The temporal and spatial distributions of zooplankton biomass and larval fish recorded during 27 months (December
1995–December 1998) off the Pacific coast of central México are analyzed. A total of 316 samples were obtained by surface
(from 40–68 to 0 m) oblique hauls at 12 sampling sites using a Bongo net. Two well-defined periods were observed: a
pre-ENSO period (December 1995–march 1997) and an ENSO event (July 1997–September 1998) characterized by
impoverishment of the pelagic habitat. The highest biomass concentrations occurred at coastal stations during the
pre-ENSO period. During the El Nin˜o period no spatial patterns were found in coastal waters. The months with highest
biomass were those in which the lowest sea surface temperature (SST) occurred (January–May), and this pattern was also
observed during the ENSO period. A typical, although attenuated, seasonal environmental pattern with enhanced phytoplankton
(diatoms and dinoflagellates) was prevalent during the El Nin˜o event in nearshore waters. During the El Niño
period the phytoplankton was mainly small diatoms (microphytoplankton), while dinoflagellates were practically absent.
The most parsimonious generalized linear models explaining spatial and temporal distribution of larval fish species
included the ENSO index (MEI), upwelling index (UI) and distance to the coast. The environmental variability defined
on an interannual time-scale by the ENSO event and the seasonal hydroclimatic pattern defined by the UI (intra-annualscale)
controlled the ecosystem productivity patterns. The small-scale distribution patterns (defined by a cross-shore gradient)
of plankton were related to the hydroclimatic seasonality and modulated by interannual anomaliesUniversidad de Guadalajara, Méxic
