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

Abstract

The distribution and physiological condition of the DSP-toxin producer Dinophysis acuminata, its relation with accompanying microplankton populations and coupling with upwelling events are described based on weekly sampling at a fixed station in Ría de Pontevedra, Galician Rías Baixas, NW Spain between March and December 2007. D. acuminata was detected from 18 June to 01 October. The appearance of D. acuminata in the Ría coincided with an upwelling-relaxation event and a short-lived maximum (up to 27000cellsL−1) of its potential prey, the phototrophic ciliate Mesodinium cf rubrum. An increase in the proportion of vacuolated Dinophysis cells (72%) observed one week later suggests that the bloom was triggered by heterotrophic feeding on a co-occurring peak of Mesodinium coupled with advection of Dinophysis cells into the ría. Elevated frequencies of cells with starch and vacuoles were closely associated with the presence of M. cf rubrum during the entire bloom season. However, peaks in the frequency of vacuolated cells were only recorded on a few occasions, suggesting that D. acuminata is prey-limited most of the time but does not require a constant supply of prey for long term survival. Infection of D. acuminata by the parasite dinoflagellate Amoebophrya sp., 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 which D. acuminata blooms develop in a ría influenced by upwelling which utilizes a combination of physics (upwelling-promoted shoreward transport of Dinophysis inoculum) and the match–mismatch of predator–prey (Dinophysis and Mesodinium) populations.