces of Ontario and Manitoba, and the state of Minnesota. Although algal blooms have been reported in the lake since the early 1800s, monitoring data and anecdotal evidence suggest that toxic, cyanobacterial blooms have increased in frequency and intensity in recent years. However, total phosphorus inputs from the lake's primary tributary, the Rainy River, have declined significantly since the late 1960s. We explore this disconnect by examining spectrally-inferred determinations of chlorophyll a (Chl-a) in lake sediment cores, as a measure of past changes in aquatic primary production. Beginning in the late 1970s to early 1980s, inferred Chl-a increased at 5 impact sites in the north end of LOW that currently experience cyanobacterial blooms in late summer and autumn. In contrast, no change in Chl-a was observed at an oligotrophic reference site with much lower cyanobacteria biomass. At the impact sites, Chl-a generally showed no significant relationship to long-term trends in diatom-inferred total phosphorus concentrations, but was significantly and positively correlated to climatic variables, including mean annual air temperature at all sites and total annual precipitation at 4 sites. These data suggest that climate change may exacerbate algal blooms in this moderately-enriched lake. The results also show that the effects of climate change on aquatic production may be enhanced at sites with higher nutrient concentrations, likely because of positive feedbacks between cyanobacteria biomass, water temperature and nutrient availability. The impact of climate change should be considered carefully in future management initiatives.

Under the sea ice: Exploring the relationship between sea ice and the foraging behaviour of southern elephant seals in East Antarctica

Investigating ecological relationships between predators and their environment is essential to understand the response of marine ecosystems to climate variability and change. This is particularly true in polar regions, where sea ice (a sensitive climate variable) plays a crucial yet highly dynamic and variable role in how it influences the whole marine ecosystem, from phytoplankton to top predators. For mesopredators such as seals, sea ice both supports a rich (under-ice) food resource, access to which depends on local to regional coverage and conditions. Here, we investigate sex-specific relationships between the foraging strategies of southern elephant seals (Mirounga leonina) in winter and spatio-temporal variability in sea ice concentration (SIC) and coverage in East Antarctica. We satellite-tracked 46 individuals undertaking post-moult trips in winter from Kerguelen Islands to the peri-Antarctic shelf between 2004 and 2014. These data indicate distinct general patterns of sea ice usage: while females tended to follow the sea ice edge as it extended northward, the males remained on the continental shelf despite increasing sea ice. Seal hunting time, a proxy of foraging activity inferred from the diving behaviour, was longer for females in late autumn in the outer part of the pack ice, ∼150–370km south of the ice edge. Within persistent regions of compact sea ice, females had a longer foraging activity (i) in the highest sea ice concentration at their position, but (ii) their foraging activity was longer when there were more patches of low concentration sea ice around their position (either in time or in space; 30days & 50km). The high spatio-temporal variability of sea ice around female positions is probably a key factor allowing them to exploit these concentrated patches. Despite lack of information on prey availability, females may exploit mesopelagic finfishes and squids that concentrate near the ice-water interface or within the water column (from diurnal vertical migration) in the pack ice region, likely attracted by an ice algal autumn bloom that sustains an under-ice ecosystem. In contrast, male foraging effort increased when they remained deep within the sea ice (420–960km from the ice edge) over the shelf. Males had a longer foraging activity (i) in the lowest sea ice concentration at their position, and (ii) when there were more patches of low concentration sea ice around their position (either in time or in space; 30days & 50km) presumably in polynyas or flaw leads between land fast and pack ice. This provides access to zones of enhanced resources in autumn or in early spring such as polynyas, the Antarctic shelf and slope. Our results suggest that some seals utilized a highly sea ice covered environment, which is key for their foraging effort, sustaining or concentrating resources during winter.

