Planktonic Assemblages Research Articles

On the issue of influence of coastal seabird colonies on adjacent pelagic communities of the Kola Peninsula

According to previously obtained data, seabird colonies, as a biotic factor, exert a substantial influence on communities of some coastal waters around the Novaya Zemlya archipelago. In the current study, an attempt has been made to assess the degree of the impact of seabird colonies on planktonic assemblages in the coastal waters of the Kola Peninsula. A study of phyto- and zooplankton near the colony on Cape Gorodetsky (Rybachy Peninsula) did not reveal any substantial differences in the qualitative and quantitative composition of this community in comparison with the other coastal waters of the Barents Sea. The lack of influence on the coastal biota can be explained by the low abundance of birds in the colonies, as well as by the effect of the Murman Coastal Current, which carries away and disperses the biogenic matter that enters the aquatic environment with guano.

Interspecies Interactions Reverse the Hazard of Antibiotics Exposure: A Plankton Community Study on Responses to Ciprofloxacin hydrochloride

The ecotoxicological effects of Ciprofloxacin hydrochloride (CIP) were tested on population densities of plankton assemblages consisting of two algae (Isochrysis galbana and Platymonas subcordiformis) and a rotifer (Brachionus plicatilis). The I. galbana showed a significant decrease in densities when concentrations of CIP were above 2.0 mg L−1 in single-species tests, while P. subcordiformis and B. plicatilis were stable in densities when CIP were less than10.0 mg L−1. The equilibrium densities of I. galbana in community test increased with CIP concentrations after falling to a trough at 5.0 mg L−1, showed a completely different pattern of P. subcordiformis which decreased with CIP concentrations after reaching a peak at 30.0 mg L−1. The observed beneficial effect was a result of interspecies interactions of trophic cascade that buffered for more severe direct effects of toxicants. The community test-based NOEC of CIP (2.0 mg L−1), embodying the indirect effects, was different from the extrapolated one derived by single-species tests (0.5 mg L−1), but all lacked confidence interval. A CIP threshold concentration of obvious relevance to ecological interaction was calculated with a simplified plankton ecological model, achieving a value of 1.26 mg L−1 with a 95% bootstrapping confidence interval from 1.18 to 1.31 mg L−1.

Foraminíferos planctônicos e bentônicos cretáceos da Ilha de Quiepe, Formação Algodões, Bacia de Camamu, Bahia, Brasil

A sampling program from Camamu Bay and its neighborhood were undertaken to microfossils appraisal of the Algodoes Formation outcrops, Camamu Basin. Among the basins of the Brazilian eastern margin, the Camamu Basin is the least known. This study aimed to identify planktonic and benthonic foraminifera of the Algodoes Formation, Camamu Basin, and to make biostratigraphic, paleoecological and paleobiogeographic inferences based on the microfauna. The sampling points were located at the Boipeba Island (Boipeba and Tassimirim beaches), and at the Camamu Bay (Barra Grande and Taipus de Fora beaches; Quiepe and Cangaiba islands). In total, 50 rock samples were collected, constituted in great part of calcarenites, besides dolomites, calcilutites and calcareous shale. All the material was subjected to a three laboratory techniques, applied to recover or observe carbonate microfossils: thin section, acetolysis and hydrogen peroxide methods. Only five samples from Quiepe Island showed results. Planktonic foraminifera, belonging to the genus Whiteinella (W. aff. aprica, W. archaeocretacea, W. baltica and Whiteinella sp. 1) were identified, besides scarce specimens assigned to Hedbergella (Hedbergella ? sp.1). The paleoecological studies, based on the benthonic foraminifera, revealed predominance of calcareous specimens (Bolivinidae ?), followed by agglutinated taxa (Spiroplectamminidae ? and Textulariidae ?). The occurrence of W. aff. aprica, W. archaeocretacea and W. baltica in the planktonic assemblage suggests a upper Cenomanian to upper Turonian age for the studied section of the Algodoes Formation. However, the correlation with ammonites data (Mammites, Kamerunoceras, Romaniceras and Neoptychites) allows to a better biostratigraphic resolution, indicating strata of early-middle Turonian age. The benthonic foraminifera observed (Bolivinidae ?, Spiroplectamminidae ? and Textulariidae?) indicated the predominance of infaunal organisms that lived on substrates constituted by calcareous mud preferably, and probably occupied the middle-deep neritic paleobathymetric range. The finding of Whiteinella (W. aff. aprica, W. archaeocretacea, W. baltica, Whiteinella sp. 1), besides the ostracod specimens of the Sapucariella ex gr. sapucariensis are important biogeographical records in the upper Cretaceous of South America and Africa.

