Showing papers in "Journal of Plankton Research in 2012"
TL;DR: The key parts of optimal annual routine models are described and how the models can be used to study phenology, life-history strategies, and population dynamics; predict responses to environmental change; and guide future zooplankton studies.
Abstract: Behaviour and life-history strategies of zooplankton have evolved in response to seasonal cycles in food availability, predation risk and abiotic conditions. A key challenge is to understand how different activities over the year are linked. For instance, how does a change in spring activities, such as the timing or amount of egg production, influence autumn activities, for instance energy storage or migration? Trade-offs viewed in relation to individual lifetime fitness consequences couple these events. The framework of optimal annual routines provides theory and methodology for consistent analyses of these temporal trade-offs. Here I describe the key parts of optimal annual routine models and how the models can be used to: (i) study phenology, life-history strategies, and population dynamics; (ii) predict responses to environmental change; and (iii) guide future zooplankton studies. I mainly discuss the adaptations of zooplankton species inhabiting high latitude oceans where the seasonal cycle and its effects are particularly strong. Empirical challenges include issues of seasonal resolution, state-dependent processes and individual variability. Two ecological problems with avenues for future work are discussed in particular detail: the role of sea ice and ice algae in the life cycle of copepods and krill, and the adaptive value and ecological consequences of semelparous versus iteroparous reproductive strategies.
99 citations
TL;DR: Although some issues remain and there is no universal method, the Neutral Red vital stain proved the most robust viability method in this study and is broadly applicable to both phytoplankton and zooplankon larger than 50 m.
Abstract: The rapid and efficient analysis of plankton samples (e.g. enumeration, identification, biomass determination) has been an important driver for recent technological developments in (semi-) automated analysis and imaging instruments. Most focus has been on identification and abundance estimates, while less attention has been given to viability, i.e. the assessment of whether the organisms are dead or alive. However, a wide spectrum of scientific applications requires accurate viability determinations, e.g. the monitoring of invasive species in ship ballast water. The transfer of species through ballast water forms a major threat to marine ecosystems, resulting in significant environmental and economic losses. A variety of viability stains and viability assessment methods are available, but there has been no systematic investigation how these methods perform for larger organisms (epsilon 50 m). We review the current procedures for viability determination for large plankton and present a cross-comparison of three methods: cell digestion assay (CDA), SYTOX Green nucleic acid staining and Neutral Red vital staining. The CDA and SYTOX Green methods did not perform well and gave various problems linked to the multicellular nature of zooplankton, autofluorescence and/or constraints set by the definition of cell death. Although some issues remain and there is no universal method, the Neutral Red vital stain proved the most robust viability method in this study and is broadly applicable to both phytoplankton and zooplankton larger than 50 m.
97 citations
TL;DR: In this paper, a consistent quantitative time series of thesea-surface fronts detected from satellite-detected datasets of SST and Chl for the domain of the CaliforniaCurrent (16-458N, 140-1008W) was created.
Abstract: SUMMARY We created a consistent quantitative time series of thesea-surface fronts detected from satellite-detected datasets of SST and Chl for the domain of the CaliforniaCurrent (16–458N, 140–1008W) that is 29 years longfor SST and 14 years long for Chl. While the methodsused here for front detection are objective, the resultsdepend on a multitude of details of application and onthe type and quality of satellite data being used. In spiteof these shortcomings, we believe that the time series offrontal frequencies are objective characteristics of thesystem. Because of the extensive and frequent cloudcover, we had to composite (average) the daily distribu-tions of fronts into monthly mean distributions normal-ized by the number of cloud-free images. Thesemonthly time series of front frequencies have a signifi-cant error component due to missing data, and theerror is bigger offshore where the frequency of cloud-free days is lower.In this region, major SST fronts always coincide withChl fronts, but the across-front contrast is variable forSST and Chl. Therefore, not all SST fronts are detectedas Chl fronts, and vice versa. Compounded with the dif-ferent coverage of various satellite sensors, this producesdifferent spatial and temporal statistics for the SST andChl fronts. While both SST and Chl fronts are affected
89 citations
TL;DR: Ohman et al. as mentioned in this paper analyzed the abundance of mesozooplankton and suspended particulate matter across the deep-water "A-Front" in the southern sector of the California Current System.
