North Atlantic Oscillation primary productivity and toxic phytoplankton in the Gullmar Fjord,Sweden (1985—1996)

The evaluation of the time-series data set of primary production, chlorophyll a (1985-1996) and toxic phytoplankton species abundance measurements (1986–1996) in the Gullmar Fjord as part of the Swedish Monitoring Program, revealed the importance of considering climatic and environmental forces among the factors that may be responsible for the observed fluctuations. The results suggested that the occurrence of toxic phytoplankton blooms in the Skagerrak may be related to changes in the phase of the North Atlantic Oscillation (NAO). The Dinophysis species were related to the NAO, temperature and salinity and the fluctuations in the phytoplankton biomass expressed as chlorophyll a were also shown to be related to the NAO. The results pointed to the need to understand further the role played by climatic and environmental forces in relation to the formation and duration of harmful algal blooms and the need for continuous quality monitoring programmes and novel statistical methods for detecting trends and cycles in ecological time-series related to environmental forces.     

122 Local to Coastal-Scale Macrophyte Community Structure: Surprizing Patterns and Possible Mechanisms

Diatom blooms may be initiated by cells that have survived in the plankton or germinated resting stages from the sediments. However, it is not well understood how these different inocula contribute to bloom development. We followed diatom community development in twenty-liter microcosms given different inocula. Surface sediment and phytoplankton were collected in Gullmar Fjord, Sweden. Replicate microcosms were then dosed with local sediment and/or plankton and incubated in situ in Gullmar Fjord. We also followed the concurrent development of the phytoplankton community in the fjord. Experiments run in both spring and fall 2002 showed that bloom development in the microcosms was significantly faster when seeded by planktonic cells. However, addition of sediment may have stimulated planktonic growth and also provided additional propagules. The type of inoculum used strongly influenced the diatom composition in the microcosms. Sediment additions, through germination of resting stages, resulted in communities dominated by Detonula confervacea and Thalassiosira minima in spring, and Skeletonema costatum in fall. Planktonic inocula resulted in blooms of T. nordenskioeldii and Chaetoceros debilis in spring, and S. costatum and several Chaetoceros spp. in fall. Microcosms dosed with both plankton and sediment showed a mixed species assemblage. Comparisons between the microcosms and fjord phytoplankton suggest an important role for benthic seeding of diatom blooms.     

121 Influence of Benthic vs. Pelagic Seeding on Coastal Diatom Bloom Development

Diatom blooms may be initiated by cells that have survived in the plankton or germinated resting stages from the sediments. However, it is not well understood how these different inocula contribute to bloom development. We followed diatom community development in twenty‐liter microcosms given different inocula. Surface sediment and phytoplankton were collected in Gullmar Fjord, Sweden. Replicate microcosms were then dosed with local sediment and/or plankton and incubated in situ in Gullmar Fjord. We also followed the concurrent development of the phytoplankton community in the fjord. Experiments run in both spring and fall 2002 showed that bloom development in the microcosms was significantly faster when seeded by planktonic cells. However, addition of sediment may have stimulated planktonic growth and also provided additional propagules. The type of inoculum used strongly influenced the diatom composition in the microcosms. Sediment additions, through germination of resting stages, resulted in communities dominated by Detonula confervacea and Thalassiosira minima in spring, and Skeletonema costatum in fall. Planktonic inocula resulted in blooms of T. nordenskioeldii and Chaetoceros debilis in spring, and S. costatum and several Chaetoceros spp. in fall. Microcosms dosed with both plankton and sediment showed a mixed species assemblage. Comparisons between the microcosms and fjord phytoplankton suggest an important role for benthic seeding of diatom blooms.     

