Dinoflagellatae of Peruvian sea as indicators of water masses during 1982 to 1985

Abstract

The normal primary production along the Peruvian coast, in terms of phytoplankton composition is usually high with a low diversity index. However, during El Niño event warm water masses approach the coast from the Northwest (low salinity) and from West (high salinity); the production decreases and the diversity index increases threefold. This is due to a change of the predominant phytoplankton species composition from diatoms to dinoflagellates. The main goal of this study was to find out which species of dinoflagellates could be considered as good indicators of these different water masses. Then, by following the movements of these species we could describe the beginning, growth and end of El Niño along the Peruvian coast. Plankton samples were collected with a standard phytoplankton net from 1982 to 1985, during which two different periods: "El Niño" phenomenon (1982-1983) and a normal period (1984-1985) were observed. Qualitative and quantitative analysis were made identifying more than 180 species, and their distribution in relation to temperature and salinity data. Group of species including Ceratium breve, Ornithocercus seleinii, O. thumii and Amphisolenia thrinax were found in waters with high temperatures and low salinity (Surface Equatorial Water masses). Ceratium belone, C. bigelowii, C. praelongum and Goniaulax pacifica, were associated to the high temperatures and high salinity of Surface Subtropical Water masses; other species such as Ceratocorys horrida, C. armata, Ornithocercus quadratus, Ceratim gibberum and Amphisolenia bidentata are more associated with high temperatures independent of the salinity influence. During El Niño the only species of the typical cold coastal waters found was Protoperidinium obtusum. Most of these species have been recorded in previous studies as good indicators of water masses.