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Coccolithophores are among the most important calcifying pelagic organisms. To assess how coccolithophore species with different coccolith-carbonate mass and distinct ecological resilience to ocean warming will influence the “rain ratio” and the “biological carbon pump”, 1 yr of species-specific coccolith-carbonate export fluxes were quantified using sediment traps moored at four sites between NW Africa and the Caribbean (i.e., CB-20°N/21°W, at 1214 m; M1-12°N/23°W, at 1150 m; M2-14°N/37°W, at 1235 m; M4-12°N/49°W, at 1130 m). Highest coccolith-CaCO3 fluxes at the westernmost site M4, where the nutricline is deepest along the tropical North Atlantic, were dominated by deep-dwelling small-sized coccolithspecies Florisphaera profunda and Gladiolithus flabellatus. Total coccolith-CaCO3 fluxesof 371 mg m−2 yr−1 at M4 were followed by 165 mg m−2 yr−1 at the north-easternmost CB, 130 mg m−2 yr−1 at M1, and 114 mg m−2 yr −1 at M2 in between. Coccoliths accounted for nearly half of the total carbonate flux at M4 (45%), much higher compared to 23% at M2 and 15% at M1 and CB. At site M4, highest ratios of coccolith-CaCO3 to particulate organic carbon fluxes and weak correlations between the carbonate of deep-dwelling species and particulate organic carbon suggest that increasing productivity in the lower photic zone in response to ocean warming might enhance the rain ratio and reduce the coccolith-ballasting efficiency. The resulting weakened biological carbon pump could, however, be counterbalanced by increasing frequency of Saharan dust outbreaks across the tropical Atlantic, providing mineral ballast as well as nutrients to fuel fast-blooming and ballast-efficient coccolithophore species.

Early detection of dense harmful algal blooms (HABs) is possible using ocean colour remote sensing. Some algorithms require a training dataset, usually constructed from satellite images with a priori knowledge of the existence of the bloom. This approach can be limited if there is a lack of in situ observations, coincident with satellite images. A laboratory experiment collected biological and bio-optical data from a culture of Karenia mikimotoi, a harmful phytoplankton dinoflagellate. These data showed characteristic signals in chlorophyll-specific absorption and backscattering coefficients. The bio-optical data from the culture and a bio-optical model were used to construct a training dataset for an existing statistical classifier. MERIS imagery over the European continental shelf were processed with the classifier using different training datasets. The differences in positive rates of detection of K. mikimotoi between using an algorithm trained with purely manually selected areas on satellite images and using laboratory data as training was overall in situ observations of non-harmful high chlorophyll blooms in the area would improve testing of the ability to distinguish harmful from non-harmful high chlorophyll blooms. This approach can be expanded to use additional wavelengths, different satellite sensors and different phytoplankton genera.

Monitoring temporal changes in phytoplankton dynamics in high latitude lakes is particularly timely for understanding the impacts of warming on aquatic ecosystems. In this study, we analyzed 33-years of high resolution (30 m) Landsat (LT) data for reconstructing seasonal patterns of chlorophyll a (chl a) concentration in four lakes across Finland, between 60°N and 64°N. Chl a models based on LT spectral bands were calibrated using 17-years (2000–2016) of field measurements collected across the four lakes. These models were then applied for estimating chl a using the entire LT-5 and 7 archives. Approximately 630 images, from 1984 to 2017, were analyzed for each lake. The chl a seasonal patterns were characterized using phenology metrics, and the time-series of LT-based chl a estimates were used for identifying temporal shifts in the seasonal patterns of chl a concentration. Our results showed an increase in the length of phytoplankton growth season in three of the lakes. The highest increase was observed in Lake Köyliönjärvi, where the length of growth season has increased by 28 days from the baseline period of 1984–1994 to 2007–2017. The increase in the length of season was mainly attributed to an earlier start of phytoplankton blooms. We further analyzed surface temperature (Ts) and precipitation data to verify if climatic factors could explain the shifts in the seasonal patterns of chl a. We found no direct relationship between Ts and chl a seasonal patterns. Similarly, the phenological metrics of Ts, in particular length of season, did not show significant temporal trends. On the other hand, we identify potential links between changes in precipitation patterns and the increase in the phytoplankton season length. We verified a significant increase in the rainfall contribution to the total precipitation during the autumn and winter, accompanied by a decline in snowfall volumes. This could indicate an increasing runoff volume during the beginning of spring, contributing to an earlier onset of the phytoplankton blooms, although further assessments are needed to analyze historical streamflow values and nearby land cover data. Likewise, additional studies are needed to better understand why chl a patterns in some lakes seem to be more resilient than in others. peerReviewed

Surface sediments were sampled at 18 stations from 7 to 64 m depth off the SE coast of Algarve to characterize the organic matter contents in the inner and middle shelf. For each sediment sample, grain size, mineralogy and total organic carbon analyses were carried out, as well as pigment analyses (19’ but-fucoxanthin, fucoxanthin, 19’ hex-fucoxanthin, chlorophyll-a, chlorophyll-b, pheophytin-a, pheophorbide-a, alpha-carotene, beta-carotene, anteraxanthin, diadinoxanthin, diatoxanthin, lutein and zeoxanthin). In addition, the ratios between each pigment and the total organic carbon (TOC) percentage, and between the chlorophyll-a concentration and the pheophytin-a and the pheophorbide-a concentrations were calculated to establish pigment indices. A Multidimensional scaling (MDS) analysis highlights three regions in the SE coast of Algarve according to depth, percentages of TOC, sediment grain size and mineralogy, concentration of pigments highly susceptible to degradation, concentration of refractory pigments (pigments not susceptible to degradation) and different preservation conditions (based on the pigment index values). The results highlight a correlation between pigments concentration and environmental variables, showing the eastern limit of West coastal upwelling plumes influence along the Algarve continental shelf.

Phytoplankton size structure is an important indicator of the state of the pelagic ecosystem. Stimulated by the paucity of in situ observations on size structure, and by the sampling advantages of autonomous remote platforms, new efforts are being made to infer the size-structure of the phytoplankton from oceanographic variables that may be measured at high temporal and spatial resolution, such as total chlorophyll concentration. Large-scale analysis of in situ data has revealed coherent relationships between size-fractionated chlorophyll and total chlorophyll that can be quantified using the three-component model of Brewin et al. (2010). However, there are variations surrounding these general relationships. In this paper, we first revise the three-component model using a global dataset of surface phytoplankton pigment measurements. Then, using estimates of the average irradiance in the mixed-layer, we investigate the influence of ambient light on the parameters of the three-component model. We observe significant relationships between model parameters and the average irradiance in the mixed-layer, consistent with ecological knowledge. These relationships are incorporated explicitly into the three-component model to illustrate variations in the relationship between size-structure and total chlorophyll, ensuing from variations in light availability. The new model may be used as a tool to investigate modifications in size-structure in the context of a changing climate.

Dietary inclusion of IMTA-cultivated Gracilaria vermiculophylla was evaluated in rainbow trout. Growth and feed efficiency were determined in fish fed 0 % (CTRL), 5 % (G5), and 10 % (G10) of the red seaweed for 91 days. Carotenoid concentration (skin and muscle), immunological parameters, and intestinal morphology were also evaluated. G10 group showed the lowest final body weight, with feed and protein efficiency ratios being significantly lower than the CTRL. Although protein intake was similar among groups, G10 diet induced the lowest protein retention and gain probably due to its smallest intestine diameter and lowest villi height. Fish fed G10 diet displayed higher carotenoid content in the skin (16.7 μg g−1) when compared with the CTRL group, but a lower concentration was registered in the flesh (0.23 μg g−1). Instrumental color showed that fillets were more luminous (L*), less yellowish (b*), and more reddish (a*) with seaweed inclusion and the lowest chrome intensity (C*) in the G10 group confirmed the lowest muscle carotenoid content in these fish. G5 diet enhanced the innate immune response of rainbow trout inducing the highest peroxidase, alternative complement (ACH50), and lysozyme activities. The inclusion of Gracilaria meal in diets for rainbow trout is possible up to 5 %, but a higher inclusion level impairs growth.