Microsatellite markers for the palaeo-temperature indicator Pentapharsodinium dalei (Dinophyceae)

Pentapharsodinium dalei is a widely distributed cold-water dinoflagellate, which is used in palaeoecology as an indicator of relatively warmer conditions in polar and sub-polar regions. This species has been proposed to be one of the first indicators of global warming at high latitudes. We developed the first microsatellite markers for P. dalei to facilitate the study of spatial and temporal population genetic changes. Single cysts were isolated from surface sediments in Koljö Fjord, Sweden. After cyst germination, single vegetative cells were isolated for establishing monoclonal cultures. Six dinucleotide polymorphic microsatellite markers were developed as multiplex polymerase chain reactions and were genotyped in 32 strains. The number of alleles per locus varied between 4 and 12, and the estimated gene diversity varied from 0.588 to 0.891. The haploid state of the vegetative cells was confirmed. The six selected microsatellites will be useful to explore population dynamics in P. dalei from contemporary planktonic and revived benthic samples to enable, for example, detailed studies into the evolutionary consequences of anthropogenic and climate-driven habitat changes.     

Warmer,deeper, and greener mixed layers in the North Atlantic subpolar gyre over the last 50 years

Shifts in global climate resonate in plankton dynamics, biogeochemical cycles, and marine food webs. We studied these linkages in the North Atlantic subpolar gyre (NASG), which hosts extensive phytoplankton blooms. We show that phytoplankton abundance increased since the 1960s in parallel to a deepening of the mixed layer and a strengthening of winds and heat losses from the ocean, as driven by the low frequency of the North Atlantic Oscillation (NAO). In parallel to these bottom‐up processes, the top‐down control of phytoplankton by copepods decreased over the same time period in the western NASG, following sea surface temperature changes typical of the Atlantic Multi‐decadal Oscillation (AMO). While previous studies have hypothesized that climate‐driven warming would facilitate seasonal stratification of surface waters and long‐term phytoplankton increase in subpolar regions, here we show that deeper mixed layers in the NASG can be warmer and host a higher phytoplankton biomass. These results emphasize that different modes of climate variability regulate bottom‐up (NAO control) and top‐down (AMO control) forcing on phytoplankton at decadal timescales. As a consequence, different relationships between phytoplankton, zooplankton, and their physical environment appear subject to the disparate temporal scale of the observations (seasonal, interannual, or decadal). The prediction of phytoplankton response to climate change should be built upon what is learnt from observations at the longest timescales.     

Exploring the impact of multidecadal environmental changes on the population genetic structure of a marine primary producer

Many marine protists form resting stages that can remain viable in coastal sediments for several decades. Their long‐term survival offers the possibility to explore the impact of changes in environmental conditions on population dynamics over multidecadal time scales. Resting stages of the phototrophic dinoflagellate Pentapharsodinium dalei were isolated and germinated from five layers in dated sediment cores from Koljö fjord, Sweden, spanning ca. 1910–2006. This fjord has, during the last century, experienced environmental fluctuations linked to hydrographic variability mainly driven by the North Atlantic Oscillation. Population genetic analyses based on six microsatellite markers revealed high genetic diversity and suggested that samples belonged to two clusters of subpopulations that have persisted for nearly a century. We observed subpopulation shifts coinciding with changes in hydrographic conditions. The large degree of genetic diversity and the potential for both fluctuation and recovery over longer time scales documented here, may help to explain the long‐term success of aquatic protists that form resting stages.     

North Atlantic Oscillation influences on radial growth of Pinus pinea on the Italian mid-Tyrrhenian coast

The North Atlantic Oscillation (NAO) is the most important source of winter atmospheric variability in the northern hemisphere. NAO inversely reflects the precipitation regime, which plays a fundamental role in Mediterranean regions, e.g., by recharging the water table. As no attempt has been made thus far to analyze the relationship between NAO variability and tree radial growth in coastal Mediterranean conifers, this paper identifies the monthly, winter, annual, and decadal influence of NAO on tree-ring chronologies of six planted Pinus pinea L. populations distributed along the Tyrrhenian coasts of central Italy. Through multidimensional analyses, we identified tree-ring chronology associations in two main groups. The influence of NAO on the regional chronologies was identified with correlation functions for the comparison period between 1949 and 2003 at both annual and decadal timescales. Results indicate that winter NAO influence on radial tree growth at annual and decadal timescales may depend on geographical location, site characteristics, and the age structure of tree-ring chronologies. These results contribute to a better understanding of the P. pinea coastal forest ecology and provide evidence of large-scale climatic forcings that influence forest Mediterranean ecosystems.     