Drivers of the autumn phytoplankton development in the open Black Sea

Abstract The dynamics of the autumn development of phytoplankton in the Black Sea were investigated using satellite-derived chlorophyll-a concentration (Chl), which was estimated for two regions in the deep sea over a 20-year period. We analysed 8-day composite Chl images along with changes in: (i) nutrient concentration obtained from in-situ measurements, (ii) sea surface temperature (SST), (iii) photosynthetically available radiation (PAR) obtained from satellite imagery, (iv) wind speed from the re-analysis of meteodata and (v) the depth of the upper mixed layer (UML) calculated from a 3D numerical model of the Black Sea. The peak in Chl was identified most frequently in the first half of November. A positive correlation between the duration of strong wind events and phytoplankton development was revealed, which was associated with the deepening of the UML, and replenishment of the photic zone with nutrients. The impact on phytoplankton was significant when the cumulative duration of strong wind (> 8 m s− 1) exceeded 60 h over the preceding 8 days. In such cases, the frequency of the Chl peaks increased up to 30–50% with an average of 20%. Strong wind was shown to determine the timing of the autumn bloom, but not its strength. From a positive relationship between the maximum Chl and nitrate concentration we found instead that the intensity of the autumn bloom was mainly defined by nitrate replenishment in the photic zone. On average, the timing of the seasonal maximum of Chl in the first half of November coincided with the deepening of the UML to the bottom of the seasonal thermocline (ca 25 m). Elution of nitrate from deeper layers, where its concentration is substantially higher, mitigated the nutrient limitation of phytoplankton growth. At the same time, a sharp decrease in PAR after mid-November resulted in the limitation of light for phytoplankton growth. Inter-annual variations of Chl in spring and autumn were shown not to be correlated. For example, the basin-wide autumn blooms were observed in some years when the spring blooms were absent. As the bloom cannot be based on regenerated nitrate, the amount of ‘new’ nitrate in the photic zone should have a positive trend in autumn. However, the sources and mechanisms of the basin-wide increase of nitrate concentration in the upper layer in autumn are not clear.

Effect of diatom morphology on the small-scale behavior of the copepod Temora stylifera (Dana, 1849)

We explored the small-scale behavior of the calanoid copepod Temora stylifera in relation to the diatoms Chaetoceros socialis, Leptocylindrus aporus, Leptocylindrus danicus and Pseudo-nitzschia calliantha offered as monospecific diets at similar carbon concentrations. These four diatoms are characterized by distinct size, shape and colony forming ability and are important components of the autumnal bloom co-occurring with the seasonal peak of T. stylifera abundance in Mediterranean coastal waters. High-speed video recordings showed that T. stylifera acquired cells in a suspension feeding mode while creating feeding currents. Copepod behavior was quantified in terms of feeding, motion, and grooming activities. T. stylifera spent more time in hovering than cruising in presence of all diets. The solitary L. aporus and P. calliantha elicited longer feeding bouts, lower appendage beat frequency and shorter grooming events compared to the colonial L. danicus and C. socialis. Overall the present results indicate that the behavioral responses of T. stylifera to different diatom diets were species-specific. The observed behavioral plasticity may help T. stylifera to adjust rapidly to changes in the food environment and this can be advantageous in exploiting short-lived phytoplankton blooms.

Shifting Trends in Bimodal Phytoplankton Blooms in the North Pacific and North Atlantic Oceans From Space With the Holo-Hilbert Spectral Analysis

Merged satellite ocean color data were used to examine trends in the timing and magnitude of phytoplankton blooms. Special emphasis was placed on the peak shift of spring and autumn/winter blooms in the North Pacific and North Atlantic Oceans with bimodal seasonal cycles. Ensemble empirical mode decomposition and Holo-Hilbert spectral analysis were combined to extract seasonal signals and investigate their modulation at multiple time-scales. In the temperate North Atlantic Ocean, earlier and decreasing spring blooms were detected with delayed and increased autumn blooms. The temperate North Pacific Ocean presented delayed and increased spring and autumn blooms, with the delay in fall blooms was larger than spring ones. The separation between two bloom peaks was increasing in both temperate North Atlantic and Pacific regions. The intrinsic variation in bloom timing and magnitude in these selected regions could be clearly extracted by ensemble empirical mode decomposition. Further Holo-Hilbert spectral results showed that changes in the annual cycle and bloom characteristics were modulated by interannual variability. These results suggest the critical role of interannual variability in the modulation of phytoplankton seasonality.