Trace metal composition of size‐fractionated plankton in the Western Philippine Sea: The impact of anthropogenic aerosol deposition

AbstractThe surface water of the Western Philippine Sea (WPS) receives a significant amount of anthropogenic aerosols from East Asia, serving as an ideal location to investigate the impact of anthropogenic aerosol deposition on trace metal composition and cycling in the Northwestern Pacific Ocean (NWPO). As part of the Taiwan GEOTRACES process study, we have collected size‐fractionated plankton from surface water to investigate their metal composition in the open ocean. Elemental ratios in plankton, P‐ and Al‐normalized, are used to evaluate the sources of trace metals and the relative contribution of different metal components in plankton assemblages. Most of the trace metal quotas in plankton are one to two orders of magnitude higher than their intracellular plankton quota, indicating that the majority of the metals are most likely to be extracellularly adsorbed or aggregated on plankton. The metal to Al ratios for most of the trace metals in plankton are also one to two orders of magnitude higher than their lithogenic composition, but are relatively close to metal composition in aerosols collected in situ. This supports the notion that particulate trace metals associated with plankton mainly originate from anthropogenic aerosols, not lithogenic particles. Compared to plankton metal quotas obtained in other oceanic regions, trace metal quotas observed in the WPS rank among the highest for Fe, Mn, Zn, and Cu globally. Our study demonstrates that anthropogenic aerosol deposition has significantly elevated trace metal concentrations in the size‐fractionated plankton in the surface water of the NWPO relative to the biological requirements.

Influence of ocean acidification on plankton community structure during a winter-to-summer succession: An imaging approach indicates that copepods can benefit from elevated CO2 via indirect food web effects.

Plankton communities play a key role in the marine food web and are expected to be highly sensitive to ongoing environmental change. Oceanic uptake of anthropogenic carbon dioxide (CO2) causes pronounced shifts in marine carbonate chemistry and a decrease in seawater pH. These changes–summarized by the term ocean acidification (OA)–can significantly affect the physiology of planktonic organisms. However, studies on the response of entire plankton communities to OA, which also include indirect effects via food-web interactions, are still relatively rare. Thus, it is presently unclear how OA could affect the functioning of entire ecosystems and biogeochemical element cycles. In this study, we report from a long-term in situ mesocosm experiment, where we investigated the response of natural plankton communities in temperate waters (Gullmarfjord, Sweden) to elevated CO2 concentrations and OA as expected for the end of the century (~760 μatm pCO2). Based on a plankton-imaging approach, we examined size structure, community composition and food web characteristics of the whole plankton assemblage, ranging from picoplankton to mesozooplankton, during an entire winter-to-summer succession. The plankton imaging system revealed pronounced temporal changes in the size structure of the copepod community over the course of the plankton bloom. The observed shift towards smaller individuals resulted in an overall decrease of copepod biomass by 25%, despite increasing numerical abundances. Furthermore, we observed distinct effects of elevated CO2 on biomass and size structure of the entire plankton community. Notably, the biomass of copepods, dominated by Pseudocalanus acuspes, displayed a tendency towards elevated biomass by up to 30–40% under simulated ocean acidification. This effect was significant for certain copepod size classes and was most likely driven by CO2-stimulated responses of primary producers and a complex interplay of trophic interactions that allowed this CO2 effect to propagate up the food web. Such OA-induced shifts in plankton community structure could have far-reaching consequences for food-web interactions, biomass transfer to higher trophic levels and biogeochemical cycling of marine ecosystems.