Abstract: Author(s): Ohman, MD; Powell, JR; Picheral, M; Jensen, DW | Abstract: We analyzed the abundance of mesozooplankton and suspended particulate matter across the deep-water "A-Front" in the southern sector of the California Current System. We characterized the A-Front with two novel devices, a free-fall Moving Vessel Profiler (MVP) and an Underwater Vision Profiler 5 (UVP5), together with quantitative bongo samples analyzed by ZooScan. The MVP permitted real-time visualization of vertical density structure, chlorophyll a fluorescence and particle size structure (from a laser optical particle counter) across the front to a depth of 200 m with the research vessel moving at 6 m s-1. The UVP5 quantified in situ vertical distributions from digital images of planktonic organisms and particles in profiles to 300 m. Both the MVP and UVP5 indicated that organic aggregates increased several-fold at the A-Front. The A-Front was a region of elevated abundance of mainly particle-grazing mesozooplankton, including calanoid copepods, Oithona spp., appendicularians and euphausiids, as well as a site of elevated ratio of nauplii copepod-1. In contrast, poecilostomatoid copepods, ostracods, chaetognaths and radiolaria, most of which are more carnivorous or omnivorous, were all elevated in abundance to the south of the front. We provide evidence that submesoscale fronts can be regions of locally elevated plankton abundance and production, as well sites of faunal transitions. © 2012 The Author.
85 citations
TL;DR: Evidence for active feeding of Noctiluca on Southern Ocean phytoplankton is provided, suggesting possible competition with other grazers may have implications for food web dynamics were NoctILuca to become established in the Southern Ocean.
Abstract: We describe a climate-driven range expansion of the red-tide dinoflagellate Noctiluca scintillans into the Southern Ocean (45°31′S 147°E). Sea surface height data showed that a warm-core eddy moving southwards from Tasmania was the potential vector for the transport of Noctiluca. We provide evidence for active feeding of Noctiluca on Southern Ocean phytoplankton. Possible competition with other grazers may have implications for food web dynamics were Noctiluca to become established in the Southern Ocean.
78 citations
TL;DR: Offspring viability was not affected by 1000 ppm CO2-acidified seawater, whereas the effects of 2 and 4°C warming were dependent upon the batch of eggs used; warming increased viability in the second batch.
Abstract: We examined how predicted end of century ocean warming and acidification scenarios affected the incidence of apoptosis in the eggs and nauplii of the copepod Calanus helgolandicus. Offspring viability was not affected by 1000 ppm CO2-acidified seawater, whereas the effects of 2 and 4°C warming were dependent upon the batch of eggs used; warming increased viability in the second batch. This context-dependency highlights the need for cautious interpretation and application of data from individual climate-change studies.
71 citations
TL;DR: In this article, the phytoplankton of the River Loire, a relatively unregulated river in Western Europe, was investigated by investigating the factors controlling the composition and dynamics in this river.
Abstract: Most studies of phytoplankton dynamics in lowland rivers have been conducted inregulated rivers. This study deals the phytoplankton of the River Loire, a relativelyunregulated river in Western Europe, and aims at investigating the factors control-ling phytoplankton composition and dynamics in this river. Phytoplankton biodi-versity was assessed by pooling data from monthly sampling for 8 years at differentsites. A correspondence analysis showed temporal and longitudinal gradients, witha dominance of small centric diatoms and green algae for most of the year, in themiddle and lower river sectors. Phytoplankton dynamics were further exploredusing the POTAMON simulation model, run for the year 2005. The simulations,in agreement with the observations, confirmed the virtual absence of aStephanodiscus spring peak, and reproduced well the development of small centricdiatoms and green algae. Production and loss rates calculated by the modelhelped us to explain the dynamics of the three main phytoplankton categories,which attained high net production rates due to the low river depth ( 1 m at lowdischarge), but were subject to high sedimentation losses. Model calculations alsoshowed that P limitation was likely, particularly for green algae, with a reductionof growth rate of up to 35%. In addition, the simulations showed a significantimpact of the invasive Asian clam, Corbicula spp., on phytoplankton biomass. Thisstudy shows that the factors determining phytoplankton diversity and dynamics inthis unregulated river are basically the same as those identified in other lowlandrivers, but that key factors are habitat diversity and variation of water level in theriver channel.KEYWORDS: potamoplankton; lowland river; diversity; dynamics; nutrientlimitation
69 citations
TL;DR: Landry et al. as mentioned in this paper investigated community composition and biomass across a sharp frontal gradient overlying deep waters south of Point Conception, California, and found that the frontal interface was strongly enriched and uniquely defined by a subsurface bloom of large diatoms, elevated concentrations of suspension-feeding zooplankton, high bioacoustical estimates of pelagic fish and enhanced bacterial production and phytoplankon biomass and photosynthetic potential.
