Investigations into the phytoplankton of the Bay of Biscay in July 2006 revealed an extensive bloom of an unidentified haptophyte species. High-resolution sampling techniques identified the region in the vicinity of the mouth of the Loire estuary as an area of high (106–107cellsl−1) cell densities of the haptophyte in a thin sub-surface layer. This organism dominated the phytoplankton population regionally. Measurements of the vertical distribution of horizontal shear showed that the population, located at ca. 20m depth, was confined to a layer lying between two density discontinuities with high shear. Physical measurements indicated that the population was being advected southeastwards, along the coast. Seaward spreading of the population was also noted during the survey. Horizontal diffusion could be derived from the changes in the offshore gradient in the population's distribution with time, with estimates of Kx, the horizontal diffusion coefficient, of the order of 100m2s−1. The magnitude of horizontal dispersion is compared with that of horizontal advective flux, vertical dispersion and growth.

High-resolution physical and biological measurements were carried out in May–June 2007 during the ‘HABIT-Pontevedra 2007’ survey in Ría de Pontevedra (Galician Rías Baixas, NW Spain) to study small-scale physical–biological interactions in the distribution of microphytoplankton, with special emphasis on harmful species. Longitudinal transects from the Ría to the adjacent shelf were sampled to describe the spring–neap tidal and circadian variability. An in situ particle profiler, a moored ADCP, and a towed undulating CTD (Scanfish) were used during the survey, which took place after an upwelling pulse at neap tides during a downwelling–upwelling cycle and coincided with the annual maximum of Pseudo-nitzschia spp. Cell maxima of Pseudo-nitzschia seriata (2×106cellsL−1) and Pseudo-nitzschia delicatissima (6×105cellsL−1) groups were observed during the first half of the cruise during downwelling, and a significant decrease in cell numbers occurred during subsequent relaxation-upwelling conditions. Thin layers were eroded during downwelling and formed again in the subsequent upwelling pulse. Cells of the P. seriata group were always dominant in terms of biomass but the contribution of the P. delicatissima group increased with stratification. Water exchange between the Ría and the adjacent shelf was mainly controlled by the upwelling/downwelling cycle, and tidal (both semidiurnal and spring–neap) variability appeared as a modulation of the response of the Ría circulation to wind variability. The circadian variability was regulated by tidal forcing, and Pseudo-nitzschia spp. maxima were associated with high stratification during low tide. The magnitude of spring–neap tidal and circadian variability has to be considered when designing and implementing water quality and harmful algae monitoring programmes. Blooms of Pseudo-nitzschia ssp. were not associated with the occurrence of domoic acid in shellfish even when Pseudo-nitzschia australis was dominant. These results confirm that just cell densities of the potential toxin producer are not enough for early warning in monitoring of Pseudo-nitzschia events.

An investigation into the distribution of Dinophysis spp. in coastal waters off the south coast of Ireland was carried out in July 2007. Dinophysis acuta was present as a sub surface layer containing up to 55,000 cells L-1. The population had a high percentage of viable cells (mean: 89%; median: 94%; n = 24) with a high specific division rate (similar to 0.55 d(-1)). The layer, of approximately 5 m thickness, did not coincide with the fluorescence maximum and was present as a patch of horizontal dimension less than 10 km x 7 km. Both conventional and towed undulating CTD used in conjunction with high vertical resolution sampling methods showed the patch of Dinophysis to move with a similar speed and direction as the coastal flow, which ran parallel to the coast in the form of a coastal jet with speed of the order of 6.5-7 km day(-1). The implications of the alongshore transport of populations of harmful species in coastal jets for monitoring programmes and predictive models are discussed. (C) 2011 Elsevier B.V. All rights reserved.

