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Sakina-Dorothée Ayata

Laboratoire d'Océanographie de Villefranche (UMR 7093)
La Darse - BP 28
06234 Villefranche-Sur-Mer Cedex

Tel : +33 (0)4 93 76 38 63
Associate Professor
Biological Oceanography

Present lab: LOV / UPMC
Former labs: INRIA / LOCEAN-IPSL, Station Biologique de Roscoff / UPMC.

Journal articles

S D Ayata, M Lévy, O Aumont, A Sciandra, J Sainte-Marie, A Tagliabue, O Bernard (2013)  Phytoplankton growth formulation in marine ecosystem models : Should we take into account photo-acclimation and variable stoichiometry in oligotrophic areas?   Journal of Marine Systems  
Abstract: Abstract The aim of this study is to evaluate the consequences of accounting for variable Chl:C (chlorophyll:carbon) and C:N (carbon:nitrogen) ratios in the formulation of phytoplankton growth in biogeochemical models. We compare the qualitative behavior of a suite of phytoplankton growth formulations with increasing complexity: 1) a Redfield formulation (constant C:N ratio) without photo-acclimation (constant Chl:C ratio), 2) a Redfield formulation with diagnostic chlorophyll (variable and empirical Chl:C ratio), 3) a quota formulation (variable C:N ratio) with diagnostic chlorophyll, and 4) a quota formulation with prognostic chlorophyll (dynamic variable). These phytoplankton growth formulations are embedded in a simple marine ecosystem model in a 1D framework at the Bermuda Atlantic Time-series (BATS) station. The model parameters are tuned using a stochastic assimilation method (micro-genetic algorithm) and skill assessment techniques are used to compare results. The lowest misfits with observations are obtained when photo-acclimation is taken into account (variable Chl:C ratio) and with non-Redfield stoichiometry (variable C:N ratio), both under spring and summer conditions. This indicates that the most flexible models (i.e., with variable ratios) are necessary to reproduce observations. As seen previously, photo-acclimation is essential in reproducing the observed deep chlorophyll maximum and subsurface production present during summer. Although Redfield and quota formulations of C:N ratios can equally reproduce chlorophyll data the higher primary production that arises from the quota model is in better agreement with observations. Under the oligotrophic conditions that typify the BATS site no clear difference was detected between quota formulations with diagnostic or prognostic chlorophyll.
Sakina-Dorothee Ayata, Robin Stolba, Thierry Comtet, Eric Thiebaut (2011)  Meroplankton distribution and its relationship to coastal mesoscale hydrological structure in the northern Bay of Biscay (NE Atlantic)   JOURNAL OF PLANKTON RESEARCH 33: 8. 1193-1211 AUG 2011  
Abstract: The relationship between meroplankton distribution and spatio-temporal variability of coastal mesoscale hydrological structure was investigated in the northern Bay of Biscay, North-East Atlantic. For the three coastal polychaetes studied, i.e. Pectinaria koreni, Owenia fusiformis and Sabellaria alveolata, the highest larval abundances were sampled in low-salinity, low-density and high-temperature river plume waters. For two species (P. koreni and O. fusiformis), maximal abundances were observed in the surface and thermocline layers due to ontogenic migrations. Variance partitioning based on multiple regression and redundancy analyses was used to assess the relative roles played by the hydrological environment alone, the geographical space alone and their interactions, i.e. the spatial structure of the hydrological environment. These analyses demonstrate the key role played by the hydrological spatial structure in the distribution of larval abundances. The hydrological environment alone was insignificant, whereas geographical space alone explained a significant part of the variability in meroplankton distribution, probably in conjunction with ecological processes. For species whose benthic populations are spatially structured, the distribution and the size of adult populations and the timing of spawning events can significantly affect larval distribution and dispersal.
Notes: Times Cited: 0
Francois Rigal, Frederique Viard, Sakina-Dorothee Ayata, Thierry Comtet (2010)  Does larval supply explain the low proliferation of the invasive gastropod Crepidula fornicata in a tidal estuary?   BIOLOGICAL INVASIONS 12: 9. 3171-3186 SEP 2010  
Abstract: Human-mediated transport and aquaculture have promoted the establishment of non-indigenous species in many estuaries around the world over the last century. This phenomenon has been demonstrated as a major cause of biodiversity alterations, which has prompted scientists to provide explanations for the success or failure of biological invasions. Crepidula fornicata is a gastropod native from the East coast of North America which has successfully invaded many European bays and estuaries since the 19th century, with some noticeable exceptions. Its spread over Europe has been explained by a combination of human-mediated transport and natural dispersal through its long-lived planktonic larva. We here investigated whether larval supply may explain the failure in the proliferation of this species within a particular bay, the Bay of Morlaix (France). Patterns of larval distribution and larval size structure were analysed over ten sites sampled three times (20 July, 4 August and 21 August 2006), regarding characteristics of the adult population and environmental features. Our results evidenced a strong spatial structure in both larval abundance and size at the bay scale, even if larval abundances were low. In this scheme, the location of spawning adults played a critical role, with high numbers of early larvae above the main spawning location. The larval size structure further showed that settlement-stage larvae were rare, which suggested that released larvae might have been exported out of the bay. The use of an analytical model aimed to study the effect of tidal currents on the potential for larval exportation confirmed that larval retention within the bay might be low. The limitation in larval supply resulting from the interactions between spawning location and local hydrodynamics may thus impede the proliferation of this species which is well established for more than 50 years. This study provided an example of factors which may explain the failure of the transition between two major steps of biological invasions, i.e. sustainable establishment and proliferation.
Notes: Times Cited: 1
Sakina-Dorothee Ayata, Pascal Lazure, Eric Thiebaut (2010)  How does the connectivity between populations mediate range limits of marine invertebrates? : A case study of larval dispersal between the Bay of Biscay and the English Channel (North-East Atlantic)   PROGRESS IN OCEANOGRAPHY 87: 1-4. 18-36 OCT  