Optode use to evaluate microbial planktonic respiration in oligotrophic ecosystems as an indicator of environmental stress

The suitability of O2 optodes to resolve the effects of global-change stressors on respiration of microbial planktonic assemblages from oligotrophic ecosystems was tested. With this aim, we first evaluated how O2 measurements with optodes on closed flasks depended on delayed temperature equilibration (hysteresis), which can bias actual measurements on samples not subjected to constant temperature. This must be addressed when using optodes for in situ measurements. Thus, we provide the mathematical tools to correct the effects of hysteresis on O2 measurements hence removing the constraints of maintaining a constant temperature over the long incubations required to measure respiration in oligotrophic ecosystems. Optodes proved suitable to resolve the effects of stressors such as CO2, temperature, thermal stratification, nutrient input, and ultraviolet radiation in different oligotrophic aquatic ecosystems. These experiments resulted in significant differences in microbial planktonic respiration for all stressors tested. From these results, we conclude that (1) optodes constitute a useful tool to make realistic measurements on samples subjected to natural (or experimental) ranges of temperature variability, and (2) microbial planktonic respiration measured with O2 optodes has the potential to be used as an ecological indicator for assessing the effects of environmental stress, even in oligotrophic aquatic ecosystems, where higher sensitivities are needed.

Impact of water input on plankton temporal dynamics from a managed shallow saline lake

La Salada is a shallow saline lake located in the SW of the Pampas subject to significant water management, so the primary objective was to assess whether the water input and physicochemical parameters have an impact on the plankton assemblages over a two year period (2013–dry and 2014–wet). The plankton community structure and physicochemical variables showed substantial changes over the study period. La Salada hosted a plankton community characterized by low diversity and small sized organisms. The nanoplanktonic fraction organisms (2–20 μm) dominate the phytoplankton community. Ochromonas sp. showed the maximum abundance throughout the whole study period. The zooplankton community was dominated by rotifers, with a lack of cladocerans. Halotolerant species, e.g. the rotifer Brachionus plicatilis and the cyclopod Apocyclops sp. were the main species. The seasonal temperature and conductivity dynamics influence the plankton abundance dynamics in La Salada. The increment of nutrients and decrease of conductivity caused by the water input led to an increase in plankton biomass and shaped its composition. These findings emphasize that interactions between plankton, salinity, and nutrients are sensitive to the water input and they improve the understanding of the impact of adequate management decisions.

Evaluation of Spatial-Temporal Variations of Water Quality and Plankton Assemblages and Its Relationship to Water Use in Kulekhani Multipurpose Reservoir, Nepal

Spatial and temporal variation in planktons and water quality parameters were investigated in order to determine the effects of seasonal water use on reservoir water quality and planktons’ diversity in Kulekhani Multipurpose Reservoir, Nepal. This study also focuses on interactions among various water quality parameters with planktons and how such interactions can affect the second major utility, the fish farming in the reservoir. The analyses of seasonal water samples collected from three different sampling locations in the reservoir showed that select water quality parameters varied significantly (P < 0.05) with sampling seasons (transparency: 30 - 250 cm, pH: 7 - 7.5, alkalinity: 30 - 120 mg/L, DO: 6 - 11.5 mg/L, CO2: 0.1 - 1.1 mg/L) and sampling locations (phosphate: 0.1 - 0.25 mg/L, nitrate 0.01 - 0.19 mg/L) in the reservoir. Three groups of zooplankton and four classes of phytoplankton, respectively with eleven and twelve genera, were identified and quantified in the reservoir. Among them, Cyclops, Asplanchana, and Keratella were most dominant zooplanktons while Synedra, Melosira and Peridinum were the most dominant phytoplankton in the reservoir water. The abundance of select zooplanktons (Cyclops, Keratella, Polyanthra), and phytoplankton (Navicula, Melosira, Amphora, Chroococcus, Staurastrum, Scendesmus) showed significant interaction between sampling sites and sampling seasons, while the other varied only with sampling seasons and/or sites. These results showed that seasonal water level fluctuations, along with the variation of water quality parameters, change the abundance and diversity of planktons’ in the reservoir. Such changes can negatively impact the fish in cage culture, affecting the livelihood of people extensively relying on these fish farming.