Abstract: Author(s): Landry, MR; Ohman, MD; Goericke, R; Stukel, MR; Barbeau, KA; Bundy, R; Kahru, M | Abstract: In October 2008, we investigated pelagic community composition and biomass, from bacteria to fish, across a sharp frontal gradient overlying deep waters south of Point Conception, California. This northsouth gradient, which we called A-Front, was formed by the eastward flow of the California Current and separated cooler mesotrophic waters of coastal upwelling origin to the north, from warm oligotrophic waters of likely mixed subarcticsubtropical origin to the south. Plankton biomass and phytoplankton growth rates were two to three times greater on the northern side, and primary production rates were elevated 5-fold to the north. Compared with either of the adjacent waters, the frontal interface was strongly enriched and uniquely defined by a subsurface bloom of large diatoms, elevated concentrations of suspension-feeding zooplankton, high bioacoustical estimates of pelagic fish and enhanced bacterial production and phytoplankton biomass and photosynthetic potential. Such habitats, though small in areal extent, may contribute disproportionately and importantly to regional productivity, nutrient cycling, carbon fluxes and trophic ecology. As a general introduction to the A-Front study, we provide an overview of its design and implementation, a brief summary of major findings and a discussion of potential mechanisms of plankton enrichment at the front. © 2012 The Author.
67 citations
TL;DR: The results show three assemblages sharply delineated in space, with plankton in the front being compositionally distinct and biomass elevated relative to either of the adjacent water masses.
Abstract: Spatial variability of plankton biomass, community composition and size structurewas investigated across a strong frontal transition (A-Front) in the southernCalifornia Current Ecosystem in October 2008. Depth profiles were taken across a25-km transect of nine stations sampled semi-synoptically during one night andfor 3 days following drifter arrays in the adjacent water masses. Community com-positions are compared based on analyses by digital epifluorescence microscopy,flow cytometry and pigment composition by high-pressure liquid chromatography.Our results show three assemblages sharply delineated in space, with plankton atthe front being compositionally distinct and biomass elevated relative to either ofthe adjacent water masses. Depth-averaged chlorophyll a (Chl a) varied by a factorof 2.3 (0.35–0.81 mg Chl a L
65 citations
TL;DR: A new perspective on the role of lipid phase transitions in zooplankton is proposed, with solid – liquid phase transitions of lipids being a factor regulating their buoyancy.
Abstract: A new perspective on the role of lipids in zooplankton is proposed, with solid – liquid phase transitions of lipids being a factor regulating their buoyancy. These phase transitions are controlled by zooplankton in relation to their physical environment, through the selective accumulation of specific lipids with optimum levels of unsaturation. The necessity to control buoyancy and maintain an optimum depth is a fundamental evolutionary force, driving anatomical, biochemical and behavioural adaptations of all organisms within the aquatic realm. It is hypothesized that each species adjusts the amount, composition and anatomical location of lipids, to maximize fitness according to their preferred habitat and life history traits. Recent discoveries regarding the role of phase transitions of lipids in marine zooplankton and their role in regulating buoyancy will require re-interpretation of existing data and stimulate future scientific endeavours in zooplankton research.
60 citations
TL;DR: This work demonstrates how the accuracy of a state-of-the-art technique for plankton classification can be improved up to 86% if a previous automated step designed to remove non-living images is included and shows how the classification method can be adapted to provide not only taxonomic but also the morphological classification of cells in order to obtain a more reliable estimate of biovolume.
Abstract: The most commonly used biomass estimate for microalgae is obtained from cell biovolume, usually calculated from microscopically measured linear dimensions. Although reliable, this is a highly time-consuming and specialized technique. Automated sampling devices that acquire images of cells and use pattern recognition techniques to identify the images have been developed as an alternative to microscopy-based methods. There are some aspects of automatic sampling and classification methods, however, which can be improved for the analysis of field samples including living and non-living particles. In this work, we demonstrate how the accuracy of a state-of the-art technique for plankton classification (Support Vector Machine) can be improved up to 86% if a previous automated step designed to remove non-living images is included. There is a tendency with the currently applied automatic methods to misestimate cell biovolume due to the two-dimensionality of the images. Here, we present a data set of more than 500 samples to show that the greatest effect is caused by the incorrect estimation of biovolume of the chain-forming diatoms. This results in an overestimate of biomass of between 20 and 100% where chain-forming diatoms represent more than the 20% of the biomass of the sample. We show how the classification method can be adapted to provide not only taxonomic but also the morphological classification of cells in order to obtain a more reliable estimate of biovolume according to the predicted cell shape, in a way comparable with microscopy-based estimates.
TL;DR: The cosmopolitan distribution of the marine planktonic diatom Chaetoceros socialis Lauder is generally interpreted as a case of wide ecological plasticity, but cryptic diversity has recently been found.
Abstract: The cosmopolitan distribution of the marine planktonic diatom Chaetoceros socialis Lauder is generally interpreted as a case of wide ecological plasticity. However, cryptic diversity has recently b ...
TL;DR: The results suggest that compounds produced by C. raciborskii may induce defense mechanisms in M. aeruginosa, the first report on colony induction resulting from the interaction between cyanobacteria, and indicates specificity in this interaction.
