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vol.30 número1  suppl.SympInfluence of the El Niño - La Niña cycle on satellite-derived primary production in the California CurrentEl Niño 1997-98 by Means of Planktonic Foraminifera off Coquimbo, Chile índice de autoresíndice de materiabúsqueda de artículos
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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002 

Community Structure of Euphausiids
in the Southern Part of the California
Current during October 1997 (El Niño)
and October 1999 (La Niña)

Lorena Linacre Rojas, Bertha Lavaniegos Espejo

Centro de Investigación Científica y de Educación
Superior de Ensenada (CICESE).
Apdo. Postal 2832, Ensenada, B.C., México,

The beginning of El Niño 1997-1998 was marked by a warming of the surface water of the Central Tropical Pacific in March 1997. The event continued developing through April-May and reached its peak strength by June the same year. Central Pacific SST increased by 2-3°C above normal, and up to 4°C over the Eastern Pacific. During 1999-2000, following El Niño, stronger than usual trade winds typical of La Niña conditions developed. This favoured stronger upwelling and colder than normal waters along the coast of the North Eastern Pacific.

The California Current System (CCS) is known to be highly vulnerable to El Niño events. For the 1997-1998 El Niño, the first noticeable changes along the CCS were reported in July 1997, when the coastal poleward current expanded offshore transporting warmer and saltier water in the upper 100m. Also, changes in the circulation patterns were observed, particularly an offshore displacement of the core of the California Current and an increase in sea surface dynamic heights. Beginning in 1999, these conditions reverted, probably as a result of local atmospheric forcings.

Marine ecosystems of the Eastern Pacific are strongly affected by ENSO events. The response of the planktonic community is variable and depends on taxa. Changes may be noticed in biomass, abundance and distribution patterns as well as recruitment rates of some planktonic larvaL phases. Euphausiids, as other planktonic invertebrates, are subject to climatic changes. These may be cyclic as seasonal variability or longer temporal scales like those observed during an El Niño.

In this work, community structure of euphausiids is described between Punta Baja (30°N) and Punta Abreojos (26.7°N), Baja California, during El Niño (October 1997) and La Niña (October 1999) events. Zooplankton samples were collected during IMECOCAL (Investigaciones Mexicanas de la Corriente de California) cruises, a program that investigates the biophysical coupling along the CCS ecosystem off Baja California, from 1997 to the present. The goal of this study is to analyze the effects induced by warm (El Niño) and cold (La Niña) events on the abundance, composition, distribution and population structure of euphausiid species in the area. For this purpose, adults, juveniles, and larval stages (furcilias and calyptopes) of euphausiids of both periods were quantified and identified. A total of 24 species (7 genera) were found. Total Euphausiids abundance during the warm event (October 1997) was 16% higher than during the cold period of October, due mainly to a higher contribution of larvae during El Niño. Relative to total euphausiid abundance from each period, percentages of postlarval and larval stages in October 1997 were 39 and 61%, respectively. In October 1999 these values were 54 and 46%, respectively. The observed differences in life stages may indicate more intense reproductive activity during a warm period, or a better larval survival strategy compared to the cold period. The most abundant species during El Niño were Nyctiphanes simplex (84%), followed by Euphausia eximia (2%) and Stylocheiron affine (2%). During La Niña event, Nyctiphanes simplex (67%) continued to be the most abundant specie, and Nematoscelis difficilis (20%) increased in abundance significantly, followed by Euphausia gibboides (3%) and Thysanoessa gregaria (3%), species typically asociated with the California Current. Other species showed low abundance, but their presence in the area could be due to particular oceanographic conditions in both periods. Such is the case of Euphausia pacifica which was present during the cold period in October 1999, including southern stations. This species has an affinity to cold waters and is usually found in the northern part of the California Current. In contrast, in October 1997 species with tropical and equatorial affinity, such as Euphausia diomedeae, E. distinguenda, E. lamelligera, E. tenera and Nematoscelis gracilis, were recorded, due to the warming of waters during El Niño 1997-98, associated with a northward flow of subtropical waters introducing these species to the area.

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