The spatio-temporal variation of microphytobenthos (MPB) at the scale of a large estuary (Tagus estuary, Portugal) was studied using a combination of field and satellite remote sensing data during 2003. This is the first attempt to use remote sensing to study MPB in an ecosystem with a Mediterranean-like climate. Satellite pour l'Observation de la Terre (SPOT) and Medium Resolution Imaging Spectrometer (MERIS) images were used to map benthic microalgae through the application of a Normalized Difference Vegetation index (NDVI). A significant relationship between in-situ benthic chlorophyll a measurements and SPOT NDVI values was used to derive a map for biomass spatial distribution. At the scale of the whole intertidal area, NDVI time-series from 2003 revealed that MPB showed clear temporal variations, with lower values observed in summer compared to winter. This seasonal trend was found both in the SPOT and MERIS images and may be the result of extreme high temperatures that inhibit MPB growth. The main MPB biofilms were spatially stable through time at a large scale. Maximum NDVI values during the winter were found in the high shore with decreasing NDVI values towards the low shore. MPB light limitation at the lowest bathymetries is likely to occur in winter due to the high turbidity of Tagus estuary. The biomass spatial distribution map, obtained for January 2003, indicated low values ranging from 0 to 20 mg Chl a m

During summer 2008 and spring 2009, surface oceanographic surveys were carried out around three islands of the Azores archipelago (Terceira, Sao Miguel and Santa Maria) to assess the phytoplankton distribution and associated physico-chemical processes. The Azores archipelago is a major feature in the biogeochemical North Atlantic Subtropical Gyre (NAST) province although its influence on the productivity of the surrounding ocean is poorly known. Surface phytoplankton was studied by microscopy and HPLC (High Precision Liquid Chromatography). The mean values for biomass proxy Chlorophyll a (Chl a ) ranged from 0.04 to 0.55 μg L −1 (Chl a maximum = 0.86 μg L −1 ) and coccolithophores were the most abundant group, followed by small flagellates, Cyanobacteria, diatoms and dinoflagellates being the least abundant group. The distribution of phytoplankton and coccolithophore species in particular presented seasonal differences and was consistent with the nearshore influence of warm subtropical waters from the south Azores current and colder subpolar waters from the north. The satellite-derived circulation patterns showed southward cold water intrusions off Terceira and northward warm water intrusions off Santa Maria. The warmer waters signal was confirmed by the subtropical coccolithophore assemblage, being Discosphaera tubifera a constant presence under these conditions. The regions of enhanced biomass, either resulting from northern cooler waters or from island induced processes, were characterized by the presence of Emiliania huxleyi . Diatoms and dinoflagellates indicated coastal and regional processes of nutrient enrichment and areas of physical stability, respectively.

The main goal of this study was to evaluate short-term interactions between increased CO2, UVR and inorganic macronutrients (N, P and Si) on summer phytoplankton assemblages in the Ria Formosa coastal lagoon (SW Iberia), subjected to intense anthropogenic pressures and highly vulnerable to climate change. A multifactorial experiment using 20 different nutrient-enriched microcosms exposed to different spectral and CO2 conditions was designed. Before and after a 24-h in situ incubation, phytoplankton abundance and composition were analysed. Impacts and interactive effects of high CO2, UVR and nutrients varied among different functional groups. Increased UVR had negative effects on diatoms and cyanobacteria and positive effects on cryptophytes, whereas increased CO2 inhibited cyanobacteria but increased cryptophyte growth. A positive synergistic interaction between CO2 and UVR was observed for diatoms; high CO2 counteracted the negative effects of UVR under ambient nutrient concentrations. Nutrient enrichments suppressed the negative effects of high CO2 and UVR on cyanobacteria and diatoms, respectively. Beneficial effects of CO2 were observed for diatoms and cryptophytes under combined additions of nitrate and ammonium, suggesting that growth may be limited by DIC availability when the primary limitation by nitrogen is alleviated. Beneficial effects of high CO2 and UVR in diatoms were also induced or intensified by ammonium additions. info:eu-repo/semantics/publishedVersion

Domoic acid (DA) is a neurotoxin produced by Pseudo-nitzschia diatoms that is accumulated in the highest concentrations in filter-feeding organisms, such as bivalve molluscs. Although DA is a water-soluble molecule that is rapidly cleared from most marine organisms, it appears that octopus may consistently contain DA in the digestive gland. To test this hypothesis, specimens of Octopus vulgaris were caught for DA analysis when Pseudo-nitzschia cells were not observed in seawater and DA was not detected in octopus food items, i.e. mussels. DA was consistently detected in each octopus specimen (n=32) analysed and its concentrations varied from 1.0 to 26.6 µg g−1. DA sub-cellular distribution was evaluated in the digestive gland of six specimens in order to prove whether DA preferably accumulates in some cell compartment. DA was predominantly found (>90%) in the soluble fraction (cytosol) and to a lesser extent in the insoluble fractions (nucleic, mitochondrial, lysosomal, microsomal). This disposit...

The microphytobenthos (MPB) – Hydrobia ulvae trophic interaction is one of the main channels of material transfer to higher trophic levels in intertidal mudflats. A new non-invasive approach to evaluate the grazing activity of H. ulvae on microphytobenthos is proposed. The effects of season and period (combination of tide and day/night) on ingestion rates of H. ulvae (using 14Clabeled MPB) and egested pheopigments a (using HPLC pigment analysis) were also investigated. H. ulvae ingestion rate was found to vary significantly over season and period, being higher in summer and during diurnal low tide periods. This is possibly related to higher growth rates of H. ulvaein summer, as well as to an increase in surface MPB biomass during diurnal low tides. A highly significant relationship was found between ingested chl a and egested pheophorbide a, allowing the estimation of ingestion rate from the amount of egested pheophorbide a on H. ulvae faecal pellets. This new non-invasive methodology may allow the improvement of long-term studies of consumption rates and the evaluation of grazing of H. ulvae on MPB. We thank I. Macário, P. Pochelon and T. Salvaterra for assistance in field work; M. Ruivo for assistance in HPLC and A. Luísa Santos for assistance in the Radioisotope Laboratory; A. Almeida for hosting the radioisotope work in the Radioisotope Laboratory at the Department of Biology, University of Aveiro; and 3 anonymous reviewers for critical comments on the manuscript. H.C. was supported by FCT – Fundação para a Ciência e Tecnologia (SFRH/BD/23720/ 2005). This work is part of the research project Benthic link – trophic links regulated by tidal and daily rhythms: benthic microflora and fauna in estuaries’, funded by FCT (POCI/BIABDE/61977/2004). Both grants were allocated by FCT under the Support Community Framework III, Operational Programme Science, Technology and Innovation. The methods used in this study comply with Portuguese legislation on animal experimentation. published

The distribution and composition of phytoplankton assemblages were studied in the Nazare submarine canyon, during an upwelling event, using high-performance liquid chromatography (HPLC) pigment analysis, complemented by microscopic qualitative observations. High chlorophyll a (Chl a) concentrations were recorded in the canyon head, near the coast, where values greater than 4 μg L− 1 were observed. In contrast, Chl a was relatively low in offshore regions, with values below 0.5 μg L− 1. The most abundant accessory pigments were fucoxanthin, peridinin, diadinoxanthin and 19′-hexanoyloxyfucoxanthin. Pigment data information was analyzed using the CHEMTAX software to estimate the contribution of different taxonomic groups to total Chl a. North of the canyon head, an area with high concentration of peridinin-containing dinoflagellates was identified (with presence of chain-forming toxic dinoflagellates). The presence of these organisms was associated with mixed water columns and phosphate values lower than the ones south of the canyon head, where a dominance of diatoms was recorded. The rest of the study region showed a dominance of prymnesiophytes and a significant contribution of cyanobacteria at oceanic stations. This study demonstrates the usefulness of using pigment analysis to study spatial distribution of phytoplankton groups in relation to a complex physical environment.

