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

During July 2006 a cruise was carried out in the Northern Bay of Biscay (off Brittany France) to study meso and microscale patterns of phytoplankton distribution Moderate concentrations (10(2)-10(3) cells L-1) of Dinophysis acuminata were constrained to specific depths (upper layers above the pycnocline) at stations with lower surface salinity (34 5) and steep temperature gradients (18-13 5 C between 4 and 7 m depth) within the Loire and Vilaine river plumes On board incubations revealed a healthy D acuminata population at the biomass maxima with 89% of viable (FDA-treated) cells and moderate division rates (up to 010 d(-1)) Despite its good physiological condition the population of D acuminata declined rapidly to undetectable levels during the second leg of the cruise A 3D Lagrangian Particle-Tracking Model (3D LPTM) was used to simulate the transport of D acuminata cells in the Loire and Vilaine river plumes from 15 June to 30 July This 3D LPTM model was coupled to a MARS3D (Model for Applications at Regional Scale) model previously calibrated and validated for the region Model results suggest that physical processes alone could explain the dispersion of the D acuminata population within the area The application of a 3D LPTM model shows how individual based model approaches are valuable to identify Dinophysis spp transport pathways and reproduce retention/dispersion patterns observed in the field (C) 2010 Elsevier BV All rights reserved