Les efflorescences à Dinophysis, microalgues productrices de toxines diarrhéiques, présentent la particularité d’être peu denses et les plus fortes concentrations observées sont souvent liées à des couches fines et stratifiées.

Elles ont pu être mises en évidence par le développement d’une instrumentation adaptée permettant de visualiser et cibler les couches d’eau à échantillonner :

  • POCKET PC étanche pour les embarcations légères
  • profileur pélagique avec vidéo-fluo-microscope
  • préleveur étagé

cf. figure ci-dessous (Velo Suarez Lourdes et al; 2008 ACL ; Farell et al, 2012, ACL).

Une autre caractéristique de Dinophysis est son cycle de vie (Reguera et al., 2012) avec une mixotrophie mise en évidence depuis quelques années. La culture de Dinophysis est devenue possible en y intégrant les proies qu’elle ingère, un cilié Myrionecta rubra, elles-mêmes cultivées à partir de Cryptophycées. Des expériences sur la mobilité verticale de Dinophysis en fonction d’extraits de Myrionecta ont aussi été réalisées avec l’IEO (Espagne) qui possédait des cultures de Dinophysis sp. en milieu contrôlé. Les premiers résultats montrent une grande variabilité dans les comportements des cellules en fonction de leur état physiologique et des cultures de Dinophysis très sensibles aux manipulations. L’étude et la modélisation du transport de Dinophysis, ont été démarrées au sein d’un projet européen FP7 (ASIMUTH, post-doctorat L. Vélo-Suarez) avec une approche lagrangienne (Vélo-Suarez et al, 2010).

Financement / Collaborations 

Université Bordeaux I (thèse en cours), Marine Institute, IEO Vigo, IOW, contrat européen HABIT (Harmful Algal Blooms in Thin Layers) collaborations avec Martin Ryan Institute (Irlande), IEO Vigo, CEFAS (Royaume Uni), et l'Université Johns Hopkins (USA)

Publications récentes 

Harmful Dinophysis species: A review

Auteurs : Beatriz Reguera, Lourdes Velo-Suárez,Robin Raine,Myung Gil Park
Reference : Harmful AlgaeVolume 14, February 2012, Pages 87–106, doi.org/10.1016/j.hal.2011.10.016
Keywords : Dinophysis, Diarrheic Shellfish Poisoning, Population dynamics, Monitoring

Scales characterising a high density thin layer of Dinophysis acuta Ehrenberg and its transport within a coastal jet

Auteurs : Farrell Hazel, Gentien Patrick, Fernand Liam, Lunven Michel, Reguera Beatriz, Gonzalez-Gil Sonsoles, Raine Robin
Reference : Harmful Algae, 15, 36-46. Publisher's official version : http://dx.doi.org/10.1016/j.hal.2011.11.003 , Open Access version : http://archimer.ifremer.fr/doc/00064/17538/


Application of a 3D Lagrangian model to explain the decline of a Dinophysis acuminata bloom in the Bay of Biscay

Auteurs : Velo Suarez Lourdes, Reguera B., Gonzalez-Gil Sonsoles, Lunven Michel, Lazure Pascal, Nezan Elisabeth, Gentien Patrick
Reference : Journal Of Marine Systems, 83(3-4), 242-252. http://dx.doi.org/10.1016/j.jmarsys.2010.05.011

Thin layers of Pseudo-nitzschia spp. and the fate of Dinophysis acuminata during an upwelling-downwelling cycle in a Galician Ria

Auteurs : Velo-Suarez L., Gonzalez-Gil S., Gentien P., et al
Reference : Limnol. Oceanogr. 53, 5, 1816-1834

Résumé : Fine-resolution measurements of phytoplankton and physical parameters were made from 31 May to 14 June 2005 in the Ria de Pontevedra (Spain), which is subject to seasonal upwelling. The main objective of this work was to elucidate physical-biological interactions leading to subsurface aggregations of toxin-producing microalgae (Pseudo-nitzschia spp. and Dinophysis spp.). A sequence of upwelling-relaxation-upwelling-downwelling events was recorded with a moored Acoustic Doppler Current Profiler (ADCP). Thin layers (TLs) of Pseudo-nitzschia spp. and other diatoms (up to 30 mu g chlorophyll a L-1) developed and persisted in the pycnocline above cooler (12.5 degrees C) upwelled water but were vertically displaced and even dispersed during downwelling. The establishment of steep pycnoclines after upwelling pulses and the formation of TLs of Pseudo-nitzschia spp. and other diatoms suggest that pycnoclines may act as retention areas for these populations. Their vertical displacement during downwelling would explain different patterns observed in the contamination of benthic resources and raft-mussels. A decimeter-scale segregation of Pseudo-nitzschia micans and Dinophysis acuminata populations was observed. The population of D. acuminata, present since March 2005 in Ria de Pontevedra, was never found within the pycnocline, did not perform any significant vertical migration, and was not dispersed during upwelling. Instead, it formed patches (up to 8 x 10(3) cell L-1) in the warmer (15-18 degrees C) surface (0-4 m) waters associated with a diurnal thermocline, and it spread throughout the ria into a near-surface layer during relaxation and downwelling. These results demonstrate the importance of considering species-specific behavior to predict the location of cell maxima.

GEOHAB. Core Research Project HABs in stratified systems

Auteurs : Gentien P. et al.
Reference : GEOHAB. Core Research Project HABs in stratified systems, IOC and SCOR, 59 pp.

Motility and autotoxicity in Karenia mikimotoi (Dinophyceae)

Auteurs : Gentien P., Lunven M., Lazure P., et al.
Reference : Phil. Trans. Royal Soc. B: 362, 14871937-1946.

Small scale retentive structures and Dinophysis

Auteurs : Xie H.Q., Lazure P., Gentien P.
Reference : J. Mar. Sys.: 64,1-4,173-188
Doi : 10.1016/j.jmarsys.2006.03.008

Résumé : 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.