International audience; Intertidal soft sediment microphytobenthic biofilms are often dominated by diatoms, which are able to regulate their photosynthesis by physiological processes (e.g. down-regulation through the xanthophyll cycle, referred to as non-photochemical quenching, NPQ) and behavioural processes (e.g. vertical cell movement in the sediment–biofilm matrix). This study investigated these 2 processes over a 6 h emersion period using chemical inhibitors under 2 light treatments (ambient and constant light at 300 µmol m–2 s–1). Latrunculin A (Lat A) was used to inhibit cell movement and dithiothreitol (DTT) to inhibit NPQ. HPLC analysis for chlorophyll a and spectral analysis (Normalised Difference Vegetation Index) indicated that Lat A significantly inhibited cell movement. Photosynthetic activity was measured using variable chlorophyll fluorescence and radiolabelled carbon uptake and showed that the non-migratory, Lat A-treated biofilms were severely inhibited as a result of the high accumulated light dose (significantly reduced maximum relative electron transport rate, rETRmax, and light utilisation coefficient, α, compared to the migratory DTT and control-treated biofilms). No significant patterns were observed for 14C data, although a decrease in uptake rate was observed over the measurement period. NPQ was investigated using HPLC analysis of xanthophyll pigments (diatoxanthin and the percentage de-epoxidation of diadinoxanthin), chlorophyll fluorescence (change in maximum fluorescence yield) and the 2nd order spectral derivative index (diatoxanthin index). Patterns between methods varied, but overall data indicated greater NPQ induction in the non-migratory Lat A treatment and little or no NPQ induction in the DTT and control treatments. Overall, the data resulted in 2 main conclusions: (1) the primary response to accumulated light dose was vertical movement, which when inhibited resulted in severe down-regulation/photoinhibition; (2) diatoms down-regulated their photosynthetic activity in response to accumulated light dose (e.g. over an emersion period) using a combination of vertical migration and physiological mechanisms that may contribute to diel and/or tidal patterns in productivity.

Tagus intertidal microphytobenthos (MPB) assemblages were characterized over a wide range of sediment type and tidal height and the possible effects of these variables on MPB spatial distribution and photo-adaptation mechanisms were investigated. Two transects with six different sediment type and different tidal height sites were sampled once every two months from 2002 to 2004. Upper shore and sandy sites showed higher chlorophyll a (chl a) content, with sandy sediments showing a biomass peak in late winter–early spring, and muddy sites showing no obvious seasonal pattern. Stepwise multiple linear regressions showed that only SiO2, tidal height and sediment particle size 60 μm. Epipelic biofilms showed evidence of being low light-acclimated (high fucoxanthin/chl a) and of photo-regulating by vertical migration movements (presence of endogenous vertical rhythms and lower diatoxanthin/diadinoxanthin). Epipsammic biofilms showed higher diatoxanthin/diadinoxanthin ratios and no vertical migration rhythms. Thus, the two diatom biofilm types had distinct strategies to photo-regulate: epipelic diatoms using vertical migration to position themselves at the sediment depth of optimum light conditions, and epipsammic diatoms using the xanthophyll cycle to photo-regulate. Further studies comparing epipsammic and epipelic assemblages are necessary to better understand MPB photo-regulation mechanisms.

The phytoplankton distribution and composition in Lisbon bay was studied, at a short time scale based on a weekly sampling, during one year (April 2004 – May 2005), using microscopic examination and pigment analysis with high-performance liquid chromatography (HPLC). This work is a contribution to the knowledge on species succession and ecology of coastal communities. The frequency of the sampling permitted monitoring peak blooming and decaying, a process which frequently occurred within 1 –2 weeks. Cell counts determined that the classes Dinophyceae, Bacillariophyceae and Prymnesiophyceae dominated the assemblages. Maxima abundances and diversity of phytoplankton were observed from spring to autumn. HPLC analysis reflected the major seasonal variations observed by the cell counts and in addition detected the presence of four small sized phytoplankton classes that were not identified by microscopy. Phytoplankton counts were essential to identify the main contributing species to total chlorophyll a. Fucoxantin, peridinin and 19′-hexanoyloxyfucoxanthin appeared as good indicators for diatoms, dinoflagellates and coccolithophores, respectively, with synchronized seasonal variations and significant positive correlations.

The effects of the motility inhibitors 2,3-butanedione monoxime (BDM) and latranculin A (Lat A) on the motility, photosynthetic activity and pigment composition of the benthic diatoms Cylindrotheca closterium and Pleurosigma angulatum were studied. BDM inhibited diatom gliding, preventing motility at concentrations of 12.5 mM and 50 mM for C. closterium and P. angulatum, respectively. For both species, the quantum yield of PSII (ΔF/Fm′) decreased with increasing concentrations of BDM. Reduced excitation at PSII reaction centres were caused by BDM-induced conversion of the pigment diadinoxanthin to diatoxanthin, through the activation of the xanthophyll cycle. Lat A inhibited diatom gliding, preventing motility at concentrations of 0.1 μM and 0.25 μM for C. closterium and P. angulatum, respectively. Concentrations of Lat A as high as 1 μM showed no significant effects on the PSII quantum yield, on the light-response curves of relative electron transport rate (initial slope of light curve, a, and maximum re...

Increasing levels of a mixture of Ulva spp. (Ulva rigida and Ulva lactuca) produced in an integrated multi-trophic aquaculture (IMTA) system were evaluated in Nile tilapia. A control diet (CTRL) was compared with two experimental isonitrogenous (36 %) and isoenergetic (20 kJ g−1) diets containing 5 % (U5) and 10 % (U10) of Ulva spp. meal. Duplicate groups of 18 fish (255 g initial body weight) were reared at 25 °C and fed each diet for 68 days to evaluate carotenoid deposition, flesh organoleptic properties and immunological response. By the end of the trial, all groups of fish showed similar final body weight and specific growth rate. Whole body composition was also similar among treatments. The dietary incorporation of Ulva spp. meal increased total carotenoid content in the skin, with fish fed U5 displaying significantly higher levels (6.5 μg g−1) than the CRTL (1.4 μg g−1). No carotenoids could be found in tilapia muscle. Muscle colour determined using a spectrocolorimeter indicated that tilapia fillets from fish fed U10 showed the highest lightness (highest L* value) and yellowness (less negative b* value), but the lowest redness (lowest a* value). Furthermore, sensory attributes of flesh showed no significant effects of dietary treatments on visual, olfactory, texture and flavour parameters, with the exception of sour parameter that was lowest in U10-fed tilapia. The dietary inclusion of Ulva spp. meal had no beneficial effect on lysozyme or peroxidase activity, but the complement activity (ACH50), an important component of innate immune system in fish, increased concomitantly with the dietary inclusion level of Ulva spp. meal. The inclusion of Ulva spp. meal in diets for Nile tilapia seems to be possible up to 10 % without major effects on growth performance or flesh organoleptic properties but enhancing the innate immune response of the fish. © 2015, Springer Science+Business Media Dordrecht. The authors acknowledge M. Pereira and Carolina Beltrán for their valuable help during sampling of fish and laboratorial work. This work was funded by FEDER (European fund for regional development), in the context of the Operational Competitiveness Programme – COMPETE, by FCT—Fundação para a Ciência e a Tecnologia, under the project Project Benefits (PTDC/MAR/105229/2008) n. FCOMP-01-0124-FEDER-010622.

A 7-year (March 1999eNovember 2005) monitoring program was developed in the Tagus estuary to study phytoplankton dynamics and several key controlling factors, namely nutrient content, light availability, atmospheric and hydrodynamic conditions (temperature, wind, rainfall, river flow, and salinity). Water was collected at four sampling sites on a monthly basis. Phytoplankton biomass, analyzed as Chl a, was moderate to low, when compared to other mesotidal estuaries: interannual average Chl a values ranged from 1.4 in winter to 8.0 mg L � 1 in summer. A consistent seasonal pattern was observed, with a unimodal peak extending from late spring to summer. The phytoplankton community, as determined by biomarker pigment concentration using HPLC and CHEMTAX, was dominated by diatoms (57%), and included cryptophytes (23%), dinoflagellates (6.8%), chlorophytes (5.4%), euglenophytes (4.9%), and prasinophytes (2.6%). The method was capable of detecting phytoplankton taxa generally underestimated or overlooked when using standard microscopic techniques. Diatoms were the main bloom-formers in the summer Chl a maximum. A stepwise regression analysis showed that air temperature, river flow and irradiance explained 47% of the observed Chl a variance, illustrating the importance of climatic factors as driving forces for seasonal and interannual variability of phytoplankton.