Abstract: In a tropical reservoir, the cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii are the dominant species, with changes in dominance throughout the year. Since allelopathy has been suggested as a factor that could promote or stabilize harmful algal blooms, we investigated potential allelopathic effects of C. raciborskii on M. aeruginosa. Microcystis aeruginosa was exposed to exudates of a C. raciborskii monoculture and exudates of mixed cultures of both species. Significant growth inhibition of M. aeruginosa was observed only when it was exposed to exudates from the mixed culture with high proportion of C. raciborskii. This result suggests that the production of growth inhibitors seems to depend on stress (competition) and on the density of the producer species. In contrast to the control, M. aeruginosa formed colonies when exposed to filtrates of mixed cultures. As far as we know, this is the first report on colony induction resulting from the interaction between cyanobacteria. Our results suggest that compounds produced by C. raciborskii may induce defense mechanisms in M. aeruginosa. Our results also indicate specificity in this interaction, since another strain of M. aeruginosa showed different responses.
TL;DR: Li et al. as mentioned in this paper used data-driven diagnostic biogeochemical models to quantify how the front-induced physical mixing influenced the production, grazing and transport of phytoplankton carbon in the southern California Current.
Abstract: Author(s): Li, QP; Franks, PJS; Ohman, MD; Landry, MR | Abstract: Processes that occur at mesoscale and submesoscale features such as eddies and fronts are important for marine ecosystem dynamics and biogeochemical fluxes. However, their impacts on the fate of biogenic organic carbon in coastal oceans are not well quantified because physical and biological interactions at such features are very complex with short time-and small spatial scales variability. As part of the California Current Ecosystem Long-Term Ecological Research (CCE-LTER) Process studies in the southern California Current in October 2008, we sampled across a strong temperature and chlorophyll front ('A-Front') separating water masses with distinct hydrographic and biogeochemical characteristics and a modified biological assemblage at the frontal interface. Thorpe-scale analyses of the hydrographic data from a free-fall moving vessel profiler suggested an increased diapycnal diffusive nitrate flux at the front zone. Based on these field data, we use data-driven diagnostic biogeochemical models to quantify how the front-induced physical mixing influenced the production, grazing and transport of phytoplankton carbon in the southern California Current. Our results suggest that enhanced diffusive diapycnal fluxes of nutrients stimulated phytoplankton primary production at the front; this effect, together with reduced microzooplankton grazing, increased net growth of the phytoplankton community leading to locally enhanced biomass of large phytoplankton, such as diatoms, in the frontal zone. © 2012 The Author.
TL;DR: Principal components analysis of copepods and their diets showed cultured Calanus spp.
Abstract: Tisbe furcata, Nitokra lacustris, Calanus finmarchicus and Calanus glacialis were reared for several months in the laboratory prior to feeding selected diets. Copepods were fed Isochrysis galbana, Tetraselmis sp., Dunaliella tertiolecta, Thalassiosira pseudonana, Rhodomonas sp., Rhodomonas lens and Oxyrrhis marina individually or in combination. Oxyrrhis marina itself was fed up to four of the algae species. The lipid class and fatty acid composition of the copepods was determined and compared with each other, the diets and with wild C. finmarchicus, C. glacialis and Pseudocalanus sp. Cultured O. marina, T. furcata and N. lacustris had greater proportions of essential 22:6v3 or 20:5v3 acids than in their diets suggesting nutritional enrichment through synthesis or preferential retention. Lower proportions of 18:3v3 than in their diets fed individually or in combination suggests desaturation and elongation of 18:3v3. Stable isotope analysis of the heterotroph samples and their dietary sources revealed similar values for 18:3v3 in each dietary pair and different ones for 22:6v3 and 20:5v3 supporting derivation from precursors rather than trophic magnification. Principal components analysis of copepods and their diets showed cultured Calanus spp. to have the most similar fatty acid composition to their diet indicating little modification or sequestration of polyunsaturated fatty acids.
TL;DR: In this paper, the environmental conditions and mesozooplankton community were monitored during summer cruises in 2003, 2004 and 2006-2008 in the northern Gulf of Mexico.
Abstract: The environmental conditions and mesozooplankton community were monitored during summer cruises in 2003, 2004 and 2006–2008 in the northern Gulf of Mexico. Data were collected on temperature, salinity, dissolved oxygen, chlorophyll-a and zooplankton taxonomic abundances. Environmental conditions were largely related to the influence of the Mississippi River plume. The zooplankton community was numerically dominated by copepods, with various meroplankton and other non-copepod zooplankton present in lower abundances. Cluster analysis revealed four distinct groups of co-occurring zooplankton taxa. Two of these were numerically dominant, one characterized by the copepod Acartia spp. and a second consisting of several copepod taxa (including larger-bodied genera) and salps. Relative to the group containing Acartia spp., this second dominant group was more abundant at higher salinity, lower temperature and greater vertical extent of hypoxic water into the water column above the seafloor. Dissolved oxygen, as vertical extent of hypoxia, was of comparable importance to temperature and salinity in predicting the abundances of zooplankton taxa. Variability of the zooplankton community with environmental conditions, and particularly the greater abundance of larger taxa in association with hypoxia, has implications for the contribution of zooplankton-mediated vertical flux to oxygen drawdown, and for the quality of the food environment for larval and other planktivorous fish.