Abstract: For many marine species, larval dispersal plays a crucial role in population persistence, re-colonization of disturbed areas, and distribution of species range limits through the control of population connectivity. Along the French Atlantic coast (NE Atlantic), a biogeographical transition zone has been reported between temperate and cold-temperate marine faunal assemblages. Hydrodynamics in this area are highly complex and variable including numerous mesoscale features (e.g. river plumes, fronts, upwellings, low salinity lenses), which could constrain larval transport and connectivity. In this context, the aim of this study was to assess how hydrodynamic conditions and biological traits influence larval transport and contribute to population connectivity along the biogeographical transition zone between the Bay of Biscay and the English Channel. A coupled bio-physical individual-based model was used at a regional scale to track larval trajectories under realistic hydroclimatic conditions (tides, river run-offs, and meteorological conditions) and for some common life-history traits. Larval particles were released monthly from February to August for the years 2001 to 2005, from 16 spawning populations corresponding to the main bays and estuaries of the study area. Two planktonic larval durations (2 vs. 4 weeks) and three vertical distributions (no swimming behaviour, diel vertical migration, and ontogenic vertical migration) were considered. Dispersal kernels were described by 17 parameters and analysed in a multivariate approach to calculate connectivity matrices and indices. The main factors responsible for the variability of the dispersal kernels were the spawning month in relation to the seasonal variations in river run-offs and wind conditions, the planktonic larval duration, the spawning population location, and the larval behaviour. No significant inter-annual variability was observed. Self-retention rates were high and larval exchanges occurred mainly within the main hydrodynamical areas: the western English Channel, the Southern Brittany, and the Central Bay of Biscay. Connectivity between the English Channel and the Bay of Biscay populations was low and occurred only under particular hydroclimatic conditions (i.e. high river run-off and strong SW winds) and for some biological traits (i.e. long planktonic larval duration). (C) 2010 Elsevier Ltd. All rights reserved.
Notes: Times Cited: 4
Christophe Lett, Sakina-Dorothee Ayata, Martin Huret, Jean-Olivier Irisson (2010)  Biophysical modelling to investigate the effects of climate change on marine population dispersal and connectivity   PROGRESS IN OCEANOGRAPHY 87: 1-4. 106-113 OCT  
Abstract: Climate may act on the dispersal and connectivity of marine populations through changes in the oceanic circulation and temperature, and by modifying species' prey and predator distributions. As dispersal and connectivity remain difficult to assess in situ, a first step in studying the effects of climate change can be achieved using biophysical models. To date, only a few biophysical models have been used for this purpose. Here we review these studies and also include results from other recent modelling efforts. We show that increased sea temperature, a major change expected under climate warming, may impact dispersal and connectivity patterns via changes in reproductive phenology (e.g., shift in the spawning season), transport (e.g., reduced pelagic larval duration under faster development rates), mortality (e.g., changes in the exposure to lethal temperatures), and behaviour (e.g.. increased larval swimming speed). Projected changes in circulation are also shown to have large effects on the simulated dispersal and connectivity patterns. Although these biophysical modelling studies are useful preliminary approaches to project the potential effects of climate change, we highlight their current limitations and discuss the way forward, in particular the need for adequate coupled hydrodynamic-biogeochemical simulations using atmospheric forcing from realistic climate change scenarios. (C) 2010 Elsevier Ltd. All rights reserved.
Notes: Times Cited: 5
Sakina-Dorothee Ayata, Celine Ellien, Franck Dumas, Stanislas Dubois, Eric Thiebaut (2009)  Modelling larval dispersal and settlement of the reef-building polychaete Sabellaria alveolata : Role of hydroclimatic processes on the sustainability of biogenic reefs   CONTINENTAL SHELF RESEARCH 29: 13. 1605-1623 JUN 30 2009  
Abstract: The honeycomb worm Sabellaria alveolata forms biogenic reefs which constitute diversity hotspots on tidal flats. The largest known reefs in Europe, located in the Bay of Mont-Saint-Michel (English Channel), are suffering increasing anthropogenic disturbances which raise the question of their sustainability. As the ability to recover depends partly on the recolonization of damaged reefs by larval supply, evaluating larval dispersal and the connectivity between distant reefs is a major challenge for their conservation. In the present study, we used a 3D biophysical model to simulate larval dispersal under realistic hydroclimatic conditions and estimate larval retention and exchanges among the two reefs of different sizes within the bay. The model takes into account fine-scale hydrodynamic circulation (800 x 800 m(2)), advection-diffusion larval transport, and gregarious settlement behaviour. According to the field data, larval dispersal was simulated for a minimal planktonic larval duration ranging from 4 to 8 weeks and the larval mortality was set to 0.09 d(-1). The results highlighted the role played by a coastal eddy on larval retention within the bay, as suggested by previous in situ observations. Very different dispersal patterns were revealed depending on the spawning reef location, although the two reefs were located only 15 km apart. The settlement success of the larvae released from the smallest reef was mainly related to tidal conditions at spawning, with the highest settlement success for releases at neap tide. The settlement success of the larvae from the biggest reef was more dependent on meteorological conditions: favourable Wand SW winds may promote a ten-fold increase in settlement success. Strong year-to-year variability was observed in settlers' numbers, with favourable environmental windows not always coinciding with the main reproductive periods of Sabellaria. Settlement kinetics indicated that the ability to delay metamorphosis could significantly improve the settlement success. Although bidirectional exchanges occurred between the two reefs, the highest settlers' numbers originated from the biggest reef because of its stronger reproductive output. Because of the recent decline of this reef due to increasing anthropogenic disturbances larval supply in the bay may not be sufficient enough to ensure the sustainability of the remarkable habitat formed by Sabellaria alveolata reefs. (c) 2009 Elsevier Ltd. All rights reserved.
Notes: Times Cited: 7