Recent advances in laser and video technologies have enabled single particles to be visualized in aqueous solution. Here, we describe a new instrument enabling the analysis of the fluorescence signatures of marine particles directly in seawater: the Video Fluorescence Analyser (VFA). A field of view is produced inside a measurement chamber by a laser beam at 473 nm that illuminates a shallow region, 3500 µm deep. Individual cells or particles in this field appear as individual spots of light, which are clearly resolved by video against a dark background. The method can resolve particles ranging from 6 µm to several millimeters. The camera is equipped with mobile optical filters: band‐pass filter, 520–580 nm, for phycoerythrin visualisation and high‐pass filter, > 600 nm, for Chlorophyll a pigment. These filters are remotely controlled and displaced in front of the CCD camera, allowing imaging and discrimination between fluorescent particles. We report here experimental procedures and calibrations performed in the laboratory with phytoplankton cells (Dunaliella tertiolecta, Karenia mikimotoi, Pseudonitzschia australis) and calibrated fluorescent beads. Image analysis processing enabled particle counts, measurements, and size classification. The auto‐fluorescence of individual particles was also tested in situ during a field cruise. In relation to other sensors, the VFA allowed particle enumeration and discrimination and detecting spatial variability of the phytoplankton size spectra in relation to hydrology. The results indicate that fluorescence/video analysis techniques can be easily used in the laboratory or at sea for direct in situ visualization and analyses of phytoplankton populations.

A new in situ probe which allows direct determination of the particles distribution spectra in the sea as weil as an unbiased estimation of the total particle load, has been developed by IFREMER. It has been used in eoastal areas and the results give new insights into environmental eoastal proeesses whieh are described. This new sensor uses the well-known prineiple of diffraetion pattern analysis previously used in bench-top instruments. However, the rigourous eonstraints imposed by its oeeanographic uses required a completely new design. This instrument presents numerous advantages in environmental research. Its use in phytoplankton studies is presented and led to a new sampling strategy for toxie dinoflagellates. It allows to study sedimentation and floceulation proeesses. Finally, sampling of hydrophobie pollutants may be optimized by means of particles population clustering .

Dinophysis is the most harmful toxic phytoplankton on the French coast in terms of its impact on local economy and public health. In Arcachon Bay, Dinophysis spp. have periodically affected shellfish industry for the last ten years; the most important events are analysed in detail in this paper. Regular monitoring revealed that these events originated outside Arcachon Bay in the open ocean. Data from 14 surveys and two coastal networks showed that Dinophysis was primarily found in the vicinity of Capbreton, 100km south of the mouth of Arcachon Bay. The Dinophysis distribution on the continental shelf was determined during two surveys in 2005 and 2008: the highest concentrations were located along the coast and reached 18000cells.L−1. Analysis of available current data revealed that strong westerlies lead to northward currents of up to 19cm.s−1. These marine meteorological conditions were frequently observed just prior to Dinophysis events and lead us to suggest that northward currents transport Dinophysis from the Capbreton area to Arcachon Bay.

The distributions of Dinophysis acuminata, its potential prey Myrionecta rubra, and the microplankton populations associated with them, were studied in Ria de Pontevedra (NW Spain) dur- ing a 2 wk cruise that covered an upwelling-downwelling cycle, and during intensive sampling over 21 h at the end of the cruise. Special attention was focused on the characterization and physiological condition of D. acuminata. There was vertical segregation between a phytoplankton assemblage that was dominated by upwelling-promoted diatoms and another assemblage that was dominated by small dinoflagellates located in the warmer surface layer (0 to 5 m) where D. acuminata was observed. High spatio-temporal variability was observed in the frequency of cells containing starch granules (indicating photosynthetic activity) and digestive vacuoles (indicating heterotrophic feed- ing); this pattern corresponded with the apparent availability of M. rubra cells. Populations of D. acuminata and M. rubra have their own niches and distinct responses to physical forcing, but both are located in common water masses and occasionally meet. Changes in vacuolation of D. acuminata were followed by a substantial increase (~35%) in cellular volume. D. acuminata did not exhibit daily migratory behaviour, and expressed a high division rate (0.51 d -1 ) under downwelling conditions. This work sheds new light on the relation between D. acuminata populations and its potential prey, and on its ecophysiology; it also questions previous assumptions about the environment that is suitable for its development.