Metabarcoding and metabolome analyses of copepod grazing reveal feeding preference and linkage to metabolite classes in dynamic microbial plankton communities.

In order to characterize copepod feeding in relation to microbial plankton community dynamics, we combined metabarcoding and metabolome analyses during a 22-day seawater mesocosm experiment. Nutrient amendment of mesocosms promoted the development of haptophyte (Phaeocystis pouchetii)- and diatom (Skeletonema marinoi)-dominated plankton communities in mesocosms, in which Calanus sp. copepods were incubated for 24h in flow-through chambers to allow access to prey particles (<500μm). Copepods and mesocosm water sampled six times spanning the experiment were analysed using metabarcoding, while intracellular metabolite profiles of mesocosm plankton communities were generated for all experimental days. Taxon-specific metabarcoding ratios (ratio of consumed prey to available prey in the surrounding seawater) revealed diverse and dynamic copepod feeding selection, with positive selection on large diatoms, heterotrophic nanoflagellates and fungi, while smaller phytoplankton, including P.pouchetii, were passively consumed or even negatively selected according to our indicator. Our analysis of the relationship between Calanus grazing ratios and intracellular metabolite profiles indicates the importance of carbohydrates and lipids in plankton succession and copepod-prey interactions. This molecular characterization of Calanus sp. grazing therefore provides new evidence for selective feeding in mixed plankton assemblages and corroborates previous findings that copepod grazing may be coupled to the developmental and metabolic stage of the entire prey community rather than to individual prey abundances.

Environmental perturbations at the early Eocene ETM2, H2, and I1 events as inferred by Tethyan calcareous plankton (Terche section, northeastern Italy)

AbstractSeveral early Eocene hyperthermals have been recently investigated and characterized in terms of temperature anomalies and oceanographic changes. The effects of these climatic perturbations on biotic communities are much less constrained. Here we present new records from the Terche section (northeastern Italy) that, for the first time, integrates data on planktic foraminifera and calcareous nannofossils across three post‐Paleocene‐Eocene Thermal Maximum negative carbon isotope excursions (CIEs). The biomagnetostratigraphic framework generated at Terche allows us to confidently relate such CIEs to the Eocene Thermal Maximum 2 (ETM2), H2, and I1 events. Each of these events coincides with lithological anomalies characterized by significantly lower calcium carbonate content (marly units, MUs). We interpret these MUs as mainly linked to an effect of increased terrigenous dilution, as dissolution proxies do not display significant variations. Calcareous plankton assemblages change significantly across these events and radiolarians increase. Observed changes suggest that transient warming and environmental perturbations, though more intense during ETM2, occurred during each of the three investigated perturbations. Variations among calcareous plankton suggest increase in surface‐water eutrophication with respect to the pre‐event conditions, coupled with a weakening of the upper water‐column thermal stratification. Higher nutrient discharge was related to intensification of the hydrological cycle as a consequence of the warmer climate. These conditions persisted during the early CIE recovery, implying slower recovery rates for the environment and biota than for the carbon cycle.