Seasonal phytoplankton blooms in the Gulf of Aden revealed by remote sensing

The Gulf of Aden, situated in the northwest Arabian Sea and linked to the Red Sea, is a relatively unexplored ecosystem. Understanding of large-scale biological dynamics is limited by the lack of adequate datasets. In this study, we analyse 15years of remotely-sensed chlorophyll-a data (Chl-a, an index of phytoplankton biomass) acquired from the Ocean Colour Climate Change Initiative (OC-CCI) of the European Space Agency (ESA). The improved spatial coverage of OC-CCI data in the Gulf of Aden allows, for the first time, an investigation into the full seasonal succession of phytoplankton biomass. Analysis of indices of phytoplankton phenology (bloom timing) reveals distinct phytoplankton growth periods in different parts of the gulf: a large peak during August (mid-summer) in the western part of the gulf, and a smaller peak during November (mid-autumn) in the lower central gulf and along the southern coastline. The summer bloom develops rapidly at the beginning of July, and its peak is approximately three times higher than that of the autumnal bloom. Remotely-sensed sea-surface temperature (SST), wind-stress curl, vertical nutrient profiles and geostrophic currents inferred from the sea-level anomaly, were analysed to examine the underlying physical mechanisms that control phytoplankton growth. During summer, the prevailing southwesterlies cause upwelling along the northern coastline of the gulf (Yemen), leading to an increase in nutrient availability and enhancing phytoplankton growth along the coastline and in the western part of the gulf. In contrast, in the central region of the gulf, lowest concentrations of Chl-a are observed during summer, due to strong downwelling caused by a mesoscale anticyclonic eddy. During autumn, the prevailing northeasterlies enable upwelling along the southern coastline (Somalia) causing local nutrient enrichment in the euphotic zone, leading to higher levels of phytoplankton biomass along the coastline and in the lower central gulf. The monsoon wind reversal is shown to play a key role in controlling phytoplankton growth in different regions of the Gulf of Aden.

Acidification and warming affect prominent bacteria in two seasonal phytoplankton bloom mesocosms.

In contrast to clear stimulatory effects of rising temperature, recent studies of the effects of CO2 on planktonic bacteria have reported conflicting results. To better understand the potential impact of predicted climate scenarios on the development and performance of bacterial communities, we performed bifactorial mesocosm experiments (pCO2 and temperature) with Baltic Sea water, during a diatom dominated bloom in autumn and a mixed phytoplankton bloom in summer. The development of bacterial community composition (BCC) followed well-known algal bloom dynamics. A principal coordinate analysis (PCoA) of bacterial OTUs (operational taxonomic units) revealed that phytoplankton succession and temperature were the major variables structuring the bacterial community whereas the impact of pCO2 was weak. Prokaryotic abundance and carbon production, and organic matter concentration and composition were partly affected by temperature but not by increased pCO2 . However, pCO2 did have significant and potentially direct effects on the relative abundance of several dominant OTUs; in some cases, these effects were accompanied by an antagonistic impact of temperature. Our results suggest the necessity of high-resolution BCC analyses and statistical analyses at the OTU level to detect the strong impact of CO2 on specific bacterial groups, which in turn might also influence specific organic matter degradation processes.

Influence of seasonal freshwater streamflow regimes on phytoplankton blooms in a Patagonian fjord

ABSTRACTLarge-scale regional phenomena and global climate trends may alter the freshwater discharge of large Patagonian rivers and could modify local circulation patterns in ways that influence phytoplankton dynamics. Modifications detected in the streamflow regime of the Puelo River (41.5° S, Patagonia, Chile) in recent decades may affect the regularity of seasonal phytoplankton blooms in Reloncaví Fjord. We examined the occurrence/frequency of spring–summer and autumn phytoplankton blooms in Reloncaví Fjord with respect to seasonal and inter-annual changes in freshwater streamflows from 2003 to 2011. Surface chlorophyll-a derived from satellite-ocean colour and phytoplankton abundances revealed that significant recurrences of autumn phytoplankton blooms (> 2 mg Chl-a m−3, > 500 cell mL−1) were associated with historical low mean freshwater streamflows, mainly in autumn (< 350 m3 s−1). On the other hand, the occurrence of spring–summer blooms was related to high streamflows (> 470 m3 s−1) that increased mixing in the upper photic layer enough to enhance phytoplankton growth. Our findings imply that the intensity of autumn blooms in Reloncaví Fjord could be modulated by streamflow strength.

