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vol.30 número1  suppl.SympPredicting the Effects of El Niño on Seaweeds from Baja California, MexicoDiversity of the Sublittoral Macroinfauna in Bahía Iquique during and after the 1997-98 "El Niño" Event 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 

Effects of "El Niño" Events on the
Sublittoral Macroinfauna in
Bahía Iquique, Chile

Rodrigo Moreno M.1,
Roger Sepúlveda S.1,3,
Franklin Carrasco V.2, Raúl Soto M.4

1Depto. de Zoología, 2Depto. de Oceanografía, Fac. de
Ciencias Naturales y Oceanográficas, Univ. de
Concepción. Casilla 160-C, Correo 3, Concepción,
Chile. E-mail:
3Depto. Ecología Costera, Facultad de Ciencias, Univ.
Católica de la Ssma. Concepción
4Departamento de Ciencias del Mar, Univ. Arturo Prat.

The aim of the present study was to explore the seasonal changes experienced by community attributes of the benthic sublittoral macroinfauna of Bahía Iquique (20º 10' S, 70º 09' W) during and after the EN97/98 event with abiotic variables.

The results indicate that during EN97/98, high values of abundance and biomass for the invertebrates Polychaeta (49.83%, 8.1g), Mollusca (26.6%, 40.57g) and Crustacea (15.45%, 45.68g) were recorded. The species richness recorded was of 59 taxa, with a value of total alpha diversity of 4.171 and an evenness of 0.709, while the conformation of the functional groups was characterized by the dominance of carnivorous forms.

After EN97/98, variations in the proportions of relative abundance and biomass of Polychaeta (60.4%, 18.21g), Mollusca (33.17%, 50.25g) and Crustacea (2.84%, 1.33g) were recorded. The species richness recorded was inferior to the previous period with a total of 52 taxa. The total species diversity was of 3.519 and the evenness of 0.617, values that were associated with the high ecological dominances mediated by polychaetes. The conformation of functional groups was characterized by filter-feeder and deposit-feeder forms.

The polychaetes were most abundant, contributing 54.90% of the total fauna. In both periods analyzed, the contributions of the spionid Paraprionospio pinnata (69.38%) and the gastropod Nassarius gayi (27.77%) were the most important.

The hydrographic conditions observed during and after EN97/98 were characterized by the presence of seasonal variations in bottom temperature and dissolved oxygen content, with the highest temperatures (23º C) and concentrations of oxygen (5.5ml O2 L-1) recorded during EN97/98, associated with the intrusion of warm waters to the bay. After EN97/98 low values of bottom temperature (11.9ºC) and dissolved oxygen (0.9 ml O2 L-1) were recorded, associated with the reestablishment of the processes of coastal semi-anoxic upwelling characteristic of the spring period in the north of Chile.

The patterns observed agreed with those described by Arntz (1986) and Tarazona et al. (1988a, 1988b, 1996) in superficial areas in the south of Perú affected by the EN82/83 event and also with the fluctuations in the system of upwelling.

The community ordination reveals that the compositions of the major groups changed prominently at species level for each period analyzed, due mainly to the environmental changes recorded in the hydrographic conditions of the bay.Dissolved oxygen at the bottom was the only environmental variable that presented significant correlations with species richness and species diversity in both periods analyzed (rc7=0.687 and rc7=0.666; p=0.05). This suggests that the variations observed in the community structure of both periods was ruled by the seasonal changes in the availability of dissolved oxygen at the bottom, a consequence of the effects of EN97/98 on the area of Bahía Iquique.

The fauna composition of the bay during EN97/98 was characterized by the presence of high abundances of polychaetes, molluscs and crustaceans, a pattern that was also observed elsewhere in Perú and north and central Chile. After EN97/98 the same fauna composition of the previous period was observed, thus the major abundances corresponded to Polychaeta and Mollusca, while there was a lower contribution by the Crustacea group. This pattern is correlated with the low values of dissolved oxygen for this period of study, which were probably regulating the presence of this group in this bay.

The dominance of the polychaete Paraprionospio pinnata in this study is very important, acting as a structural component characteristic of the benthic communities influenced by the Humboldt Current in the Southeastern Pacific Ocean.

The benthic communities present in the areas of coastal upwellings in the north of Chile and Perú are subject to severe and permanent hypoxia, associated with aperiodic events of the warm phase of "El Niño" (Arntz et al., 1991; Díaz & Rosenberg, 1995). These conditions appear favourable to the benthic ecosystem due to the improvement of the bottom oxygen levels, which show changes in the diversity of the community, as well as in the abundance, biomass and species richness (Tarazona et al., 1988a, 1988b, 1996) - a similar pattern as was recorded in this study.

Arntz et al. (1991) and Gallardo et al. (1995) have stressed that the structure of benthic communities in Perú and the north of Chile show a pattern with low values of abundance, biomass and species diversity, influenced by the high ecological dominances to conform to a simple community organization, characteristic of the hypoxic ecosystems. The results of this study are in agreement with these statements when observing clearly that after the "El Niño" event that pattern is reestablished. The seasonal changes recorded in the benthic macrofauna of Bahía Iquique allow us to consider this type of oceanographic event as a natural, a modifying and a regulating agent of marine communities located in shallow embayments of northern Chile.

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