The Thiamine Content of Phytoplankton Cells Is Affected by Abiotic Stress and Growth Rate

Thiamine (vitamin B₁) is produced by many plants, algae and bacteria, but by higher trophic levels, it must be acquired through the diet. We experimentally investigated how the thiamine content of six phytoplankton species belonging to five different phyla is affected by abiotic stress caused by changes in temperature, salinity and photon flux density. Correlations between growth rate and thiamine content per cell were negative for the five eukaryotic species, but not for the cyanobacterium Nodularia spumigena. We demonstrate a high variability in thiamine content among phytoplankton species, with the highest content in N. spumigena. Salinity was the factor with the strongest effect, followed by temperature and photon flux density, although the responses varied between the investigated phytoplankton species. Our results suggest that regime shifts in phytoplankton community composition through large-scale environmental changes has the potential to alter the thiamine availability for higher trophic levels. A decreased access to this essential vitamin may have serious consequences for aquatic food webs.     

The influence of salinity in the domoic acid effect on estuarine phytoplankton communities

Toxic species of the diatom genus Pseudo-nitzschia, observed worldwide from coastal waters to the open ocean, produce the neurotoxin domoic acid (DA). DA is an important environmental and economic hazard due to shellfish contamination with subsequent effects on higher trophic levels. Previous research has demonstrated that, among other environmental factors, salinity influences the abundance and toxicity of Pseudo-nitzschia. In this study, the environmental factors driving the growth of Pseudo-nitzschia and the production of dissolved DA (dDA) in North Inlet estuary were examined. The effect of salinity on the growth inhibition of phytoplankton induced by the initial presence as well as by an addition of dDA was also assessed. Initially, the diatom abundance was negatively correlated with the abundance of Pseudo-nitzschia and with the concentration of dDA. With the addition of a concentrated solution of dDA, the percent inhibition of cryptophytes and diatoms was significantly correlated with salinity and suggested a higher sensitivity to dDA at extreme salinities. These results emphasize the importance of salinity in assessing the properties of DA and potentially of other phycotoxins on phytoplankton.     

Attached and Free-Floating Bacterioplankton in Howe Sound, British Columbia, a Coastal Marine Fjord-Embayment

Factors which influence the attachment of bacterioplankton to particles (including phytoplankton) were investigated by using (i) water samples removed from a coastal temperate fjord over an annual cycle and (ii) unialgal cultures of Prorocentrum minimum, Dunaliella tertiolecta, and Skeletonema costatum. Silt and salinity levels in this fjord seawater did not appear to influence bacterial attachment, but the percent attached bacteria was inversely related to both chlorophyll a concentrations and primary productivities. During periods of high primary productivities the percent attached bacteria was low, whereas during periods of low, increasing, and declining primary productivities the percent attached bacteria was high. A similar pattern of bacterial attachment was observed when the three phytoplankton were grown as batch cultures. The percent attached bacterial numbers increased upon the initiation of algal growth and after these cells stopped growing, but not while the algae were growing. We suggest that a major factor influencing the attachment of bacterioplankton is the physiological condition of their major nutrient source, the phytoplankton; mainly free-living bacteria are associated with growing phytoplankton, whereas a much greater proportion of the bacteria are attached among senescent phytoplankton populations.     

Factors controlling long-term changes of the eutrophicated ecosystem of Pärnu Bay,Gulf of Riga