Dynamics of the marine planktonic diatom family Chaetocerotaceae in a Mediterranean coastal zone

The planktonic diatoms belonging to two genera Chaetoceros and Bacteriastrum, included within the family Chaetocerotaceae, are ecologically important as they represent an important component of the phytoplankton in the coastal regions and are often among bloom-forming taxa. We analysed the chaetocerotacean species composition and abundances in the coastal area of northeastern Adriatic in a biweekly study conducted from September 2008 to October 2009 with the aim of investigating seasonal dynamics and species succession on a fine temporal scale and determining the most important ecological factors influencing their distribution. The study identified seven Chaetoceros and three Bacteriastrum species as major phytoplankton components showing the clear annual succession and two types of blooms (one species/multi species) governed by differing ecological conditions. Autumn bloom was composed of 20 chaetocerotacean species with Chaetoceros contortus and Chaetoceros vixvisibilis alternating in dominance. The summer period was characterized by spreading of freshwater from the Po River up to the eastern coast increasing availability of phosphate which triggered the monospecific Chaetoceros vixvisibilis bloom. We explained the chaetocerotacean dominant species succession pattern by the environmental parameters, with the temperature, salinity and phosphate availability as most important factors driving the species seasonality.

Proportion of marine organic carbon present in self-assembled gels along the subtropical front and its increase in response to reduced pH

Dissolved organic matter (DOM), the largest marine reservoir of reduced carbon, which contains a complex mix of polydisperse biopolymers and particularly small molecules in solution. However, we now know that about 10% of these dissolved moieties can spontaneously aggregate forming a huge mass of highly bioreactive microscopic particles by forming self-assembled gels (SAG) with a significant role in global carbon cycling. However, the effect of varying marine environments on DOM self-assembly remains virtually unknown. Here we report variations of the fraction of DOM that self-assemble forming gels (%SAG) measured in seawater samples collected during two different periods — before and during the autumn bloom— along the Subtropical Frontal Zone off New Zealand; an area characterized by strong spatiotemporal physicochemical and biological variability. Results show that %SAG varies in time and space. Measurements of %SAG ranged between 9–28% (14.5±5, mean±SD), and this broad variability could be partly associated to changes in phytoplankton biomass and/or UV radiation. Additional studies on the effect of a pH on the %SAG, reveal that small pH reductions of 0.3units can virtually double the %SAG from 14.5±5 to 27±7% (12.5±4%, mean±SD). The observed increase in the %SAG under reduced pH was observed in all samples, irrespectively of their origin. This outcome suggests that pH might be a critical parameter controlling the formation of gels in marine environments. Decreased pH increases the SW concentration of free ionized Ca ([Ca+2]), the prime DOM crosslinker. Rising [Ca+2] is likely responsible for the observed %SAG increase. The outcome that %SAG can be strongly affected by small changes in seawater properties, suggest that DOM self-assembly is remarkably responsive to subtle variations of environmental conditions. SAG are a leading source of bacterial nutrition and these observations have potentially strong ramifications in the ecology and biogeochemical cycles of the oceans.

Water mass characteristics and their temporal changes in a biological hotspot in the southern Chukchi Sea