TL;DR: It is demonstrated that qPCR analysis of prey DNA in copepod guts can be used to provide a quantitative index of feeding rates, and that prey 18S rDNA could be detected routinely and quantified in the guts and fecal pellets of A. tonsa.
Abstract: Copepod feeding and digestion rates were measured using quantitative polymerase chain reaction (qPCR) to amplify the prey Thalassiosira weissflogii and Heterocapsa triquetra from the guts of Acartia tonsa. Using species-specific primers, prey 18S rDNA could be detected routinely and quantified in the guts and fecal pellets of A. tonsa. Recovery of gut contents DNA using two fixation methods was compared. Prey 18S copy numbers were .10-fold higher in copepods fixed in 95% ethanol (3260+ 822 copies copepod) compared with anesthetized and frozen copepods (210+ 19 copies copepod). Experiments using 95% ethanol fixation showed rapid prey DNA digestion rates during the initial 2 min after ingestion (0.7 min) after which they slowed 10-fold. Chlorophyll pigment disappearance rates were slower ( 0.015 min). Rates of gut filling measured by DNA and gut pigments differed, reaching 95% of the asymptote, Imax, in 3 and 58 min, respectively, likely reflecting differences in rates at which biomarkers were digested. Gut fullness measured by DNA increased with prey concentration, reaching Imax at 9760 copies copepod and a critical concentration (Icrit) at 1530 cells mL . These results demonstrate that qPCR analysis of prey DNA in copepod guts can be used to provide a quantitative index of feeding rates.
TL;DR: The doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea), a zooplankton species abundant in the Gulf of Mexico, was observed to ingest dispersed oil droplets (1 -30 mm in diameter), produced by vigorous mixing of a dispersant with crude oil as discussed by the authors.
Abstract: Subsurface plumes of small, stable dispersed oil droplets are a feature of oil spills treated with dispersants. The doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea), a zooplankton species abundant in the Gulf of Mexico, was observed to ingest dispersed oil droplets (1 – 30 mm in diameter), produced by vigorous mixing of a dispersant with crude oil. Oil droplets were first observed in the doliolid stomach, followed by appearance in the fecal pellets formed within the doliolid. Released fecal pellets had numerous oil droplets. Concentrations of ingested oil droplets in doliolids, exposed to high droplet concentrations (17 000 droplets/mL), increased from 800 to 5300 droplets/doliolid after 4 and 24 h, respectively. At a lower concentration (1200 droplets/mL), the ingested droplet concentration after 12 h was 450 droplets/doliolid. Fecal pellets were an important route for the elimination of oil droplets. Oil droplet concentrations in fecal pellets were 85 droplets/ fecal pellet and 10 droplets/fecal pellet at high and low concentrations of dispersed oil, respectively. A calculation of the amount of oil in doliolid fecal pellets, based on doliolid concentrations, their fecal production rates and oil concentration in the fecal pellets, indicated that 200 mg oil/m 3 -day could be carried to the
TL;DR: In this article, MapS and Runge discuss the role of the ocean environment in the development of marine biology and its role in the discovery of the first sea-plane propulsion system.
Abstract: FREDERIC MAPS1,2*, JEFFREY A. RUNGE1,2, ANDREW LEISING3, ANDREW J. PERSHING1,2, NICHOLAS R. RECORD1,2, STEPHANE PLOURDE4 AND JAMES J. PIERSON5 1 SCHOOL OF MARINE SCIENCES, UNIVERSITY OF MAINE, ORONO, ME 04469, USA, GULF OF MAINE RESEARCH INSTITUTE, 350 COMMERCIAL ST., PORTLAND, ME 04101, USA, NOAA-SWFSC, ENVIRONMENTAL RESEARCH DIVISION, 1352 LIGHTHOUSE AVE., PACIFIC GROVE, CA 93950, USA, MAURICE-LAMONTAGNE INSTITUTE, FISHERIES AND OCEANS CANADA, 850 ROUTE DE LA MER, C.P. 1000, MONT-JOLI, QC, CANADA G5H 3Z4 AND HORN POINT LABORATORY, UNIVERSITY OF MARYLAND CENTER FOR ENVIRONMENTAL SCIENCE, 2020 HORNS POINT RD., CAMBRIDGE, MD 21613, USA
TL;DR: In this paper, the authors identify the significance of these environmental factors for controlling the species-specific biomass distribution and the nature of such relationships and conclude that C. hyperboreus is an expatriate to the study area.
