Oscillations of macrobenthos in shallow waters of the Peruvian central coast induced by EI Niño 1982-83

Macrozoobenthos was sampled at 15 m (January 1982–October 1984) and 34 m depth (September 1981–September 1984) in the Bay of Ancón, north of Lima. Fluctuations in density, biomass, species composition and diversity of the fauna as well as oscillations in the density of several dominant species were studied in relation to temperature, salinity and dissolved oxygen. El Niño (EN) 1982–83 induced marked positive effects at both depths. Some of these changes prevailed in 1984 due to the increase of oxygen close to the seafloor and the persistence of higher O2 values during and after the phenomenon. The number of species at 15 m, which before EN fluctuated between 3 and 17, increased to \u3e26 (max. 45) during EN and in the months following the event. Biomass, before EN always \u3c1 g, reached 18.4 g AFDW per m2 in December 1982. Density, normally \u3c4000 per m2, increased to 1724, and diversity nearly doubled and remained high until September 1984. The number of species at 34 m (≥5 before EN) fluctuated between 15 and 24 from December 1982 to February 1983 and returned to ≥5 by June 1984. Biomass reached 6.9 g AFDW per m2 in December 1982. Density, normally \u3c425 per m2, increased to 13550, and diversity at this depth nearly tripled in February 1983