Abstract. We analysed mooring and ship-based hydrographic and biogeochemical data obtained from a Hope Valley biological hotspot in the southern Chukchi Sea. The moorings were deployed from 16 July 2012 to 19 July 2014, and data were captured during spring and autumn blooms with high chlorophyll a concentrations. Turbidity increased and dissolved oxygen decreased in the bottom water at the mooring site before the autumn bloom, suggesting an accumulation of particulate organic matter and its decomposition (nutrient regeneration) at the bottom. This event may have been a trigger for the autumn bloom at this site. The bloom was maintained for 1 month in 2012 and for 2 months in 2013. The maintenance mechanism for the autumn bloom was also studied by hydrographic and biogeochemical surveys in late summer to autumn 2012 and 2013. Nutrient-rich water from the Bering Sea supplied nutrients to Hope Valley, although a reduction in nutrients occurred in 2012 by the influence of lower-nutrient water that would have remained on the Chukchi Sea shelf. In addition, nutrient regeneration at the bottom of Hope Valley could have increased nutrient concentrations and explained 60 % of its nutrient content in the bottom water in the autumn of 2012. The high nutrient content with the dome-like structure of the bottom water may have maintained the high primary productivity via the vertical nutrient supply from the bottom water, which was likely caused by wind-induced mixing during the autumn bloom. Primary productivity was 0.3 g C m−2 d−1 in September 2012 and 1.6 g C m−2 d−1 in September 2013. The lower productivity in 2012 was related to strong stratification caused by the high fraction of surface sea ice meltwater.

Seasonality, phytoplankton succession and the biogeochemical impacts of an autumn storm in the northeast Atlantic Ocean

Phytoplankton chemotaxonomic distributions are examined in conjunction with taxon specific particulate biomass concentrations and phytoplankton abundances to investigate the biogeochemical consequences of the passage of an autumn storm in the northeast Atlantic Ocean. Chemotaxonomy indicated that the phytoplankton community was dominated by nanoplankton (2–20μm), which on average represented 75±8% of the community. Microplankton (20–200μm) and picoplankton (<2μm) represented 21±7% and 4±3% respectively with the microplankton group composed of almost equal proportions of diatoms (53±17%) and dinoflagellates (47±17%). Total chlorophyll-a (TCHLa=CHLa+Divinyl CHLa) concentrations ranged from 22 to 677ngL−1, with DvCHLa making minor contributions of between <1% and 13% to TCHLa. Higher DvCHLa contributions were seen during the storm, which deepened the surface mixed layer, increased mixed layer nutrient concentrations and vertically mixed the phytoplankton community leading to a post-storm increase in surface chlorophyll concentrations. Picoplankton were rapid initial respondents to the changing conditions with pigment markers showing an abrupt 4-fold increase in proportion but this increase was not sustained post-storm. 19′-HEX, a chemotaxonomic marker for prymnesiophytes, was the dominant accessory pigment pre- and post-storm with concentrations of 48–435ngL−1, and represented 44% of total carotenoid concentrations. Accompanying scanning electron microscopy results support the pigment-based analysis but also provide detailed insight into the nano- and microplankton communities, which proved to be highly variable between pre-storm and post-storm sampling periods. Nanoplankton remained the dominant size class pre- and post-storm but the microplankton proportion peaked during the period of maximum nutrient and chlorophyll concentrations. Classic descriptions of autumn blooms resulting from storm driven eutrophication events promoting phytoplankton growth in surface waters should be tempered with greater understanding of the role of storm driven vertical reorganization of the water column and of resident phytoplankton communities. Crucially, in this case we observed no change in integrated chlorophyll, particulate organic carbon or biogenic silica concentrations despite also observing a ∼50% increase in surface chlorophyll concentrations which indicated that the surface enhancement in chlorophyll concentrations was most likely fed from below rather than resulting from in situ growth. Though not measured directly there was no evidence of enhanced export fluxes associated with this storm. These observations have implications for the growing practice of using chlorophyll fluorescence from remote platforms to determine ocean productivity late in the annual productivity period and in response to storm mixing.