Abstract: The biomass of Calanus spp. in the Norwegian Atlantic Current and the West Spitsbergen Current (2001–2009) was statistically related to a combination of salinity, temperature, water depth and sea ice concentration. The aim of this study was to identify the significance of these environmental factors for controlling the species-specific biomass distribution and the nature of such relationships. Calanus finmarchicus dominated the entire area and its biomass was mainly related to salinity. Calanus glacialis was mainly found along the northwest shelf of the Barents Sea, but its biomass was also related to the sea ice concentration and temperature with a critical threshold 68C, above which the presence and biomass of C. glacialis decreased. The Calanus hyperboreus biomass was related to all environmental factors, which characterized by a confined spatial distribution to water associated with the Greenland Sea Gyre. We conclude that C. hyperboreus is an expatriate to the study area. The Calanus biomass distribution will not change greatly in the study area with an expected increase of water temperature by 28C, whereas the critical temperature threshold for C. glacialis will be exceeded with temperature increases of 48C with a likely disappearance of this cold water species from the north-west shelf of the Barents Sea.
TL;DR: It is suggested that cyanobacterial blooms may change competitive relations of small-sized cladocerans and copepoda, favoring small cladocerrans (except larger genera) in crustacean zooplankton communities.
Abstract: To assess the effect of Microcystis blooms on the crustacean zooplankton community, we conducted a large-scale monthly survey from 2008 to 2010 in Lake Taihu, China. During the sampling period, Microcystis was the dominant genus in the phytoplankton community (79 of total biomass), while the crustacean zooplankton community was dominated by small-sized cladocerans (primarily Bosmina coregoni and Ceriodaphnia cornuta) and copepods. During the study, plankton exhibited significant spatial heterogeneity. The northern and western regions suffered from harmful Microcystis blooms and had higher cladoceran production. In the eastern region where Microcystis blooms seldom occurred, copepods accounted for a relatively larger proportion. Both stepwise multiple linear regression and redundancy analysis demonstrated that Microcystis was the most important factor controlling the spatial dynamics of zooplankton. Linear regression analysis revealed that both cladocera and copepoda were positively correlated with Microcystis and the response of cladocerans (R-2 0.73, P 0.001) to Microcystis was stronger than that of copepods (R-2 0.44, P 0.001). Our study suggested that cyanobacterial blooms may change competitive relations of small-sized cladocerans and copepoda, favoring small cladocerans (except larger genera).
TL;DR: A bimonthly monitoring of P. noctiluca surface density from a sailboat along a 35-km coastal to offshore transect in the Ligurian Sea between February and October 2011 suggests that outbreaks observed on Mediterranean shores may result from the transport of the permanent offshore population inshore by specific hydrodynamic conditions.
Abstract: The scyphozoan Pelagia noctiluca reproduces by direct development without a benthic stage. Typically, this jellyfish is found offshore with a holoplanktonic lifecycle, vertical migration and feeding behaviours. Frequent outbreaks have been well documented on the Mediterranean shores since the 19th century; however, the offshore distribution of this species remains mostly unknown. In this study, we performed a bimonthly monitoring of P. noctiluca surface density, at high resolution, from a sailboat, along a 35-km coastal to offshore transect in the Ligurian Sea, between February and October 2011. During daylight, P. noctiluca was rarely seen. At night, offshore, P. noctiluca was always present, while within 5 km of the coast, P. noctiluca was rarely observed. Pelagia noctiluca aggregations were most abundant within the Northern Current of the Ligurian Sea. Our findings suggest that P. noctiluca outbreaks observed on Mediterranean shores may result from the transport of the permanent offshore population inshore by specific hydrodynamic conditions.
TL;DR: In this article, the authors used CTD and zooplankton stations to determine the three-dimensional distribution of larval fish assemblages in an anticyclonic eddy in the southern Gulf of California during 2007.
Abstract: Transects of CTD (to 1000 m) and zooplankton stations (to 200 m in 50 m strata) were made across an anticyclonic eddy in the southern Gulf of California during October 2007 to determine its influence upon the three-dimensional distribution of larval fish assemblages. The eddy was 90 km in diameter and 70 m deep. A larval fish assemblage, representing a mix of oceanic and coastal species, was defined mainly in the eddy from 200 m depth to the surface. Mesopelagic species, such as Vinciguerria lucetia, were dominant. Coastal reef (Diplectrum sp.) and pelagic (Auxis spp.) species were found mainly in the surface layer. This suggests that, because of the Gulf ’s relative narrowness, the eddy trapped coastal fish larvae during its formation and trajectory southward, retaining larvae of different adult habits. Another larval fish assemblage was defined off the eastern coast; its high larval abundance and specific richness was probably associated with coastal upwelling. Mesopelagic species (e.g. Triphoturus mexicanus) dominated this assemblage, and coastal demersal species that were absent from the eddy (e.g. Symphurus williamsi) were recorded in the surface layer, suggesting that the thermocline was a vertical boundary in this assemblage. The 3D differentiation of planktonic habitats was the result of the mesoscale hydrodynamics in the area sampled, in particular that associated to the eddy life history and characteristics (radius, depth and velocity), and to coastal upwelling, promoting larval retention of a mix of species of different adult habits.
