COMMUNITY STRUCTURE OF THE EUPHAUSIID POPULATIONS ALONG THE WEST-COAST OF BAJA-CALIFORNIA, MEXICO, DURING THE WEAK ENSO 1986-1987

Changes in the community structure and distribution patterns of 20 spe cies of euphausiids collected during 6 oceanographic cruises along the southwest coast of Baja California during El Nino Southern Oscillatio n (ENSO) 1986-1987 were compared with the data from 5 cruises made dur ing ENSO 1982-1983. The possible existence of different influences of environmental conditions on the distribution, abundance, and community structure of euphausiids during the 2 periods was assessed. Although a time series of surface temperature (SST) from 3 latitudinal regions along the west coast of Baja California during 1980 and 1990 showed no evidence of a long-term warming in 1986 and early 1987, a positive SS T anomaly (1 degrees C) was observed during the second half of 1987, r eaching latitude 26 degrees N. The composition of species during this study showed a high proportion of tropical and equatorial endemic East ern Tropical Pacific (ETP) species, north and south margin ETP prolife rator species, and warm water cosmopolitan species. There was a scarci ty of California Current terminus species. Euphausia pacifica Hansen a nd Thysanoessa gregaria G. O. Sars, 2 temperate species, were consider ed to have moved from their reproductive areas. Nyctiphanes simplex Ha nsen dominates the euphausiid fauna of the west coast of Baja Californ ia and was most plentiful near the shore. Its reproductive activity wa s mainly in upwelling regions. Seasonal and latitudinal variability of the intensity of the upwelling along the peninsula could have a stron g influence on the range of distribution of its highest abundance cent ers. The southern region was dominated by tropical and equatorial ende mic ETP-adapted species showing reproductive activity. Compared to ENS O 1982-1983, the influence of ENSO 1986-1987 on the community of eupha usiids in the southern part of Baja California was small.