During a 10 day survey in the CelticSea near the Irish South-West coast (July 2007), Dinophysis acuta was observed in large numbers. The deployment of a profiler allowed for the identification of a D. acuta thin layer that reached 1910 cells/L The aim of the study was to investigate if the bloom that occurred in low light environment was viable, dividing, actively producing toxins and if the toxin profile changed over a short term period. Several large concentrates of phytoplankton samples were obtained over a 14 h period, from evening to morning, by pumping Dinophysis from specific depths. In addition, D. acuta was collected in complete darkness at 81 m depth by concentrating 120 L of water. The cells were extracted and their toxin profiles were established by liquid chromatography - mass spectrometry (LC-MS). Passive samplers were deployed in a nearby location for 6 days at 30, 50, 70 and 110 m depth, and the toxin profiles were determined by LC-MS as above. The toxin profiles obtained in phytoplankton samples and in the SPATT were compared and correlated well. Sample concentrates and SPATT results suggested that toxic D. acuta occurred and produced similar toxin profiles at all water depths, including below the euphotic zone. (C) 2010 Elsevier Ltd. All rights reserved.

During May-June 2005, a 17-d cruise was carried out in Ria de Pontevedra (Galician Rias Baixas) to study the physical-biological interactions that may lead to subsurface aggregations of phytoplankton organisms in thin layers (TLs). Physical processes governed the initiation and development, maintenance, and decline of a diatom (toxin producing Pseudo-nitzschia spp. and Chaetoceros socialis) TL during an upwelling relaxation-upwelling-downwelling sequence. Differences in shear profiles appeared to lead to the formation of a TL during upwelling events. These results reveal that the coupling between maximum values of shear and buoyancy frequency can shape a subsurface chlorophyll maximum (SCM) into a TL. The effect of shear upon phytoplankton patches, which has been predicted on the basis of theoretical studies, has been corroborated in this study in which the vertical distribution of an observed TL was controlled by physical processes.Understanding both local fine-scale circulation patterns and regional physical processes will improve our knowledge of the spatial and temporal occurrence of these layers. Results here bring new understanding in TL dynamics at coastal upwelling sites and provide information about the physical processes involved in TL development, which can be used to predict their occurrence and understand their ecological implications. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract Domoic acid (DA) is a potent toxin produced by bloom-forming phytoplankton in the genus Pseudo-nitzschia, which is responsible for causing amnesic shellfish poisoning (ASP) in humans. ASP symptoms include vomiting, diarrhea, and in more severe cases confusion, loss of memory, disorientation, and even coma or death. This paper describes the development and validation of a rapid, sensitive, enzyme linked immunosorbent assay test kit for detecting DA using a monoclonal antibody. The assay gives equivalent results to those obtained using standard high performance liquid chromatography, fluorenylmethoxycarbonyl high performance liquid chromatography, or liquid chromatography—mass spectrometry methods. It has a linear range from 0.1–3 ppb and was used successfully to measure DA in razor clams, mussels, scallops, and phytoplankton. The assay requires approximately 1.5 h to complete and has a standard 96-well format where each strip of eight wells is removable and can be stored at 4°C until needed. The first two wells of each strip serve as an internal control eliminating the need to run a standard curve. This allows as few as 3 or as many as 36 duplicate samples to be run at a time enabling real-time sample processing and limiting degradation of DA, which can occur during storage. There was minimal cross-reactivity in this assay with glutamine, glutamic acid, kainic acid, epi- or iso-DA. This accurate, rapid, cost-effective, assay offers environmental managers and public health officials an effective tool for monitoring DA concentrations in environment samples.

Intertidal mudflats are important nursery grounds for juveniles of many fish species. However, they are being used increasingly to farm bivalve molluscs, which produce large amounts of organic “fluff”, overlying the mud. Fish such as sole, Solea solea , hide in this fluff from potential predators, but the energy consumed by respiring the fluff may be high due to its biorheological properties. We developed an ichthyoviscometer. It incorporates a freshly killed fish as a viscometer, and we developed it to measure the rheological properties of fluids and suspensions, including fluff, at scales encompassing those in gill ventilation. We have shown that the rheological behaviour of fluff is close to that of a gel with a yield stress strongly dependent on particulate organic matter concentration ([POM]). This has allowed us to model fluff flow through the gill channels in living sole as a function of fish size and [POM], showing that in a 26-g sole, fluff would halve flow at a [POM] value of 3.2 g l −1 , and stop it at 3.4.