TL;DR: The sea ice diatom biomarker IP25 has been detected and quantified in bulk zooplankton obtained from the Amundsen Gulf (Canada) in 2008.
Abstract: The sea ice diatom biomarker IP25 has been detected and quantified in bulk zooplankton obtained from the Amundsen Gulf (Canada) in 2008 This study represents the first example of the detection of this biomarker in the pelagic food web Concentrations of IP25 ranged from 5 to 15 ng g dry weight with peak values occurring broadly at the same time as those found for this biomarker in sea ice samples determined previously from the same region; a 25–30 day lag between the sea ice bloom and zooplankton IP25 profiles is interpreted in terms of a predator–prey relationship IP25 concentrations in zooplankton declined towards the end of the spring sea ice algal bloom and during the main period of ice melt At this point, concentrations of n-C21:6, a common biomarker of general marine diatoms, increased substantially in the zooplankton, indicative of a switch in feeding patterns This detection of IP25 in one of the first trophic levels of the Arctic marine ecosystem has potentially important implications for the investigation of polar food webs and the impacts that changes to sea ice conditions will have on these
TL;DR: It is argued that predation pressure by the now nearly extinct baleen whales was an important driving force in the evolution of life history diversity in the Arctic Calanus complex.
Abstract: Before man hunted the large baleen whales to near extinction by the end of the nineteenth century, Arctic ecosystems were strongly influenced by these large predators. Their main prey were zooplankton, among which the calanoid copepod species of the genus Calanus, long considered key elements of polar marine ecosystems, are particularly abundant. These herbivorous zooplankters display a range of adaptations to the highly seasonal environments of the polar oceans, most notably extensive energy reserves and seasonal migrations to deep waters where the non-feeding season is spent in diapause. Classical work in marine ecology has suggested that slow growth, long lifespan and large body size in zooplankton are specific adaptations to life in cold waters with short and unpredictable feeding seasons. Here, we challenge this understanding and, by using an analogy from the evolutionary and contemporary history of the avocado, argue that predation pressure by the now nearly extinct baleen whales was an important driving force in the evolution of life history diversity in the Arctic Calanus complex.
TL;DR: The use of the new fingerprint recorded for P. globosa improved the detection of Isochrysis sp .T his suggests the possibility of using the FluoroProbe to monitor Haptophytes other than P. Globosa by calibrating the device with species representative of the region of interest.
Abstract: In this study, we examined the possibility of using the FluoroProbe for monitoring the dynamics of the Haptophyte Phaeocystis globosa in the coastal waters of the eastern English Channel. The FluoroProbe was recalibrated by recording a new fingerprint for P. globosa and the use of this new fingerprint was tested through a series of laboratory and in situ experiments. The annual dynamics of P. globosa estimated using the FluoroProbe and by flow cytometry were similar. A strong relationship was found between the FluoroProbe estimates of P. globosa biomass expressed in terms of chlorophyll a equivalent per litre (eq. m gL 21 ) and flow cytometric cell counts (r ¼ 0.889, P , 0.001, n ¼ 121). The FluoroProbe can be used to detect the flagellated cells as well as the colonial cells of P. globosa but not to distinguish these two cell types in mixed assemblages. The use of the new fingerprint recorded for P. globosa improved the detection of Isochrysis sp .T his suggests the possibility of using the FluoroProbe to monitor Haptophytes other than P. globosa by calibrating the device with species representative of the region of interest. However, it is important to note that the detection of P. globosa at the species level was possible in the eastern English Channel because it was the only Haptophyte species present with a biomass sufficient to be detected by the FluoroProbe. In areas where several Haptophyte species are simultaneously present, their discrimination will be impossible and in such situations the FluoroProbe can be used to monitor the dynamics of the combined Haptophyte group.
TL;DR: Comparisons of mesozooplankton abundance and species composition in the upper 200 m at seven sites in Lutzow-Holm Bay, Antarctica, were compared using plankton nets with 60, 100 or 330 mm mesh during the austral summer of 2007-2008 found no significant underestimation of abundance using the 100 mm mesh.
Abstract: Mesozooplankton abundance and species composition in the upper 200 m at seven sites in Lutzow-Holm Bay, Antarctica, were compared using plankton nets with 60, 100 or 330 mm mesh during the austral summer of 2007-2008. While the collection efficiency of the 330 mm mesh was low, ranging from 2.0 to 5.6%, owing to the significant underestimation of small copepod species, no significant underestimation of abundance was found using the 100 mm mesh, except for copepod nauplii.