Seasonal progression of microbial communities on the Faroe shelf

Microorganisms, such as phytoplankton and bacterioplankton, are affected by turnover rates of nutrients and show great fluctuations over seasons. In productive coastal areas, the biomass of bacterioplankton can be in the same range as that of phytoplankton. In these coastal areas the initiation and intensity of the spring bloom is highly variable between years. This variability is reflected in higher trophic levels and is therefore of major importance for ecosystems such as that of the Faroe Islands. However, one of the major unknown components is the bacterioplankton. We report a study on seasonal dynamics from March–September of nutrients, phytoplankton composition and their co-fluctuation with bacterial succession. For this purpose SAR11, Bacteroidetes, Roseobacter and cyanobacteria were relatively quantified using real-time PCR based on 16S DNA and total bacteria was assessed by epifluorescence microscopy. The phytoplankton species were identified using the inverted microscope technique. These data showed a pronounced diatom spring bloom and autumn bloom reflected by a corresponding decrease in nitrate and silicate (R2 = 0.72 and 0.77, respectively). The cessation of the phytoplankton bloom did not, however, seem to be explained by nutrient limitation. Roseobacter bloomed during the phytoplankton spring bloom, while the other bacterial groups increased during low phytoplankton biomass. This suggests that algal substrate availability and environmental conditions provide the opportunity for bacterial communities to develop a post-spring bloom. This study reveals how planktonic bacteria adapt with their surroundings, enhancing the microbial loop post-spring bloom and providing a potentially important food resource for higher trophic levels.

Multidecadal Field Data Support Intimate Links between Phytoplankton Dynamics and PCB Concentrations in Marine Sediments and Biota.

We analyzed three decades of field observations in the North Sea with additive models to infer spatiotemporal trends of chlorophyll a concentration, sediment organic carbon content, and polychlorinated biphenyls (PCBs) concentrations in mussels and sediments. By doing so, we separated long-term changes in PCB concentrations from seasonal variability. Using the inferred seasonal variability, we demonstrated that phytoplankton blooms in spring and autumn correspond to the annual maxima of the organic carbon content (r = 0.56; p = 0.004) and the PCB concentrations in sediments (r = 0.57; p = 0.004). Furthermore, we found a negative correlation between the PCB concentrations in sediments and in blue mussels (Mytilus edulis; r = -0.33, p = 0.012), which is probably related to the cleansing of the dissolved PCB phase driven by sinking organic matter during phytoplankton blooms and the filter-feeding behavior of the blue mussel. The present research demonstrates the role of seasonal phytoplankton dynamics in the environmental fate of PCBs at large spatiotemporal scales.

Warming, but not enhanced CO2 concentration, quantitatively and qualitatively affects phytoplankton biomass

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 528:39-51 (2015) - DOI: https://doi.org/10.3354/meps11264 Warming, but not enhanced CO2 concentration, quantitatively and qualitatively affects phytoplankton biomass Carolin Paul*, Birte Matthiessen, Ulrich Sommer GEOMAR Helmholtz-Centre for Ocean Research, Düsternbrooker Weg 20, 24105 Kiel, Germany *Corresponding author: cpaul@geomar.de ABSTRACT: We investigated the impacts of predicted ocean acidification and future warming on the quantity and nutritional quality of a natural phytoplankton autumn bloom in a mesocosm experiment. Since the effects of CO2-enrichment and temperature have usually been studied independently, we were also interested in the interactive effects of both aspects of climate change. Therefore, we used a factorial design with 2 temperature and 2 acidification levels in a mesocosm experiment with a Baltic Sea phytoplankton community. Our results show a significant time-dependent influence of warming on phytoplankton carbon, chlorophyll a, and particulate organic carbon. Phytoplankton carbon, for instance, decreased by more than half with increasing temperature at bloom time. Additionally, elemental carbon to phosphorus ratios (C:P) increased significantly, by approximately 5 to 8%, due to warming. Impacts of CO2 or synergetic effects of warming and acidification could not be detected. We suggest that stronger grazing pressure induced by temperature was responsible for the significant decline in phytoplankton biomass. Our results suggest that the biological effects of warming on Baltic Sea phytoplankton are considerable and will likely have fundamental consequences for trophic transfer in the pelagic food web. KEY WORDS: Phytoplankton biomass · Warming · Ocean acidification Full text in pdf format Supplementary material PreviousNextCite this article as: Paul C, Matthiessen B, Sommer U (2015) Warming, but not enhanced CO2 concentration, quantitatively and qualitatively affects phytoplankton biomass. Mar Ecol Prog Ser 528:39-51. https://doi.org/10.3354/meps11264 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 528. Online publication date: May 28, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.