The effectiveness of two HPLC methods (a monomeric C18 column with a high ion strength solvent gradient and a monomeric C8 column with a pyridine-containing mobile phase) in the separation, identification, and quantification of pigments are compared, using phytoplankton, microphytobenthos, and algal cultures. Although the two studied methods showed good analytical resolution, the C18 method presents a higher discrimination for several carotenoid pigments. On the other hand, the C8 method allows the separation of chlorophylls c1, c2, and Mg-2, 4-divinyl phaeoporphyrin a5 monomethyl ester as well as the pair chlorophyll a/divinyl Chl a. The C18 method had a shorter elution program and a lower solvent flow rate, making it cheaper and faster than the C8 method. Furthermore, the C18 method showed significantly lower detection and quantification limits, a particularly important advantage for pigments present in trace amounts in both phytoplankton and microphytobenthic samples. Differences in the sensitivity of the two studied methods were due mainly to differences in flow rate, with significantly higher peak areas for slower flow rates. No method is ideal for all pigments and sample types and the choice of method should be made in accordance with the objective of each study, taking into consideration the advantages and disadvantages identified for each method.

The role of hydrological droughts in shaping meiofauna abundance through alterations in biofilm biomass and composition was investigated. In January 2005, continental Portugal was under a moderate to severe drought resulting from a 40% to 60% decrease in rainfall during the previous 12 months relative to the long-term average (1961–1990). Reservoir capacity was reduced by 30–50% relative to average values and the width of streams was reduced by 20–80% in the Zezere River Basin (central Portugal). Algal biomass and algal class composition of biofilms was assessed through quantification of algal pigments in three reservoir and six river locations. During drought, habitat alterations are expected to be sharp in rivers while, in the absence of water quality deterioration, the habitat characteristics of reservoirs are expected to remain fairly unaffected. Chlorophylls and carotenoid pigments were extracted from biofilm samples and analysed using high performance liquid chromatography (HPLC). In the winter of 2003, during the period of average rainfall, biofilm biomass did not exceed 5 μg chlorophyll a cm−2 at any location. River biofilm biomass was roughly half of that measured in the reservoirs. In the winter of 2005 (drought), biofilm biomass increased by more than 5-fold in river locations and remained low or decreased in the reservoirs. Algal biofilms were either dominated by Bacillariophyceae or by Chlorophyceae regardless of the existence of drought. The relative contribution of Bacillariophyceae to total biofilm biomass was higher during the drought than under average hydrological conditions. The abundance of harpacticoids, cladocerans and ostracods was favoured by the drought only in the reservoirs where an increase in diatom proportion in biofilms was observed. The increase in the abundance of cyclopoid copepods, turbellarians, nematodes and chironomids in rivers during the drought could be explained by algal class composition and biomass of biofilms and environmental variables (organic matter sediment content, phosphorus availability content and sediment granulometry). The hydrological drought appears to regulate meiofauna abundance only in river locations, possibly through the promotion of the growth of biofilms and the availability of organic matter deposited in rivers during the drought.

Samples of microphytobenthos from the Tagus estuary were analysed for photosynthetic pigments by spectrophotometry and High Performance Liquid Chromatography (HPLC). Chlorophyll a values obtained with HPLC and spectrophotometry methods presented a highly significant positive correlation for both spectrophotometric methods used (with and without the correction for pheopigments), but this relationship depended on the type of sediment. We concluded that spectrophotometric methods give reliable Chl-a values, being suited for routine analysis, when a vast number of replicates is needed. However, for the correct estimation of pheopigments, HPLC analysis is indispensable. In the literature, Chl-a estimations are expressed per content (μg g−1) or concentration (mg m−2). We discuss the influence of sediment type on the results depending on the type of unit used, and propose a simple conversion factor based on sediment water content.

Intertidal flats are frequently colonised by microphytobenthos (MPB) assemblages that form transient biofilms at the sediment surface which are responsible for large fractions of estuarine primary production. The large spatio-temporal variability in MPB biomass distribution in concert with the fact that tidal flats can cover many km2 makes the use of remote sensing particularly useful in assessing MPB distribution. Water content, sediment type and MPB vertical migration are variables that affect the relationship between ground truth measurements and remote sensing of benthic chlorophyll. The effect of chlorophyll depth distribution (top 2 mm) on the relationship between benthic chlorophyll and several remote sensing indices (NDVI, PI, R562/R647, derivative indices and PAM fluorescence) was investigated over a 2 year sampling period at 6 sites (Tagus estuary, Portugal). Additionally, the effect of the dark adaptation time required to measure the minimum fluorescence parameter (F0) was also tested. Sediment type strongly affected MPB depth distribution with muddy sites showing a strong negative exponential decay in chlorophyll with distance from the surface while sandy sites had a homogenous distribution over the same scale (2 mm). Chlorophyll content (mass per unit mass, μg g− 1) in the top 2 mm was better correlated with remote sensing indices than concentration (mass per unit volume, mg m− 3), both for NDVI (0.72 vs. 0.45) and for PAM fluorescence (0.70 vs. 0.55). Separating the data by transect increased the correlation values in all situations. A fitted model of chlorophyll depth distribution showed that the effect of asymmetrical chlorophyll depth distribution was stronger on the correlations between chlorophyll concentration and NDVI than on chlorophyll content and NDVI (0.46–2 mm vs. 0.74–125 μm, muddy site) the same was valid for fluorescence (0.66–2 mm vs. 0.92–125 μm, muddy site). Dark adapting the samples for more than 5 min did not result in any significant difference in the relationship between F0 and chlorophyll a. The residuals from the regression of chlorophyll content on NDVI were positively correlated (0.7) with the mass per unit of mass of sediment

The abundance and distribution of microphytobenthic pigments determined by HPLC (chlorophylls and carotenoids) were compared between muddy and sandy sediments of the Tagus estuary (Portugal). In the two types of sediment, with similar periods of illuminated emersion, chlorophyll a concentrations on a per area basis (mg m(-2)) were comparable (down to 2 mm). Pigment analysis also revealed similar microphytobenthic communities in terms of algal classes. Diatoms were the dominant microalgae, but cyanophytes, euglenophytes and phanerogam debris were also present. For both muddy and sandy sediments, microphytobenthic biomass showed a high level of variability both within and between two consecutive years. Microphytobenthos was highly stratified in the mud, with most of the chlorophyll a occurring in the top 500 pm. In the sand, relatively constant concentrations were found throughout the sediment profile down to 3 rum. This is probably related to deeper light penetration in sandy sediment and/or increased physical mixing caused by invertebrate activity or overlying currents, leading to the burial of an important fraction of the microphytobenthic cells. Differences observed in the intensity of sediment coloration of muddy and sandy sediments might have resulted from the different vertical distribution of benthic biomass. (c) 2005 Elsevier Ltd. All riahts reserved.

The induction of non-photochemical quenching of chlorophyll fluorescence (NPQ) and its relationship with the operation of the xanthophyll cycle were studied in estuarine microphytobenthos assemblages. NPQ and xanthophyll cycle operation were characterised by quantifying the induction kinetics and light-response curves of NPQ formation and of the production of xanthophyll cyle pigments diadinoxanthin (DD) and diatoxanthin (DT), on suspensions of benthic microalgae collected during two spring-neap tidal cycles, in summer (July) and in winter (November). The NPQ light response was characterised by a large intraday variability and by the high NPQ values attained under high irradiances. Maximum daily NPQ often reached values above 4.0, and values above 5.0 were observed on 2 days during the November sampling period. Changes in NPQ were generally followed by proportional variations in the DT content, both during exposure to high light and upon transition from darkness to low light, leading to highly significant correlations between NPQ and the DT content or the degree of de-epoxidation, DT / (DD + DT). Higher NPQ values in the dark than under low light were consistently observed. This was due to the generalised increase of Fm′ levels under low light to values higher than the Fm measured in the dark, and was associated to the decrease of the DT content upon exposure to low light. Significant seasonal variability was found regarding the parameters related to NPQ induction kinetics, indicating a higher capacity for NPQ operation in November than in July, both in the dark and as a response to high light. This seasonal variation in the NPQ light response was found to be associated to substantial changes in the taxonomic composition of microphytobenthos assemblages, and was interpreted as resulting from changes in the potential photoprotective response associated to thermal acclimation to winter conditions.