TL;DR: Diversity and structure of ciliate communities in the Neva Estuary (Baltic Sea) were studied at two near-shore stations from October 2007 to January 2009, with an unusual winter peak of the ciliate Trithigmostoma sp.
Abstract: Diversity and structure of ciliate communities in the Neva Estuary (Baltic Sea) were studied at two near-shore stations from October 2007 to January 2009. Ciliates from 111 taxa were detected, including new records of 24 species for the Baltic Sea. The ciliate taxa were grouped into size-categories and trophic guilds and their species composition, abundance and biomass were monitored in different seasons. Two distinct associations replaced each other during seasonal succession at water temperatures 5–128C. During the warm season (late April–October) ciliate communities were composed essentially of picoand nano-filterers (mostly algivorous) that became less important in the cold season (October–early April). The predator, Monodinium balbiani, and bactivorous peritrichs were characteristic of the warm season, while in the cold season, other predatory (Lacrymaria coronata group) and bactivorous (Cyclidium spp., Aspidisca sp., Chilodonella sp.) ciliates occurred. The most abundant size groups were small ciliates (20–30 mm) and nanociliates (,20 mm). A proportion of large ciliates (.60 mm) increased in the cold season due to the appearance of benthic species in the plankton. Total ciliate abundance and biomass ranged 0.12–10.3 10 ind L and 0.3– 53.3 mg C L, respectively. An unusual winter peak of the ciliate Trithigmostoma sp. was observed (32.8 mg C L) although generally the overall ciliate numbers decreased in the cold season.
TL;DR: In this paper, the authors investigated the relationship between the spring phytoplankton community and environmental factors in the Brazil-Malvinas confluence region and determined the community composition by the high performance liquid chromatography/CHEMTAX approach, complemented with microscopic examination.
Abstract: This study investigates the relationships between the spring phytoplankton community and environmental factors in the Brazil-Malvinas confluence region. Phytoplankton community composition was determined by the high performance liquid chromatography/CHEMTAX approach, complemented with microscopic examination. Abiotic factors included temperature, salinity, dissolved inorganic macronutrients (ammonium, nitrite, nitrate, phosphate and silicate), water column stability and upper mixed layer depth (UMLD). These environmental variables were reasonably informative to explain the variability of the phytoplankton communities (44% of variation explained). Cluster and canonical correspondence analyses allowed discrimination of four zones (coastal, Sub-Antarctic, tropical and intermediate zones), also identifiable in the T–S diagrams and in the nutrient spatial distribution patterns. The presence of nutrient-rich Sub-Antarctic waters was a major oceanographic feature, associated with diatoms and dinoflagellates. However, in the Sub-Antarctic zone, biomass was particularly low, probably as a result of grazing pressure, as suggested by chemical and biological indicators. In contrast, in oligotrophic tropical waters, phytoplankton was mainly composed by small nanoflagellates and cyanobacteria. A large intermediate zone was also dominated by nanoflagellates, mainly Phaeocystis antarctica, probably favored by strong water column stability. The coastal zone exhibited fairly similar conditions to those in the intermediate zone, but with deeper UMLD, a favorable condition for diatom growth. These results emphasize the importance of the properties of water masses and also biological processes such as grazing in structuring phytoplankton communities in the region.
TL;DR: It is suggested that flow cytometric measurement of the depolarization forward scattered light using a Brewster's Window Analyzer can be used to quantify the degree of calcification of coccolithophores at the single-cell level, and provides a potentially valuable method for analysis of calcifying state of individual cells.
Abstract: Coccolithophores are important primary producers and a dominant group of calcifying organisms in the ocean. Calcification state depends on genetic, physiological and environmental factors. We show that flow cytometric measurement of the depolarization forward scattered light using a Brewster's Window Analyzer can be used to quantify the degree of calcification of coccolithophores at the single-cell level. Calcite-containing particles or cells were distinguished from non-calcified particles or cells by high values of forward scatter light with polarization orthogonal to that of the laser. Forward scatter polarization state varied strongly and linearly with the number of attached coccoliths per coccosphere when Emiliania huxleyi cells were first completely decalcified and then allowed to rebuild coccospheres. Cells of the heavily calcified E. huxleyi R-morphotype strain NZEH were also grown in different extracellular Ca2+ concentrations, forming complete coccospheres that contained similar numbers of attached coccoliths but varied in total calcite mass. Forward scatter polarization state varied strongly and linearly with coccosphere calcite mass. In contrast, forward scatter polarization state of detached coccoliths did not vary significantly with calcite weight, although forward scatter and side scatter did. Treatments had relatively minor effects on forward scatter, side scatter and forward scatter polarization state of decalcified cells, suggesting that depolarization of forward scatter light from E. huxleyi cells might be linearly determined, to a first approximation, by the ratio of surface calcite to organic protoplast. We suggest that flow cytometric measurement of forward scatter depolarization provides a potentially valuable method for analysis of calcification state of individual cells.