Ecological response to hydrological variability and catchment development: Insights from a shallow oxbow lake in Lower Mississippi Valley, Arkansas

The ecological response of shallow oxbow lakes to variability in hydrology and catchment development in large river floodplain ecosystems (RFE) in Arkansas remains largely unknown. Investigating these responses will advance our understanding of ecological evolution of oxbow lakes in response to the major environmental drivers, which will establish baseline conditions required to develop effective management practices for RFE.In this pilot study, we examined the potential of using a dated surface sediment core from Adams Bayou, a floodplain lake located within the Cache-Lower White River Ramsar site in SE Arkansas. Stratigraphic records of diatoms and sediment geochemistry were used to ascertain variation in Adams Bayou's ecological condition. During 1968–2008, in response to hydrological and anthropogenic changes, Adams Bayou's diatom assemblages progressed from predominantly benthic (Gomphonema parvulum and Meridion circulare) to primarily planktonic assemblage (Aulacoseira granulata and Cyclotella meneghiniana), along with a decrease in magnetic susceptibility (k) and % silt. Statistical analyses reveled that during 1968–2000, higher hydrological connectivity and catchment alterations drove Adams Bayou's ecosystem. After 2000, lower hydrological connectivity and increase in cultivation were the major drivers. The potential impact of increasing air temperature was also noted.The shift in Adams Bayou from a connected, clear, mesotrophic state to a relatively isolated, turbid and nutrient enriched state is consistent with regime shift models and highlights its sensitivity to a combination of environmental stresses prevalent in the catchment. Although fluvial systems pose challenges in establishing clear chronologies, oxbow lake sediments can be a effective paleoecological archives. Our work provides clear evidence for the change in the ecological character of this wetland of international significance and flags the need for a wider assessment of water bodies across this site under obligations to the Ramsar Convention.

No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community

Abstract. Nitrogen fixation by filamentous cyanobacteria supplies significant amounts of new nitrogen (N) to the Baltic Sea. This balances N loss processes such as denitrification and anammox, and forms an important N source supporting primary and secondary production in N-limited post-spring bloom plankton communities. Laboratory studies suggest that filamentous diazotrophic cyanobacteria growth and N2-fixation rates are sensitive to ocean acidification, with potential implications for new N supply to the Baltic Sea. In this study, our aim was to assess the effect of ocean acidification on diazotroph growth and activity as well as the contribution of diazotrophically fixed N to N supply in a natural plankton assemblage. We enclosed a natural plankton community in a summer season in the Baltic Sea near the entrance to the Gulf of Finland in six large-scale mesocosms (volume ∼ 55 m3) and manipulated fCO2 over a range relevant for projected ocean acidification by the end of this century (average treatment fCO2: 365–1231 µatm). The direct response of diazotroph growth and activity was followed in the mesocosms over a 47 day study period during N-limited growth in the summer plankton community. Diazotrophic filamentous cyanobacteria abundance throughout the study period and N2-fixation rates (determined only until day 21 due to subsequent use of contaminated commercial 15N-N2 gas stocks) remained low. Thus estimated new N inputs from diazotrophy were too low to relieve N limitation and stimulate a summer phytoplankton bloom. Instead, regeneration of organic N sources likely sustained growth in the plankton community. We could not detect significant CO2-related differences in neither inorganic nor organic N pool sizes, or particulate matter N : P stoichiometry. Additionally, no significant effect of elevated CO2 on diazotroph activity was observed. Therefore, ocean acidification had no observable impact on N cycling or biogeochemistry in this N-limited, post-spring bloom plankton assemblage in the Baltic Sea.

Sea surface water variability during the Mid-Brunhes inferred from calcareous plankton in the western Mediterranean (ODP Site 975)