Despite its rarity, Dinophysis acuminata is in terms of economic impact, the first toxic algal species along the coasts of Western Europe. It is observed at low levels (< 20 cell l(-1)) all the year round but toxic events occur mainly in late spring and summer. D. acuminata ecophysiology is largely unknown due to the inability to culture it. Therefore, standard biomass models based on inorganic nutrition are largely inadequate. Presently, any progress in describing the conditions of population growth of this species will be a step forward to prediction of harmful events at the coast. This species has been observed at increased, albeit low cell densities in retentive eddies located in pycnocline layers. A concentration build-up of one species results from the balance between growth and loss processes, one of the latter being dispersal. The scales of interest for a D. acuminata population are of the order of 10 nautical miles on the horizontal and duration of 10 days, for a reported achievable growth rate of 0.6 day(-1). A three dimensional (3D) hydrodynamical model of the Bay of Biscay has been elaborated to reproduce hydrological structures over the last decade. We attempt here to relate the existence of retentive structures revealed from simulations under realistic forcing conditions and the toxic coastal events recorded in the 10-year time series of the French plankton monitoring network database. The eddies in the coastal area appear to be directly related with the Dinophysis coastal events and they may be a potential effective tool to predict those. (c) 2006 Elsevier B.V. All rights reserved.

Blooms of Dinophysis in French coastal waters are implicated in most bans on marketing commercial bivalves. However, the relation between Dinophysis cell density and shellfish toxicity is not always consistent. Discrepancies may be due to the simple fact that it is nearly impossible to compare an integral over a few days (shellfish toxin content) and water samples. Furthermore, it seems that cells may have a variable specific toxicity. This work focuses on the variability in cell toxicity taking into account recent findings and using liquid chromatography coupled to mass spectrometry with an ion trap and electrospray interface. Esterified analogues of okadaic acid (DTX-4 and diol-esters) have been identified in cultures of Prorocentrum lima, another okadaic acid producer. These analogues are inactive on some protein phosphatases, contrary to okadaic acid, and seem to protect the cell from harmful effects by the toxin and to be enzymatically hydrolyzed during cell lysis. In order to document specific toxicity and to validate the presence of these analogues, D. acuminata concentrates were subjected to two separate heating and freeze/thaw procedures, respectively inhibiting or promoting hydrolysis. This paper reports on the high variability of D. acuminata specific toxicity and the presence of esters found in half of the samples only.

HarmfulAlgal Blooms Figure 1.Many HABs produce vividly colored blooms of cells that accumulate on surface water.Th ese high biomass blooms can cause hypoxia, can contribute to toxicity of fi sh and shellfi sh, and can cause other environmental problems.Main photo: A bloom off Heron Island, Australia caused by cyanobacteria (Trichodesmium theibautii).Photo by P. Glibert.Insets: (Left) A bloom in Hong Kong, China caused by caused by dinofl agellates (Gymnodinium sp.).Photo by M. Dickman.(Middle) A bloom in the Choptank River, one of the tributaries of the Chesapeake Bay, USA caused by dinofl agellates (Prorocentrum minimum).Photo by P. Glibert.(Right) A bloom in the Baltic Sea caused by caused by cyanobacteria (Anabaena sp.).Photo by K. Kononen.

In order to study the occurrence of Gymnodinium mikimotoï bloom on the French Atlantic coast, a three-dimensional model of primary production was set up. The biological model was coupled to a hydrodynamic model previously developed at Ifremer, by the intermediary of transport, diffusion and heat fluxes. The cycles of three limiting elements for the phytoplankton growth were modelised: nitrogen, phosphorus and silicon. The second phase of the study aimed at reproducing the summer dinoflagellate blooms. In this new approach a model of the species Gymnodinium mikimotoï was coupled with the previous biomass model which provides the physical and chemical environments. The study focuses on the results obtained by this specific sub-model. The parametrisation was based on some physiological studies reported from laboratory cultures and on parameters existing in the literature. Consistent with the observations, the model reproduces the sub-surface cell concentrations, in the zone of minimal turbulence. The formulation retained for the temperature effect on the growth rate leads to a strong influence of temperature on the onset of the bloom and the mortality rate controls the vertical distribution. Nevertheless, as formulated here, the model underestimates the cell density.