Phytoplankton, mesozooplankton, mysids and fish larvae were studied during 15–29 annual cycles measured weekly to monthly in Pärnu Bay, the Gulf of Riga. The monthly variability of the biological data was related to temperature, ice conditions, salinity, influx of nutrients, the North Atlantic Oscillation (NAO) index, cloudiness and solar activity. Phytoplankton development was mainly a function of the NAO index. For the whole study period the abundance of zooplankton increased with increasing water temperature and solar activity. Significant correlations between phytoplankton and zooplankton densities were found until 1990. After the invasion of the predatory cladoceran Cercopagis pengoi in 1991, the zooplankton community was likely to be regulated by the introduced species rather than phytoplankton dynamics. The increased abundances of rotifers and copepods triggered the increase in mysid densities. The development of herring larvae was positively affected by the high density of copepods and rotifers but also by increased eutrophication. Until 1990 there was no significant relationship between the density of zooplankton and herring larvae. A negative relationship between the density of zooplankton and herring larvae in the 1990s suggests that the major shift in zooplankton community resulted in food limitation for herring larvae. The results indicated that (1) atmospheric processes in the northern Atlantic explain a large part of the interannual variation of the local phytoplankton stock, (2) trophic interactions control the development of pelagic communities at higher trophic levels, and (3) the introduction of an effective intermediate predator has repercussions for the whole pelagic food web in Pärnu Bay.     

Resting cysts,and effects of temperature and salinity on the growth of vegetative cells of the potentially harmful species Alexandrium insuetum Balech (Dinophyceae)

The potentially harmful species Alexandrium insuetum established by the incubation of resting cysts isolated from sediment trap samples collected at Jinhae-Masan Bay, Korea was characterized by morphological and phylogenetic analysis. The effects of temperature and salinity on the growth of A. insuetum were also investigated. The resting cysts are characterized by a spherical shape, a small size (20–25 μm) and the presence of either three or four red accumulation bodies. The similarity of morphological features of the resting cysts to those of other species of the minutum group (consisting of Alexandrium minutum and A. tamutum) indicates that the morphological features of resting cysts might improve the accuracy of the grouping of Alexandrium species. A. insuetum germinated from the resting cysts is morphologically consistent with vegetative cells reported from Korean and Japanese coastal areas, and has an partial large subunit (LSU) rDNA sequence identical to that from Japanese strains. The growth of A. insuetum was observed between salinity 20 and 35, with increasing temperature; however at 25 °C, A. insuetum could grow even at the salinity of 15. The highest growth rate (0.60 d⁻¹) was observed at 25 °C and the salinity of 25, which is higher than the previously reported growth rate of A. tamarense, which is responsible for outbreaks of paralytic shellfish poisoining and blooms in Jinhae-Masan Bay. These results suggest that the proliferation of A. insuetum in Jinhae-Masan Bay is likely to be highest during the summer.     

Variation within and between cyanobacterial species and strains affects competition: Implications for phytoplankton modelling

Cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii are two harmful species which co-occur and successively dominate in freshwaters globally. Within-species strain variability affects cyanobacterial population responses to environmental conditions, and it is unclear which species/strain would dominate under different environmental conditions. This study applied a Monte Carlo approach to a phytoplankton dynamic growth model to identify how growth variability of multiple strains of these two species affects their competition.Pairwise competition between four M. aeruginosa and eight C. raciborskii strains was simulated using a deterministic model, parameterized with laboratory measurements of growth and light attenuation for all strains, and run at two temperatures and light intensities. 17 000 runs were simulated for each pair using a statistical distribution with Monte Carlo approach.The model results showed that cyanobacterial competition was highly variable, depending on strains present, light and temperature conditions. There was no absolute ‘winner’ under all conditions as there were always strains predicted to coexist with the dominant strains, which were M. aeruginosa strains at 20 °C and C. raciborskii strains at 28 °C. The uncertainty in prediction of species competition outcomes was due to the substantial variability of growth responses within and between strains. Overall, this study demonstrates that within-species strain variability has a potentially large effect on cyanobacterial population dynamics, and therefore this variability may substantially reduce confidence in predicting outcomes of phytoplankton competition in deterministic models, that are based on only one set of parameters for each species or strain.     