The spatial and temporal variability of phytoplankton abundance (in terms of chlorophyll a and cell number), inorganic nitrogen, suspended particulate matter (SPM), and light availability was determined throughout one year in the Tagus estuary, Portugal. Chlorophyll a concentrations showed a strong seasonal variation with values ranging from 1 to 32 μg l−1(average 5.4 μg l−1). Chlorophyll patterns were unimodal for sites 1, 2, and 3 and bimodal for site 4. Diatoms and cryptophytes were, throughout the year, the dominant groups in this shallow and unstratified estuarine system. Nitrate concentrations were seasonally related to river flow and ammonium concentrations spatially related to sources of sewage input. Lower river inputs and long water residence times during summer initially promoted the accumulation of phytoplankton, but the resulting low dissolved inorganic nitrogen (DIN) concentrations lead to limitation of phytoplankton growth. Chlorophyll a and DIN values obtained in the present study were comparable to those reported 20 years ago for the Tagus estuary.

Pulse modulated fluorescence has increasingly been used as an ecological tool to examine changes in the vertical distribution of microphytobenthic cells within the upper layers of estuarine sediments (most often using the minimum fluorescence yield F(o)) as well as to indicate the health of the community (using the maximum PS II quantum efficiency F(v)/F(m)). However, the practicalities of in situ measurements, often dictates that short dark adaptation periods must be used ( approximately 15 min). The use of far-red light as an alternative to dark adaptation was investigated in natural migratory microphytobenthic biofilms and artificial non-migratory biofilms. Prolonged periods of darkness ( approximately 24 h) were not adequate to achieve 'true' measurements of F(o) and F(v)/F(m), which require complete oxidation of Q(A) and full reversal of non-photochemical quenching (NPQ). In some instances, stable values were only achieved using far-red light. Prolonged exposure to dark/far-red light led to a downwards migration of cells in natural assemblages, as seen by a reduction in both F(o) and the maximum fluorescence yield (F(m)). In non-migratory biofilms, F(m) increased in the dark and far-red treatments, indicating a reversal of NPQ, whereas F(o) decreased in far-red light but increased in the dark. It is suggested that far-red light and darkness differentially affected the balance between NPQ reversal and Q(A) oxidation that lead to the measured F(o) yield. The use of far-red light as an alternative to dark adaptation is discussed and the implications of short (e.g., 15 min) dark adaptation times used in situ are discussed with reference to the vertical migration of cells within sediment biofilms.

Pigment degradation by Hydrobia ulvae, feeding on an intertidal mudflat dominated by diatoms, was studied in the laboratory. HPLC analysis identified significantly higher amounts of pheopigments in grazed sediment and a decrease in the concentrations of major chlorophylls (a and c1+c2) and carotenoides (fucoxanthin, diadinoxanthin, and β-carotene). Grazing by H. ulvae leads to a stronger pheophorbide a accumulation relative to pheophytin a. Dominant chlorophyll a degradation products were the less polar pheophorbide a4 and pheophytin a2. These pigments were identified in very high concentrations in H. ulvae faecal pellets. Although a major disadvantage of the HPLC method is the uncertainty regarding the extent and rate of pigment conversion into colourless products, these data strongly suggest the possible use of pheophorbide a4 and pheophytin a2 as useful markers for intertidal microphytobenthos grazing by H. ulvae.

The first crucial step in the chromatographic analysis of pigments by HPLC is the extraction of a sample. In this study, the extraction efficiencies of major pigments from a benthic microalgae community of an intertidal sediment by acetone and methanol are compared. The influence of extraction time and the use of sonication on pigment recovery is also examined. Extraction with acetone underestimated chlorophyll-c 2 and pheophorbide-a, while methanol extraction underestimated pheophythins-a and β-carotene. In methanol, long extraction times (6-24 h) generally yielded lower pigment concentrations, possibly due to isomerization and/or pigment degradation. Acetone is a better option if long extraction times are used. For extraction times of 15 min, higher pigment concentrations were usually found in sonicated extracts. No significant effect of sonication was observed for longer extraction times (2, 6 and 24 h). There is no ideal method for pigment extraction and results are probably highly dependent on several factors such as the sediment type, the microphytobenthic community present, the solvent gradient and the HPLC column. Nevertheless, in view of the strong underestimation of chlorophyll-c 2 in acetone extracts, we recommend the use of 15 min extraction in methanol after 30s of sonication for HPLC sedimentary pigment analysis.

The use of HPLC pigment analysis has become a widespread tool for investigating the taxonomic composition of phytoplankton. However, for micropytobenthos, due to the complexity of these communities and the accumulation of vegetal senescent material, the application of this technique presents further problems. Samples of unialgal cultures from representative taxa of microphytobenthos and samples of surface sediment from intertidal mudflats were collected, extracted in methanol and analyzed for photosynthetic pigments in a HPLC system, with a fluorimeter and a photodiode array detector. A total of 11 chlorophylline pigments and 19 carotenoids were identified. Absorbance chromatograms from cultures and natural populations are displayed. Pigment ratios from five species belonging to different taxonomic classes are compared. Pigment composition and diversity of intertidal muddy sites are discussed; the increase of degraded compounds of chlorophyll a and carotenoids along a vertical profile of 5 cm is shown on different sediment types.

The main aim of this study was to evaluate the temporal changes in the phytoplankton community of the Tagus Estuary and to identify the stressors involved. Environmental and phytoplankton data were gathered from several studies conducted in the 1960s, 1980s and from 1999 to 2010 (2000s). Phytoplankton data included information on the community composition through microscopy. No significant change was found between temperature and nitrogen values in the three periods. Chlorophyll a concentrations varied throughout the years, and the lowest concentrations were observed after 2004. Significant differences were also found between phytoplankton cell abundances, lower in the 1980s compared to the ones recorded in the 2000s. In the 1980s, diatoms were the most abundant group in the majority of samples and were found to be associated with nitrogen concentrations (canonical correspondence analysis), which was not observed in the 2000s. In the period 2006–2007, the importance of diatoms decreased and smaller cells became more abundant (e.g. cryptophytes, euglenophytes, prasinophytes). The ratio cryptophyta/bacillariophyta seems to yield an increase from 1 in 2006–2007. Mesodinium rubrum and Dinophysis produce recurrent toxic blooms in the adjacent coastal area. We can speculate that the estuary can be a cryptophyte producer to sustain the cryptophytes-M. rubrum-Dinophysis trophic relationship. A top-down hypothesis (shellfish grazing) is considered to explain the change in the phytoplankton community. A quantitative tool, the Phytoplankton Community Index (PCI), yielded a significant deviation of the community, from the 1980s to the 2000s, suggesting a shift toward the dominance of small cells.

The Firth of Lorn is at the mouth of one of Scotland's largest fjordic sea lochs, Loch Linnhe. This sea loch, which is fed by a number of other inner lochs, supplies a significant flow of freshwater, which frequently causes the stratification of the water column. To investigate how environmental conditions influence the spatial distribution of phytoplankton in this region water samples were collected for phytoplankton (pigments and microscopy), and other environmental variables including nutrients. Chemotaxonomy was used to estimate the contribution of different taxonomic groups to total chlorophyll a (phytoplankton biomass index). Good agreement was obtained between chemotaxonomy and microscopy data. The highest levels of chlorophyll a (∼2.6 mg m −3 ) were found in the vicinity of Oban Bay, where cryptophytes, the most abundant group, dinoflagellates and other flagellates thrived in the stratified water column. Centric diatoms, mainly Chaetoceros sp. and Skeletonema costatum , were associated with NH 4 and SiO 2 concentrations and stratification, while pennate diatoms, mainly Cylindrotheca sp. and Nitzchia sp., were found to be associated with NO 3 + NO 2 and high surface mixed layer depths. Four diatom groups were identified in accordance to their surface to volume ratios, as well as their affinity to environmental parameters (nutrients) and turbulence. This study used a combination of physico-chemical data, classical microscopy methods (appropriate for large cells > 20 μm) and HPLC-CHEMTAX approaches (for large and small cells) to evaluate the distribution of phytoplankton functional groups in a fjordic coastal area.