Planktonic foraminifera and calcareous nannoplankton were analyzed in core Ocean Drilling Program Site 975, located in the western Mediterranean, in order to study their response to environmental changes across the Mid-Brunhes interval and specifically through Marine Isotope Stage (MIS) 15 and 8 (ca. 650–230ka). Multivariate analysis of assemblage composition revealed that the calcareous plankton dynamics were mainly driven by surface water temperatures both on glacial-interglacial and stadial-interstadial time scales. Throughout the studied interval, foraminiferal and nannoplankton assemblages responded to environmental forcing in concert, except during MIS 15, when multiple environmental factors appear to have been superimposed on the otherwise dominating effect of temperature variability. Sea surface temperature (SST) has been estimated from planktonic foraminiferal assemblages using the artificial neural networks method pointing out relevant seasonal variations through the record. Our reconstructions reveal that calcareous plankton assemblages also responded to other environmental factors than temperature, including modification in surface water stratification, nutrient availability and detrital input. Specifically, a more stable, stratified water column seems to have accompanied the interval through MIS 15–13. On the other hand, across the Mid-Brunhes interval, from MIS 12 onwards, the enhanced glacial strength affected both planktonic foraminifera and calcareous nannofossils: planktonic foraminifera indicate that mixed and productive surface waters developed during glacials and stadials, accompanied by episodes of increased detrital input as suggested by calcareous nannoplankton assemblages. Enhanced food availability was likely driven by wind-induced upwelling and/or by continental coastal input during dry conditions persisting in the Mediterranean region and over North Africa. Finally, spectral and wavelet analyses of calcareous plankton time series allowed to identify the pattern of periodic response of the plankton at Milankovitch cycles and, in some cases, at millennial variability. The dominant 100kyr periodicity recorded in surface water temperature proxies clearly reflects a major response of the planktonic community to the global glacial-interglacial climate pattern. High-frequency variation (~5–8, ~11–13ky) of surface water temperature proxies and of selected taxa abundance highlights the occurrence of millennial-scale instability superimposed on the paleoenvironmental modifications occurring through the Mid-Brunhes interval climate transition. This framework accounts for the occurrence of different surface water dynamics across the Mid-Brunhes interval and is in favor of the hypothesis that the millennial scale surface water temperature variations are modulated by the harmonics of the precession forcing.

Ocean acidification reduces transfer of essential biomolecules in a natural plankton community.

Ocean acidification (OA), a process of increasing seawater acidity caused by the uptake of anthropogenic carbon dioxide (CO2) by the ocean, is expected to change surface ocean pH to levels unprecedented for millions of years, affecting marine food web structures and trophic interactions. Using an in situ mesocosm approach we investigated effects of OA on community composition and trophic transfer of essential fatty acids (FA) in a natural plankton assemblage. Elevated pCO2 favored the smallest phytoplankton size class in terms of biomass, primarily picoeukaryotes, at the expense of chlorophyta and haptophyta in the nano-plankton size range. This shift in community composition and size structure was accompanied by a decline in the proportion of polyunsaturated FA (PUFA) to total FA content in the nano- and picophytoplankton size fractions. This decline was mirrored in a continuing reduction in the relative PUFA content of the dominant copepod, Calanus finmarchicus, which primarily fed on the nano-size class. Our results demonstrate that a shift in phytoplankton community composition and biochemical composition in response to rising CO2 can affect the transfer of essential compounds to higher trophic levels, which rely on their prey as a source for essential macromolecules.

Planktonic foraminiferal biostratigraphy and paleoenvironment of the Danian/Selandian in west-central Sinai (Egypt), implications from the Nukhul section

The foraminiferal analysis at the Danian/Selandian boundary of the Nukhul section (Egypt) enabled us to determine the biozones of Praemurica uncinata (P2); Morozovella angulata (P3a); Igorina albeari (P3b), and Acarinina soldadoensis/Globanomalina pseudomenardii (P4c). Thus, the base of Selandian is defined by the first occurrence of I. albeari and the P4c subzone covers unconformably the P3b subzone. The quantitative and qualitative analysis of the planktonic and benthic foraminifera assemblages and the isotopic analysis permitted characterization of the paleoclimate and paleoenvironment. Thus, at the middle to upper Danian, the environment was marine intertidal under a relatively cold climate. At the lower Selandian base of the Thanetian, a rise in the sea level was recorded and the warmer climatic conditions seem to be settling. In the upper Thanetian, we note the installation of colder weather conditions and a further sudden drop in sea level.