Structure of the phytoplankton communities in two lagoons of different salinity in the Sfax saltern (Tunisia)

The structure and ecophysiological characteristics of phytoplanktonassemblages were studied for 10 months in two lagoons of differentsalinity (40 and 90) in the saltern of Sfax (Tunisia), in relationto environmental factors. These assemblages were largely dominatedby diatoms and dinoflagellates, which accounted for >90%of total abundance. A principal components analysis clearlydifferentiated the observations made in the two lagoons, thedominant correlate being the salinity. Euryhaline species andparticularly diatoms developed preferentially in the less salinelagoon, and were largely replaced by stenohaline species representedby dinoflagellates, which were dominant in the more saline lagoon.Calculation of the pigment diversity index and the species diversityindex showed that the phytoplankton assemblages studied werepermanently in a juvenile stage, as the species restructuringrelated to environmental constraints did not allow them to reachthe climax stage at any given time in their development. Despitethe heavy constraint imposed by the salinity, it is evidentthat other environmental factors, e.g. temperature, play a rolein the regulation of the planktonic communities. Finally, thedifference in the size distribution of the total microbial biomass,estimated by the assay of particulate proteins, showed thatthere was a significant change in the community structure andthe planktonic trophic networks, in parallel with the increasein salinity.     

The viability of a plant “on the edge”: Glaucium flavum (Papaveraceae) in Norway

The prospects for persistence of Glaucium flavum in Norway were evaluated by integrating data concerning spatio‐temporal distribution, plant growth and development, reproduction, dispersal, seed bank and genetic variability. The distribution of Glaucium flavum in the Oslo Fjord region is much more restricted now than before. Out of the formerly recorded 35 populations, only eight populations were present in 1998, all in the outer parts of the fjord. The species is a short‐lived iteroparous perennial in Norway. This growth habit gives high reproductive output from fertile individuals. G. flavum is self‐compatible and can easily reproduce even in small populations. The ability to disperse long distances on water is limited. The observed seed bank will therefore enhance survival. No variation in isoenzymes was observed neither within nor among the G. flavum populations in the Oslo Fjord region. The species should be considered Endangered in Norway, according to the criteria given by IUCN.     

The relationship between phytoplankton distribution and water column characteristics in North West European shelf sea waters

Phytoplankton underpin the marine food web in shelf seas, with some species having properties that are harmful to human health and coastal aquaculture. Pressures such as climate change and anthropogenic nutrient input are hypothesized to influence phytoplankton community composition and distribution. Yet the primary environmental drivers in shelf seas are poorly understood. To begin to address this in North Western European waters, the phytoplankton community composition was assessed in light of measured physical and chemical drivers during the "Ellett Line" cruise of autumn 2001 across the Scottish Continental shelf and into adjacent open Atlantic waters. Spatial variability existed in both phytoplankton and environmental conditions, with clear differences not only between on and off shelf stations but also between different on shelf locations. Temperature/salinity plots demonstrated different water masses existed in the region. In turn, principal component analysis (PCA), of the measured environmental conditions (temperature, salinity, water density and inorganic nutrient concentrations) clearly discriminated between shelf and oceanic stations on the basis of DIN:DSi ratio that was correlated with both salinity and temperature. Discrimination between shelf stations was also related to this ratio, but also the concentration of DIN and DSi. The phytoplankton community was diatom dominated, with multidimensional scaling (MDS) demonstrating spatial variability in its composition. Redundancy analysis (RDA) was used to investigate the link between environment and the phytoplankton community. This demonstrated a significant relationship between community composition and water mass as indexed by salinity (whole community), and both salinity and DIN:DSi (diatoms alone). Diatoms of the Pseudo-nitzschia seriata group occurred at densities potentially harmful to shellfish aquaculture, with the potential for toxicity being elevated by the likelihood of DSi limitation of growth at most stations and depths.     

Food availability outweighs ocean acidification effects in juvenile Mytilus edulis: laboratory and field experiments

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless, in many coastal areas high pCO₂ variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12–20 g kg^?1) and CO₂ enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual pCO₂ variability in this habitat and the combined effects of elevated pCO₂ and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of pCO₂ up to 3350 μatm. Kiel Fjord was characterized by strong seasonal pCO₂ variability. During summer, maximal pCO₂ values of 2500 μatm were observed at the surface and >3000 μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high pCO₂ inner fjord field station (mean pCO₂ ca. 1000 μatm) in comparison to a low pCO₂ outer fjord station (ca. 600 μatm). In addition, mussels were able to out‐compete the barnacle Amphibalanus improvisus at the high pCO₂ site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater pCO₂. At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus, M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus. We conclude that benthic stages of M. edulis tolerate high ambient pCO₂ when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification.     

