EFFECTS OF THE 1997-98 EL NIÑO EVENT ON SUBTIDAL BENTHIC POLYCHAETES FROM QUINTERO BAY, CENTRAL CHILE
Cañete-Aguilera, J. I.; Leighton, G. L. & Soto, E.
Instituto de Oceanología, Universidad de Valparaíso, Casilla 13-D, Viña del Mar, Chile
To evaluate the effects of the 1997-98 El Niño event on the shallow, subtidal polychaete communities of the central Chilean coast, data obtained in six monitoring cruises carried out between March, 1995 and August, 1997 (non Niño periods) were compared with data obtained in two other cruises undertaken in November 1997 and March 1998 in Quintero Bay (32o S, 71o 30' W; 6 to 13 m depth; four oceanographic stations). Abundance, species composition, and diversity recorded under both oceanographical regimes were analyzed. Total abundance ranged from 100 to 1000 indiv. m-¾, richness of species from 4 to 12 species per cruise, and values of the Shannon-Wiener diversity index varied from 0.6 to 1.3. Only three species (Nepthys impressa, Hemipodus simplex and Goniada uncinigera) were present in seven or all eight monitoring samples, and high numbers of rare species were recorded. The abundance of N. impressa, the principal species used as a bioindicator, ranged from 180 to 670 individuals per cruise. Under the El Niño oceanographical regime the abundance, species richness and diversity of polychaetes decreased by one or two orders of magnitude. The rare species collected in normal conditions were missing and only four species remained (the species listed above plus Dispio uncinata). The normal abundance of N. impressa decreased by one order of magnitude. The species present under El Niño conditions have geographical distributions extended to Peruvian coast, mainly N. impressa, but the abundance was not favoured by this increment of sea water temperature. In conclusion, this El Niño event had negative effects on the shallow, subtidal, benthic polychaetes from this Chilean embayment.