Estudio fisiológico de Dinophysis spp. durante un ciclo de afloramiento/hundimiento en la Ría de Pontevedra

HABITFloraciones Algales Nocivas en Capas Fina

Climate Variability and Oceanographic Settings Associated with Interannual Variability in the Initiation of Dinophysis acuminata Blooms

In 2012, there were exceptional blooms of D. acuminata in early spring in what appeared to be a mesoscale event affecting Western Iberia and the Bay of Biscay. The objective of this work was to identify common climatic patterns to explain the observed anomalies in two important aquaculture sites, the Galician Rías Baixas (NW Spain) and Arcachon Bay (SW France). Here, we examine climate variability through physical-biological couplings, Sea Surface Temperature (SST) anomalies and time of initiation of the upwelling season and its intensity over several decades. In 2012, the mesoscale features common to the two sites were positive anomalies in SST and unusual wind patterns. These led to an atypical predominance of upwelling in winter in the Galician Rías, and increased haline stratification associated with a southward advection of the Gironde plume in Arcachon Bay. Both scenarios promoted an early phytoplankton growth season and increased stability that enhanced D. acuminata growth. Therefore, a common climate anomaly caused exceptional blooms of D. acuminata in two distant regions through different triggering mechanisms. These results increase our capability to predict intense diarrhetic shellfish poisoning outbreaks in the early spring from observations in the preceding winter

Spring-neap tidal and circadian variability in the distribution of two groups of Pseudo-nitzschia species in an upwelling influenced estuary

High-resolution physical and biological measurements were carried out in the Ría de Pontevedra (NW Spain) in late spring during the ‘HABIT Pontevedra 2007’ survey, which utilized high vertical resolution instruments. Cell maxima of P. delicatissima (6 x 105 cells L-1) and P. seriata (2 x 106 cells L-1) groups were observed during the first half of the cruise during downwelling and a significant decrease in cell numbers occurred during subsequent upwelling conditions. The effect of tidal (both semidiurnal and spring-neap) and event driven (upwelling-downwelling cycle) variability were evident. The observed sequence of events suggests that Pseudo-nitzschia populations were advected from the shelf. The circadian variability was regulated by tidal forcing and Pseudo-nitzschia spp. maxima were observed at low tide. From results presented here we conclude that the magnitude of spring-neap tidal and circadian variability has to be considered when designing and implementing harmful algal bloom monitoring programmesEn prens

Hydrodynamic conditions associated with the formation, maintenance and dissipation of a phytoplankton thin layer in a coastal upwelling system

During May–June 2005, a 17-d cruise was carried out in Ría de Pontevedra (Galician Rías 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.N

Ecological and physiological studies of Dinophysis spp. during an upwelling/downwelling cycle in Ría de Pontevedra (NW Spain)

Floraciones Algales Nocivas en Capas FinasHABI

Vertical distribution of division rates in coastal dinoflagellate Dinophysis spp. populations: implications for modelling

Publicado

Phased cell division, specific division rates and other biological observations of Dinophysis populations off the south coast of Ireland

The proportions of viable cells ofDinophysisspp. that were paired (dividing) and recently divided during a cell cycle were measured on populations ofD. acutaandD. acuminataobserved off the south coast of Ireland in July 2007 and July 2009. Both species exhibited phased cell division in 2009 with maximum frequency of division (fmax) 2 h after sunrise. Different patterns of division (timing offmax) were shown by D. acutain 2007, when the population aggregated in a thin layer was transported by a coastal jet flow. High resolution (decimetre-scale) profiles within the thin layer showed large differences in the vertical distribution of biological properties (feeding status, mortality). Values of the specific growth ratemwere compared to estimates derived in similar fashion from observations onDinophysispopulations elsewhere. Different patterns exhibited by the same species in different regions may be attributed to adaptations to latitudinal differences (length of photoperiod). The question of whether phased cell division always occurs inDinophysispopulations, and the incorporation of the potential specific division rate into models of Dinophysisgrowth are discussed. Comprehensivefield data sets demonstrate the impact of the results on the coherence of Dinophysispopulations during their transport along the Irish coast in jet-likeflows towards sites of intensive shellfish cultureVersión del editor

The growth season of Dinophysis acuminata in an upwelling system embayment. A conceptual model based on in situ measurements

The distribution and physiological condition of the DSP-toxin producerDinophysis acuminata, its relation with accompanying microplankton populations and coupling with upwelling events are described based on weekly sampling at afixed station in Ría de Pontevedra, Galician Rías Baixas, NW Spain between March and December 2007.D. acuminatawas detected from 18 June to 01 October. The appearance of D. acuminatain the Ría coincided with an upwelling-relaxation event and a short-lived maximum (up to 27 000 cells L −1 ) of its potential prey, the phototrophic ciliateMesodiniumcfrubrum. An increase in the proportion of vacuolatedDinophysiscells (72%) observed one week later suggests that the bloom was triggered by heterotrophic feeding on a co-occurring peak of Mesodiniumcoupled with advection of Dinophysiscells into the ría. Elevated frequencies of cells with starch and vacuoles were closely associated with the presence ofM.cfrubrum during the entire bloom season. However, peaks in the frequency of vacuolated cells were only recorded on a few occasions, suggesting that D. acuminatais prey-limited most of the time but does not require a constant supply of prey for long term survival. Infection of D. acuminataby the parasite dinoflagellateAmoebophryasp., a potential loss factor in the population dynamics of dinoflagellate populations, was observed (1–17% prevalence) immediately prior to the decline of the bloom. A conceptual model is presented of the mechanisms by whichD. acuminata blooms develop in a ría influenced by upwelling which utilizes a combination of physics (upwellingpromoted shoreward transport ofDinophysisinoculum) and the match–mismatch of predator–prey (DinophysisandMesodinium) populations.Versión del editor