Abiotic drivers of interannual phytoplankton variability and a 1999–2000 regime shift in the North Sea examined by multivariate statistics

The Dutch coastal zone is a region of the North Sea with a marked interannual and long‐term abiotic and phytoplankton variability. To investigate the relationship between abiotic variability and phytoplankton composition, two routine water monitoring data sets (1991–2005) were examined. Multivariate statistics revealed two significant partitions in the data. The first consisted of interannual abiotic fluctuations that were correlated to Rhine discharge that affected the abundance of summer and autumn diatom species. The second partition was caused by a shift in the abiotic data from 1998 to 1999 that was followed by a shift in phytoplankton composition from 1999 to 2000. Important factors in the abiotic shift were decreases in suspended matter (SPM) and phosphate (DIP) concentrations, as well as in pH. The decrease in SPM was caused by a reduction in wind speed. The increase in water column daily irradiance from the decrease in SPM led to increases in the abundance of winter–spring species, notably the prymnesiophyte Phaeocystis globosa. Because wind speed is related to the North Atlantic Oscillation (NAO) index it was possible to correlate NAO index and P. globosa abundance. Only five abiotic variables representing interannual and long‐term variability, including Rhine discharge and NAO index, were needed to model the observed partitions in phytoplankton composition. It was concluded that interannual variability in the coastal phytoplankton composition was related to year‐to‐year changes in river discharge while the long‐term shift was caused by an alternating large‐scale meteorological phenomenon.     

Etudes expérimentalles sur la sensibilité du phytoplancton d'eau douce aux variations de salinité dans le fjord du Saguenay (Estuaire du St-Laurent), Canada Experimental Studies on the Susceptibility of Freshwater Phytoplankton to Variation of Salinity in the Fjord of Saguenay (St. Lawrence Estuary), Canada

The Saguenay Fjord is characterized by very high run-offs. The annual flow varies between 1.2 and 4.2 × 10³ m³ . s⁻¹. During the summer the surface salinity shows a sharp horizontal gradient (from 1 0/00 to 20 0/00). The surface phytoplankton, mainly freshwater and even some euryhaline species is submitted to salinity stress. Continuous culture experiments were conducted to study the susceptibility of this freshwater phytoplankton under different salinity conditions. Some pennate diatoms (dominant group) are found as relatively tolerant to salinity. Microflagellates have been found to be resistant to salinity up to 26 0/00. Chlorophyll concentrations and rates of primary production of those organisms are as high as those of the control.     

Control of modern dinoflagellate cyst distribution in the Irish and Celtic seas by seasonal stratification dynamics

Surface sediments from seven stations located in the seasonally stratified, frontal and mixed water regions in the Celtic and Irish seas have been analysed for their dinoflagellate cyst assemblages and dinosterol content. A total of 45 dinoflagellate cyst taxa have been identified and the assemblages related to surface and sediment conditions. Sediments from the mixed water region, at 30 m water depth, are characterised by a relatively low cyst concentration (∼2300 cysts/g dry weight) and high relative abundances of Lingulodinium machaerophorum accompanied by Spiniferites membranaceus, Brigantedinium spp. and Dubridinium caperatum. Assemblages from stratified and frontal water stations are dominated by Spiniferites ramosus associated with Operculodinium centrocarpum, Brigantedinium spp., cysts of Polykrikos schwartzii and Selenopemphix quanta. Ordination techniques performed on a restricted number of 35 taxa from the assemblages differentiated the stratified and frontal assemblages based on the abundance of the less abundant species Bitectatodinium tepikiense and Spiniferites elongatus. Among the environmental parameters (sea-surface temperature and salinity, stratification index, chlorophyll concentration and sediment grain-size classes), the seasonal stratification and sedimentological context, itself a function of tidal dynamics, explain most of the variance in the environmental conditions. These results indicate that dinoflagellate cyst analyses of shelf sediment records can be used to document the planktonic signal of seasonal stratification dynamics.