Toxic red-tide in the Argentine Sea. Phytoplankton distribution and survival of the toxic dinoflagellate Gonyaulax excavata in a frontal area

Abstract

The association of the first bloom of the toxic dinoflagellate Gonyaulax excavata with the frontal system off Peninsula Valdés (Argentina), and the presence of resting cysts in sediments of the area gave way to the hypothesis of a second bloom during the subsequent spring. In this work we report on the results obtained after the study of the second bloom. The characteristics of the frontal system in relation to the development of the phenomenon are analyzed, and latitudinal differences are established. The presence of resting cysts in the plankton of the homogeneous side of the front indicates that the phenomenon is related to the transportation of these cysts from the sediments to the stratified side of the front, where stability and availability of nutrients favor a fast growth. Selection, imposed by turbulence, limits the growth of G. excavata at the homogeneous side where chain-forming diatoms develop. The presence of the red patch for a long time suggests a zooplankton-phytoplankton uncoupled interaction based on the zooplankton exclusion and its replacement by the phagotrophic dinoflagellate Polykrikos schwartzii . The highest predation pressure is located at the patch edges of the stratified zone.