Diversity of Pico- to Mesoplankton along the 2000 km Salinity Gradient of the Baltic Sea.

Microbial plankton form the productive base of both marine and freshwater ecosystems and are key drivers of global biogeochemical cycles of carbon and nutrients. Plankton diversity is immense with representations from all major phyla within the three domains of life. So far, plankton monitoring has mainly been based on microscopic identification, which has limited sensitivity and reproducibility, not least because of the numerical majority of plankton being unidentifiable under the light microscope. High-throughput sequencing of taxonomic marker genes offers a means to identify taxa inaccessible by traditional methods; thus, recent studies have unveiled an extensive previously unknown diversity of plankton. Here, we conducted ultra-deep Illumina sequencing (average 105 sequences/sample) of rRNA gene amplicons of surface water eukaryotic and bacterial plankton communities sampled in summer along a 2000 km transect following the salinity gradient of the Baltic Sea. Community composition was strongly correlated with salinity for both bacterial and eukaryotic plankton assemblages, highlighting the importance of salinity for structuring the biodiversity within this ecosystem. In contrast, no clear trends in alpha-diversity for bacterial or eukaryotic communities could be detected along the transect. The distribution of major planktonic taxa followed expected patterns as observed in monitoring programs, but groups novel to the Baltic Sea were also identified, such as relatives to the coccolithophore Emiliana huxleyi detected in the northern Baltic Sea. This study provides the first ultra-deep sequencing-based survey on eukaryotic and bacterial plankton biogeography in the Baltic Sea.

Impact of ocean acidification on phytoplankton assemblage, growth, and DMS production following Fe-dust additions in the NE Pacific high-nutrient, low-chlorophyll waters

Abstract. Ocean acidification (OA) is likely to have an effect on the fertilizing potential of desert dust in high-nutrient, low-chlorophyll oceanic regions, either by modifying iron (Fe) speciation and bioavailability or by altering phytoplankton Fe requirements and acquisition. To address this issue, short incubations (4 days) of northeast subarctic Pacific waters enriched with either FeSO4 or dust and set at pH 8.0 (in situ) and 7.8 were conducted in August 2010. We assessed the impact of a decrease in pH on dissolved Fe concentration, phytoplankton biomass, taxonomy and productivity, and the production of dimethylsulfide (DMS) and its algal precursor dimethylsulfoniopropionate (DMSP). Chlorophyll a (chl a) remained unchanged in the controls and doubled in both the FeSO4-enriched and dust-enriched incubations, confirming the Fe-limited status of the plankton assemblage during the experiment. In the acidified treatments, a significant reduction (by 16–38 %) in the final concentration of chl a was measured compared to their nonacidified counterparts, and a 15 % reduction in particulate organic carbon (POC) concentration was measured in the dust-enriched acidified treatment compared to the dust-enriched nonacidified treatment. FeSO4 and dust additions had a fertilizing effect mainly on diatoms and cyanobacteria as estimated from algal pigment signatures. Lowering the pH affected mostly the haptophytes, but pelagophyte concentrations were also reduced in some acidified treatments. Acidification did not significantly alter DMSP and DMS concentrations. These results show that dust deposition events in a low-pH iron-limited northeast subarctic Pacific are likely to stimulate phytoplankton growth to a lesser extent than in today's ocean during the few days following fertilization and point to a low initial sensitivity of the DMSP and DMS dynamics to OA.

A calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the Sinemurian/Pliensbachian (early Jurassic, ~ 191 Ma) in Portugal

The Sinemurian/Pliensbachian boundary (~191Ma) is acknowledged as one of the most important steps in the radiation of planktonic organisms, especially primary producers such as dinoflagellates and coccolithophores. To date, there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary. The aim of this study is to characterize the palaeoenvironmental changes occurring across the Sinemurian/Pliensbachian boundary at the São Pedro de Moel section (Lusitanian Basin, Portugal) using micropalaeontology and organic geochemistry approaches. Combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea-level rise occurring above the boundary. The Lusitanian Basin was particularly restricted during the late Sinemurian with a relatively low sea level, a configuration that led to the recurrent development of black shales. After a sharp sea-level fall, the basin became progressively deeper and more open during the earliest Pliensbachian, subsequently to a major transgression. This sea-level increase seems to have been a global feature and could have been related to the opening of the Hispanic Corridor that connected the Tethys and palaeo-Pacific oceans. The palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of Tethyan waters by placolith-type coccoliths.

Geological map of the eastern sector of the Gorgoglione Basin (southern Italy)

In this paper we report new stratigraphic data related to a new geological map of the Miocene Gorgoglione Basin of southern Italy, traditionally considered as a piggy-back or wedge-top basin filled by a turbidite-like succession. Well exposed outcrops in the study area (eastern sector of the basin) show four unconformities in the Castelmezzano-Pietrapertosa area. Two of these unconformities pass to paraconformities southeastward, in the Cirigliano-Gorgoglione area. Based on new stratigraphic data the succession of the Gorgoglione Flysch can be divided into different informal units: Val Miletta formation and Gorgoglione supersynthem. The latter can be subdivided into the Cirigliano and Castelmezzano synthems. The previously established Cirigliano synthem is here divided into three subsynthems. The lowermost sediments of the Gorgoglione Flysch on the eastern sectors correspond to a complex unit (Val Miletta formation) including Numidian-like quartzarenites, Gorgoglionelike sandstones, and, at the top of the formation, an olistostrome of varicoloured clays, belonging to the Argille Variegate Group. The stratigraphic analyses and the biostratigraphic results based on calcareous plankton assemblage, improve the reconstruction of the geometries of the sedimentary bodies and the time-space facies evolution of the synthems. Sedimentologic and petrographic characters of the upper part of the Castelmezzano synthem show a clear fining and thinning upward trend. Medium- and fine-grained arenites, varying in composition from quartz sandstones to siltstones and shales, are locally marked by abundant planktonic foraminifera and are interpreted as contourites. Moreover, the relationships between tectonics and sedimentation are analyzed. The data are used to propose a scheme of the Burdigalian to Tortonian tectono-stratigrafiphic evolution of the eastern sector of the basin.

Toxicity of waters from the Rochester Embayment Area of Concern to the plankton species Pseudokirchneriella subcapitata and Ceriodaphnia dubia

The lower Genesee River and Rochester Embayment of Lake Ontario are a designated Area of Concern (AOC) under the binational Great Lakes Water Quality Agreement. The “degradation of phytoplankton and zooplankton populations” or plankton Beneficial Use Impairment (BUI) was classified as unknown and in need of further assessment in this AOC because water quality data suggested plankton communities could be effected and community data were either unavailable or indicated impacts. The plankton BUI may now be obsolete because local contaminant sources have been largely eliminated. The present study was conducted between July 2013 and August 2014 to assess the BUI-removal criteria: “AOC plankton bioassays confirm that toxicity in ambient waters (i.e., no growth inhibition) is not significantly higher than comparable non-AOC controls”. Acute and chronic toxicity of waters from 13 sites were quantified seasonally using standardized bioassays with the green alga Pseudokirchneriella subcapitata and water flea Ceriodaphnia dubia to test the hypothesis that toxicity of waters from AOC sites was not higher than that of waters from comparable non-AOC reference sites. Survival and reproduction of C. dubia did not differ significantly between site types, systems, or months. The growth of P. subcapitata did not differ between site types, but differed among systems and months. All results indicate that waters from AOC sites were no more toxic to both plankton species than waters from reference sites. Assuming test species represent natural plankton assemblages, water quality should not negatively affect survival and growth of resident plankton populations in the Rochester Embayment AOC.