On-line version ISSN 0717-7178
Investig. mar. vol.30 no.1 suppl.Symp Valparaíso Aug. 2002
Effects of El Niño 1997-1998 on
Copepod Community Structure at San
José Coastal Station (Peru)
Katia Aronés Flores, Patricia Ayón Dejo
Copepoda is the most abundant and frequent group of the zooplankton communities and shows high sensitivity to environmental changes like "El Niño" events. San José (06° 50 S) is a coastal observation point located in the northern part of Perú. It is permanently influenced by cold coastal waters (CCW) of the Peruvian sea, and presents upwellings throughout the year. These characteristics make San José an ideal place to recognize environmental changes like "El Niño" events. In this paper, we have determined changes in structure and richness of copepod communities during the "El Niño" event of 1997-1998.
1996 was a typical year with cold environmental conditions when community parameters like diversity, specific richness and evenness values were similar to the averages found between 1996 and 2001. Under the influence of the "El Niño" event in 1997-1998 this community showed the highest values of diversity, specific richness and evenness, due to the incursion of northern warm waters, which carried different species to the local ones.
Fig. 1. Zooplankton Sampling Stations - ECF San José 1996-2001.
A Principal Components Analysis (PCA) was performed to show the relationships among species at sampling stations and water mass characteristics. It showed a high correlation between the C. brachiatus and C. furcatus populations and CCW and Surface Equatorial Waters (SEW).
During the study period, the most abundant and frequent species were Paracalanus parvus, Calanus australis and Acartia tonsa. P. parvus was dominant in 1996, 1997 and 1999, while C. australis was associated with oceanic waters in 1998; and finally A. tonsa was dominant from 2000 to 2001.
Fig. 2. Alternation of two copepod species between 1996 and 2001 (ECF San José).
C. australis is two times the length of the other species and has long appendages which allow it to catch more big particles, so we found that years characterized by high concentrations of large cells were dominated by this species, while P. parvus and A. tonsa were dominant species in years when the sea contained high concentrations of small cells. That means that normal and cold periods (where upwelling occurs along the coast) allow those species to dominate the system, specially Acartia tonsa.
Centropages barchiatus is a species of the Peruvian coast characterized as an indicator of CCW, and is also frequently found in a typical community structure under normal and cold water conditions. However, during the El Niño event from August 1997 to November 1998, it wasn't found. This was previously reported by Ayón et. al (1999), who described a subsequent disappearance of this species in samples taken from north to south as far as Pisco (14°00S). It has been observed that adult stages die but leave eggs in a diapause stage that revert only in normal conditions.
On the other hand, C. furcatus was integrated into the community composition since April 1997. The density of this specie increased throughout the year until June 1998, and afterwards decreased, disappearing late in 1998; it was not found between 1999 and 2001. A high negative correlation (a = 0.01) between C. brachiatus and C. furcatus was determined.