PhD theses

Ayata Sakina-Dorothée (2010)  Importance relative des facteurs hydroclimatiques et des traits d'histoire de vie sur la dispersion larvaire et la connectivité à différentes échelles spatiales (Manche, Golfe Gascogne).   Université Pierre & Marie Curie. UPMC - Paris 6. Station Biologique de Roscoff. Place Georges Teissier. 29680 Roscoff, France.:  
Abstract: By ensuring the dispersal, the larval phase plays a fundamental role in the population dynamics of benthic invertebrates with a complex life cycle and determines the connectivity within marine metapopulations. Hence, the connectivity influences directly the dynamics of metapopulations and the persistence of local populations, the expansion abilities of species in response to changes in environmental conditions or biogeographic range limits. In this context, the aim of the present work was to better understand the relative roles played by hydrodynamics and hydroclimatic processes and life history traits of coastal invertebrates on the larval dispersal and the connectivity in the Bay of Biscay and in the western English Channel. To answer this question, a coupled approach was used, joining in situ observation and bio-physical modelling at two spatial scales, a regional one and a local one. In the northern Bay of Biscay, the description of larval distribution of three coastal species of polychaetes (Pectinaria koreni, Owenia fusiformis, and Sabellaria alveolata) highlighted the major role of the spatial organization of the mesoscale hydrological structures (i.e., river plumes) in the the variability of larval abundance distributions. At the regional scale of the Bay of Biscay and the western English Channel, the Lagrangian simulation of the larval dispersal under realistic hydroclimatic forcing underlined the importance of the seasonal variability of the hydroclimatic conditions and the life history traits (spawning month, planktonic larval duration, larval swimming behaviour) in the larval transport and connectivity between populations. These results suggested possible larval exchanges from the Bay of Biscay to the western English Channel, i.e. through a biogeographic transition zone. They allowed to test several hypothesis about the potential consequences of climate change on the dispersal and connectivity of marine populations, i.e. through an earlier spawning period and a shortened planktonic larval duration. At the local scale of the Gulf of Saint-Malo, western English Channel, an Eulerian dispersal model permitted to estimate the connectivity between the biogenic reefs built by Sabellaria alveolata, a species with a high patrimonial value. This model allowed to determine the relative influences of the intra- and inter-annual variability of the hydroclimatic conditions on connectivity, in a context of management and conservation of natural heritage.
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