Chlorophyll a concentration (Chl) product validation off theWestern Iberian coast is here undertaken by directly comparing remote sensing data with in situ surface reference values. Both standard and recently developed alternative algorithms are considered for match-up data analysis. The investigated standard products are those produced by the MERIS (algal 1 and algal 2) and MODIS (OC3M) algorithms. The alternative data products include those generatedwithin the CoastColour Project and Ocean Color Climate Change Initiative (OC-CCI) funded by ESA, as well as a neural net model trained with field measurements collected in the Atlantic off Portugal (MLPATLP). Statistical analyses showed that satellite Chl estimates tend to be larger than in situ reference values. The study also revealed that a non-uniform Chl distribution in the water column can be a concurring factor to the documented overestimation tendency when considering larger optical depth match-up stations. Among standard remote sensing products, MODIS OC3M and MERIS algal 2 yield the best agreement with in situ data. The performance of MLPATLP highlights the capability of regional solutions to further improve Chl retrieval by accounting for environmental specificities. Results also demonstrate the relevance of oceanographic regions such as the Nazaré area to evaluate how complex hydrodynamic conditions can influence the quality of Chl products. This studywas performed in the framework of HabSpot FCT Project, PTDC/MAR/100348/2008 and European Space Agency projects DUE CoastColour (ESRIN/AO/1-6141/09/l-EC) and Climate Change Iniciative — Ocean Color (AO-1/6207/09/I-LG). The work has been also partially supported by the European Space Agency within the framework of the MERIS Validation Activities under contract n. 12595/09/I-OL, and sampling activities benefited from European projects HERMES (GOCE-CT-2005-511234) and Hermione (EC contract 226354) support. We would like to thank NASA OBPG for the MODIS data and ESA Project AOPT-2423 for providing MERIS full resolution images. Ana C. Brito was funded by a Portuguese Post-doc grant from FCT (BPD/63017/2009) and by the Investigador FCT Program (IF/00331/2013). Davide D'Alimonte was funded by Investigador FCT Program (IF/00541/2013). info:eu-repo/semantics/publishedVersion

The effect of high (ambient) and low (shaded to 50 % of ambient) light on microphytobenthic biofilm primary production, vertical migration and allocation of photoassimilated carbon into extracellular carbohydrates was investigated over the low tide emersion period at Sarilhos Pequenos on the Tagus estuary, Portugal, in July 2000. Carbon uptake ( 14 C measurements), electron transport (pulse-amplitude modulated [PAM]-fluorescence) and carbon allocation into extracellular carbohydrate fractions were measured. There was a decrease in the maximum rate of primary production (P max ) ( 14 C) over the emersion period (16 decreasing to 5 mg C m -2 h -1 at midday and the end of emersion, respectively) that was independent of the incident light and the light history to which the biofilms had been exposed. Primary production ( 14 C) did not correlate with measurements of in situ relative electron transport rate (rel.ETR), due in part to the light-induced migration of the cells away from the sediment surface during periods of high irradiance (photosynthetic photon flux density [PPFD] > 1200 mol m -2 s -1 ). Downward migration coincided with the light level at which P max ( 14 C) was reached, 750 mol m -2 s -1 , and with a point of inflexion on the rel.ETR versus PPFD curve. Above this light level rel.ETR was over-estimated due to migration of the cells into a lower light field in the sediment. Shading significantly increased the extracellular polymeric substance (EPS) production rate (from 0.4 to 1.0 mg C m -2 h -1 in ambient and shaded light, respectively) and percentage allocation of photoassimilates into EPS (from 4 ± 1.0 to 18 ± 3.5 % of total production in ambient and shaded light, respectively). In contrast, percentage allocation of photoassimilates to low molecular weight extracellular carbohydrate was higher in the non-shaded treatments (35 ± 4.5 % compared with 13 ± 3.8% in ambient and shaded treatments, respectively), probably due to photosynthetic 'overflow'. In non-shaded biofilms there was little or no increase in the concentration of all extracellular carbohydrate fractions until the last hour before tidal immersion. Results indicate that diel patterns in microphytobenthic primary production are not predictable solely from light data.

Recent global warming reduces surface water salinity around the Antarctic Peninsula as a result of the glacial meltwater runoff, which increases the occurrence and abundance of certain phytoplankton groups, such as cryptophytes. The dominance of this particular group over diatoms affects grazers, such as Antarctic krill, which preferentially feed on diatoms. Using three late summer data sets from the Bransfield Strait (2008–2010), we observed variations in the dominant phytoplankton groups determined by HPLC/CHEMTAX pigment analysis and confirmed by microscopy. Results indicate that the domi- nance of diatoms, particularly in 2008 and 2009, was associated with a deeper upper mixed layer (UML), higher salinity and warmer sea surface temperature. In contrast, cryptophytes, which were dominant in 2010, were associ- ated with a shallower UML, lower salinity and colder sea surface temperatures. The low diatom biomass observed in the summer of 2010 was associated with high nutrient concentration, particularly silicate, and low chlorophyll a (summer monthly average calculated from satellite images). The interannual variability here observed suggests a delayed seasonal succession cycle of phytoplankton in the summer of 2010 associated with a cold summer and a late ice retreat process in the region. This successional delay resulted in a notable decrease of primary producers’ biomass, which is likely to have impacted regional food web interactions. This study demonstrates the susceptibility of the Antarctic phytoplankton community structure to air temperature, which directly influences the timing of ice melting and consequently the magnitude of primary pro- duction and succession pattern of phytoplankton groups. This study was conducted within the activities of the SOS-CLIMATE (Southern Ocean Studies for Understanding Climate Changes Issues) project. This is a multidisciplinary program as part of the GOAL (Group of High Latitude Oceanography) activities in the Brazilian Antarctic Program, coordinated by SECIRM. Financial support was provided by CNPq (National Council for Research and Development). The authors thank the crew of the Brazilian Navy RV ‘‘Ary Rongel’’ and several investigators participating in the cruises for their valuable help during the collection of samples. We are grateful to Simon Wright, from the Australian Antarctic Division, for providing CHEMTAX v.1.95, to Ricardo Pollery for performing all nutrient analysis and to Nancy Tenenbaum for her helpful comments and revising the manuscript. C.R. Mendes and M.C. Leal were funded by a PhD grant (SFRH/BD/36336/2007 and SFRH/BD/63783/2009, respectively) funded by the Fundação da Ciência e Tecnologia (QREN-POPH-Type 4.1—Advanced Training, subsidized by the European Social Fund and national funds MCTES). A PhD fellowship from CAPES (Brazil) was granted to M.S.de Souza. V.M. Garcia and C.A. Garcia are granted with science fellowships from CNPq. published

Coastal and estuarine intertidal sediments are commonly colonized by dense populations of microphytobenthos. Due to wind and tides, important fractions of microphytobenthic populations may be buried. A mathematical model describing the depth variation of chlorophyll a in intertidal sediments was developed and experimentally tested. The model assumed first-order chlorophylla degradation and a constant mean burial velocity which resulted in a negative exponential variationC Z =C O exp{-k/vz} (C Z andC O =chlorophylla concentration at depth zand at the surface;k=specific degradation rate of chlorophyll a to pheopigments;V=mean burial velocity). Chlorophylla concentration depth profiles in different sediment types measured at the Tagus estuary and Ria Formosa (Portugal) were used to validate the model. The model was adjusted to field data. The chlorophyll a degradation rate was measured in a microcosm experiment under total darkness and no tidal action, and sampled during three months. This rate was shown to be independent of time and depth for the upper 0–15 mm depth interval. This result allowed the estimation ofV for each sampling site. Comparison of predicted and observed temporal data further confirmed the validity of the model andk andV values. Despite its simplicity, the proposed model adequately described the depth distribution of chlorophylla in different types of intertidal sediments. The model allowed the quantitative characterization of the buried microphytobenthic biomass (depth-integrated biomass) and the assessment of its importance as potentially productive stock of cells.

