Community structure of the euphausiid population along the west coast of Baja California, Mexico, during the weak ENSO 1986-1987

Abstract

Changes in the community structure and distribution patterns of 20 species of euphausiids collected during 6 oceanographic cruises along the southwest coast of Baja California during El Nifio Southern Oscillation (ENSO) 1986-1987 were compared with the data from 5 cruises made Turing ENSO 1982-1983. The possible existence of different influences of environmental conditions on the dlstnbution, abundance, and community structure of euphausl~dsd uring 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 SST anomaly (1°C) was observed during the second half of 1987, reaching latitude 26" N. The composition of species during this study showed a high proportion of tropical and ecuatorial endemic Eastern Tropical Pacific (ETP) species, north and south margin ETP proliferator species, and warm water cosmopolitan species. There was a scarcity of California Current terminus species. Euphausia pacifica Hansen and Thysanoessa gregaria G. 0. Sars, 2 temperate species, were considered to have moved from their reproductive areas. Nyctiphanes simplex Hansen dominates the euphausiid fauna of the west coast of Baja California and was most plentiful near the shore. Its reproductive activity was mainly in upwelling regions. Seasonal and latitudinal variability of the intensity of the upwelling along the peninsula could have a strong influence on the range of distribution of its highest abundance centers. The southern region was dominated by tropical and equatorial endemic ETPadapted species showing reproductive activity. Compared to ENSO 1982-1983, the influence of ENSO 1986-1987 on the community of euphausiids in the southern part of Baja California was small.