Importancia ecológica del fitoplancton durante El Niño 1991-1993, en el Pacífico Ecuatorial (Ecuador)

Abstract

El objetivo del estudio fue determinar su importancia ecológica y diversidad de los principales grupos del fitoplancton durante El Niño 1991-1992, en tres cruceros realizados en la época cálida-húmeda del ecosistema del Pacífico Ecuatorial (1991, 1992 y 1993).

Thirty one surface and twenty four sub-surface (50 m) oceanographic stations were analyzed during three cruises: December 1991, march 1992 and march 1993. During this period a strong "El Niño" 1991-92 event appeared. The physical conditions during the development of "El Niño 91-92" event did not present a defined pattern during the three cruises, showing particular characteristics for each studied region of the Equatorial East Pacific Ocean. Evidence that the phytoplankton decreased drastically in december 1991 was found approximately three months before the high temperatures of march 1992. However, the biological productivity in march 1992 increased, probably due to the development of an intense sub-surface upwelling. Later in march 1993, the anomalous "El Niño" conditions prevailed, with the higher chlorophyll layer deepened to approximately 40m, specially, in the south west of the studied area. The main species with high cell density in the three cruises were B. splendor-maris, P. sol, G. polyedricum, C. tripos, R. alata, R. hebetata. These species showed variability in their distribution, presenting nucleus of associated Diatoms and Dinoflagellates. These environment conditions allowed us to establish the existence of inter-specific components between generalist species (diatoms) and specialist species (dinoflagellates); both groups were eurithermic species during "El Niño 1991-93".