The Water Framework Directive (WFD) requires the assessment of ecological quality of water bodies based on physico-chemical and biological elements. This paper is focused on the use of phytoplankton as a biological indicator of ecological quality in Portuguese transitional waters (TWs). Phytoplankton is considered to be a sensitive indicator to environmental changes, especially nutrient enrichment, and is therefore useful for evaluating eutrophication processes. According to the WFD, three metrics should be generally considered to assess ecological status: phytoplankton biomass (chlorophyll a), phytoplankton composition and abundance, and phytoplankton bloom intensity and frequency. This work presents an integrated methodology that comprises the first and the last metrics indicated above, analyzed during the growing season (February–October). Significant (p

The composition and distribution of phytoplankton assemblages around the tip of the Antarctic Peninsula were studied during two summer cruises (February/March 2008 and 2009). Water samples were collected for HPLC/CHEMTAX pigment and microscopic analysis. A great spatial variability in chlorophyll a (Chl a) was observed in the study area: highest levels in the vicinity of the James Ross Island (exceeding 7 mg m−3 in 2009), intermediate values (0.5 to 2 mg m−3) in the Bransfield Strait, and low concentrations in the Weddell Sea and Drake Passage (below 0.5 mg m−3). Phytoplankton assemblages were generally dominated by diatoms, especially at coastal stations with high Chl a concentration, where diatom contribution was above 90% of total Chl a. Nanoflagellates, such as cryptophytes and/or Phaeocystis antarctica, replaced diatoms in open-ocean areas (e.g., Weddell Sea). Many species of peridinin-lacking autotrophic dinoflagellates (e.g., Gymnodinium spp.) were also important to total Chl a biomass at well-stratified stations of Bransfield Strait. Generally, water column structure was the most important environmental factor determining phytoplankton communities’ biomass and distribution. The HPLC pigment data also allowed the assessment of different physiological responses of phytoplankton to ambient light variation. The present study provides new insights about the dynamics of phytoplankton in an undersampled region of the Southern Ocean highly susceptible to global climate change. published

Estuarine microphytobenthos are frequently exposed to excessively high irradiances. Photoinhibition in microalgae is prevented by various photophysiological responses. We describe here the role of the xanthophyll pigments in photoacclimation. The pigment composition of the microphytobenthos was studied in three European estuaries (Barrow, Ireland; Eden, UK; Tagus, Portugal). Using HPLC-analyses, microscale changes in biomass and pigment composition were monitored over short (hourly) and long (seasonal) time scales. In the Barrow estuary, the biomass of microphytobenthos (measured as chlorophyll a) increased significantly in the top 400-500 µm of the sediment surface within 1 h of emersion; simultaneously, the xanthophyll pool size (diadinoxanthin plus diatoxanthin, dd + dt) almost doubled. A more gradual conversion of dd into dt was observed, with the dt:dd ratio increasing from 0.1 at the start of emersion to 0.3 after 3 h emersion. Similar trends in the dt:dd ratio were observed in the surface sediments of the Eden and the Tagus estuaries. Higher ratios were recorded in the Tagus estuary, which may be explained by higher incident irradiance. In addition, seasonal studies carried out in the Eden and Tagus estuaries showed that the xanthophyll pool size increased by 10% in the summer months. The pool size was highest in the Tagus estuary. Concurrently, high values for the de-epoxidation state were recorded, with values for dt/(dt + dd) 0.35 recorded in the summer. At the Eden, the ratio never exceeded 0.3. The de-epoxidation state was higher in winter than in summer, which was ascribed to the low winter temperatures. During a vertical migration study, a negative relationship between chlorophyll a and the de-epoxidation state was observed. It is suggested that this relationship originates from 'micro-migration' within the biofilm. Migration within the euphotic zone may provide an alternative means for cells to escape photodamage. In this paper, we propose that both xanthophyll cycling and 'micro'-migration play an important role in photoacclimation and it appears that these processes operate in parallel to regulate the photosynthetic response.

Microelectrode oxygen profiles were measured in intertidal sediments from Ria Formosa (S. Portugal), a very productive shallow coastal lagoon. Four intertidal sampling sites were selected according to different sediment characteristics. Individual profiles revealed a high degree of lateral variability on a centimeter spatial scale. Nevertheless, consistent differences were observed between oxygen profiles measured in atmosphere-exposed and inundated intertidal sediments: in organically poor sand oxygen-penetration depth varied from 3 mm in inundated cores to more than 7 mm in exposed ones, while in organically rich muddy sand and mud it remained between 0.5–2.0 mm. The oxygen input from inundated to exposed conditions was estimated for each sampling site. Semi-diurnal tidal fluctuation, leading to periodical atmospheric exposure of sediments plays a major role in the oxygenation process of intertidal zones of Ria Formosa.

The coccolithophores are a marine phytoplankton group that can play an important role in selective uptake of Cadmium (Cd) in neritic environments. Under project Cd-ToxCoN (PTDC/MAR/102800/2008) studies were conducted to investigate the in vitro reaction of Emiliania huxleyi to Cd exposure, namely changes in the crystal lattice of (cocco)liths, the calcite elements of the exoskeleton (coccosphere).Uni-algal cultures of E. huxleyi were obtained by multiple cell isolation from the same water sample collected from Portuguese offshore waters, during opportunity cruises (Portuguese Marine Navy). Several morphotypes of E. huxleyi are currently recognized. The identification of the morphotype of E. huxleyi from Portuguese coastal waters was done by morphological analysis of the exoskeleton using scanning electron microcopy (JEOL JSM-5200LV and FEG-SEM JEOL 7001F) and by DNA sequencing of tufA gene following.Experiments were conducted in batch cultures grown in enriched sea-water medium (K/10) under constant environmental conditions (14h L: 10h D, 15ºC, 40 µmol photons m-2 s-1). At the exponential growth phase, 3 replicate E. huxleyi cultures were subject for 48h to Cd concentrations of 10 µgL-1 and 100 µgL-1, two and three orders of magnitude above average marine concentration values respectively. In each case three additional replicate cultures with no Cd added were used as control.The effect of Cd was evaluated by measuring in vivo fluorescence (ratio of variable (Fv) to maximum (Fm) fluorescence) (Water PAM fluorometer – Walz) and by detailed morphometric analysis of coccospheres and liths performed on SEM micrographs. The parameters measured are those presented in Figure 1. Malformed, damaged or tilted liths were not measured.Morphological observations of the coccosphere and liths and DNA sequencing allowed the identification of the isolated strains of E. huxleyi as morphotype A. Results on the Cd exposure experiments indicate that E. huxleyi type A seems to tolerate high concentrations of Cd. Despite the very high concentration of Cd tested no lethal limit was reached and Fv/Fm values recorded after 48h at 10 µgL-1 Cd (0.607±0.008) and 100 µgL-1 Cd (0.603±0.008), very similar to the values recorded in the control cultures (0.642±0.016 and 0.636±0.018, respectively) and before Cd addition (0.642±0.012 and 0.636±0.007, respectively).Regarding the different morphometric parameters analysed on coccospheres and liths, no significant measurable effects were observed. However, we observed, in response to increasing Cd concentration, an increasing number of liths with fused or partially fused elements (Fig. 2) suggesting a higher calcification of liths. This interpretation is supported by the results of the analysis of coccosphere calcium content. Cultures exposed to Cd presented a higher Ca content compared to control cultures. The highest values were recorded in coccospheres submitted to 100 µg.L-1 of Cd representing a 65% increase in Ca content in comparison to control coccospheres.E. huxleyi is ubiquitous in present day oceans and usually very tolerant to culture conditions and is thus frequently used as a model species in the study of coccolithophores. These same characteristics may also justify the observed high tolerance to Cd. Studies with other species are needed to clarify if the surprising resistance to Cd is unique to E. huxleyi or characteristic of other unicellular algae with calcium carbonate shells.This work was funded by projects PEst-OE/Mar/UI0199/2011, Pest/OE/CTE/UI/0263 and PTDC/MAR/102800/20082

The Tagus Estuary is one of the largest estuaries in Europe and merges large urban and industrial areas. Understanding phytoplankton community variability is key for an appropriate assessment of the estuarine ecological status. The objective of the present study was to assess the importance of the tidal influence over the phytoplankton community and to evaluate its main drivers of variation. Weekly sampling was performed at two stations on the Tagus Estuary with different anthropogenic pressures (Alcântara and Barreiro). The sampling covered periods with different tidal amplitude. Alcântara presented both the lowest and highest concentrations of dissolved inorganic nitrogen (DIN) and orthophosphate concentration (DIP), depending on the tidal height. Such high variability in this sampling station is probably due to its proximity to a sewage treatment station outfall and to the estuary mouth. In the present study, both seasonal and tidal variations influenced the chlorophyll a concentration of which the tidal cycle explained up to 50% of the chlorophyll a variations. Chlorophyll a displayed a seasonal trend with two peaks of phytoplankton biomass between spring and mid-summer. The main drivers of chlorophyll a variation were radiation, water temperature, tidal amplitude, salinity, river discharge, and the inorganic nutrients DIN and DSi. The estuarine phytoplankton community was mainly dominated by Bacillariophyceae, especially at Alcântara. Bacillariophyceae were less important at Barreiro, where communities had a higher representation from other phytoplankton groups, such as Cryptophyceae and Prasinophyceae. The drivers of variability in the community composition were similar to those influencing the total biomass. In conclusion, the spring-neap tidal cycle strongly influenced the phytoplankton community, both in terms of biomass and community composition. Of the several tidal conditions, spring tides were the tidal condition that presented both higher biomass and higher Bacillariophyceae representativity in the community.

Dissolved nitrogen fluxes and denitrification were studied during 1 yr in intertidal sediments of the Tagus estuary (Portugal). This study focused on the factors regulating both nitrogen fluxes across the sediment-water interface and denitrification, and on the effect of microphytobenthos activity in controlling nitrogen cycling in these areas. Sampling was performed monthly at 2 stations located in inner and outer intertidal areas. Fluxes of O 2 , NO 3 - , NO 2 - , NH 4 + and N 2 O, and denitrification (determined by the nitrogen-isotope pairing technique) were measured simultaneously in closed chambers incubated in the laboratory under simulated in situ temperature and light conditions, as well as in the dark. At the sediment-water interface, higher DIN fluxes and lower denitrification rates were registered at higher temperatures and lower NO 3 - concentration in the water column. Oxygen uptake by the sediment was generally higher than release, particularly in summer. Primary productivity displayed a seasonal cycle, positively influenced by temperature. Denitrification rates were closely related to NO 3 - river-input, Temperature, NO 3 - concentration in the water column, microphytobenthos, infauna and tidal height were the key parameters involved in controlling nitrogen cycling at the sediment-water interface in the Tagus estuary. A comparison of annual nitrogen fluxes and denitrification rates between sites was made, taking into account tidal immersion periods. Hence, N-removal by denitrification accounted for 156 mmol m -2 yr -1 in the inner station and 482 mmol m -2 yr -1 in the outer station. These rates represent respectively ca 3 and 9% of total DIN available in the estuarine water column at those 2 stations, respectively. N 2 O production was comparatively very low (0.3 to 0.6 mmol m -2 yr -1 ). The estimated nitrogen assimilation rates by microphytobenthos were 707 mmol m -2 yr -1 in the inner station and 333 mmol m -2 yr -1 in the outer station, indicating that a considerable amount of nitrogen was retained within benthic microalgae. The assimilation/denitrification ratio, with a mean value of 2, shows the relative importance of the denitrification role as a N-sink. Apart from denitrification, it is suggested that other processes must be involved in the removal of nitrogen from the estuary.

Monitoring lakes in high-latitude areas can provide a better understanding of freshwater systems sensitivity and accrete knowledge on climate change impacts. Phytoplankton are sensitive to various conditions: warmer temperatures, earlier ice-melt and changing nutrient sources. While satellite imagery can monitor phytoplankton biomass using chlorophyll a (Chl) as a proxy over large areas, detection of Chl in small lakes is hindered by the low spatial resolution of conventional ocean color satellites. The short time-series of the newest generation of space-borne sensors (e.g., Sentinel-2) is a bottleneck for assessing long-term trends. Although previous studies have evaluated the use of high-resolution sensors for assessing lakes&rsquo, Chl, it is still unclear how the spatial and temporal variability of Chl concentration affect the performance of satellite estimates. We discuss the suitability of Landsat (LT) 30 m resolution imagery to assess lakes&rsquo, Chl concentrations under varying trophic conditions, across extensive high-latitude areas in Finland. We use in situ data obtained from field campaigns in 19 lakes and generate remote sensing estimates of Chl, taking advantage of the long-time span of the LT-5 and LT-7 archives, from 1984 to 2017. Our results show that linear models based on LT data can explain approximately 50% of the Chl interannual variability. However, we demonstrate that the accuracy of the estimates is dependent on the lake&rsquo, s trophic state, with models performing in average twice as better in lakes with higher Chl concentration (&gt, 20 &micro, g/L) in comparison with less eutrophic lakes. Finally, we demonstrate that linear models based on LT data can achieve high accuracy (R2 = 0.9, p-value &lt, 0.05) in determining lakes&rsquo, mean Chl concentration, allowing the mapping of the trophic state of lakes across large regions. Given the long time-series and high spatial resolution, LT-based estimates of Chl provide a tool for assessing the impacts of environmental change.

Reliable satellite estimates of chlorophyll-a concentration (Chl-a) are needed in coastal waters for applications such as eutrophication monitoring. However, because of the optical complexity of coastal waters, retrieving accurate Chl-a is still challenging. Many algorithms exist and give quite different performance for different optical conditions but there is no clear definition of the limits of applicability of each algorithm and no clear basis for deciding which algorithm to apply to any given image pixel (reflectance spectrum). Poor quality satellite Chl-a data can easily reach end-users. To remedy this and provide a clear decision on when a specific Chl-a algorithm can be used, we propose simple quality control tests, based on MERIS water leaving reflectance (ρw) bands, to determine on a pixel-by-pixel basis if any of three popular and complementary algorithms can be used. The algorithms being tested are: 1. the OC4 blue-green band ratio algorithm which was designed for open ocean waters; 2. the OC5 algorithm which is based on look-up tables and corrects OC4 overestimation in moderately turbid waters and 3. a near infrared-red (NIR-red) band ratio algorithm designed for eutrophic waters. Using a dataset of 348 in situ Chl-a / MERIS matchups, the conditions for reliable performance of each of the selected algorithms are determined. The approach proposed here looks for the best compromise between the minimization of the relative difference between In situ measurements and satellite estimations and the number of pixels processed. Conditions for a reliable application of OC4 and OC5 depend on ρw412/ρw443 and ρw560, used as proxies of coloured dissolved organic matter and suspended particulate matter (SPM), as compared to ρw560/ρw490, used as a proxy for Chl-a. Conditions for reliable application of the NIR-red band ratio algorithm depend on Chl-a and SPM. These conditions are translated into pixel-based quality control (QC) tests with appropriately chosen thresholds. Results show that by removing data which do not pass QC, the performance of the three selected algorithms is significantly improved. After combining these algorithms, 70% of the dataset could be processed with a median absolute percent difference of 30.5%. The QC tests and algorithm merging methodology were then tested on four MERIS images of European waters. The OC5 algorithm was found to be suitable for most pixels, except in very turbid and eutrophic waters along the coasts where the NIR-red band ratio algorithm helps to fill the gap. Finally, a test was performed on an OLCI-S3A image. Although some validations of water reflectance are still needed for the OLCI sensors, results show similar behavior to the MERIS applications which suggests that when applied to OLCI data the present methodology will help to accurately estimate Chl-a in coastal waters for the next decade.