Hydrographic variability in Bahia de La Paz, B. C. S, Mexico, during the 1997-1998 El Niño

Abstract

Bahía de La Paz, the largest coastal bay in the Gulf of California, is characterized by high diversity of fish species, mainly during summer and autumn. Distributions and abundances of fish larvae in the bay were analyzed and compared with zooplankton, CTD, current and satellite data obtained in July 1997 and August 1998. Larval abundance (>4000 larvae per 100 m3) and number of species (>90 species) were high during both cruises. The Bray-Curtis dissimilarity index was used to define three station groups. The "Coastal" group, with the highest abundance and number of species, was located mainly in the shallow basin of the bay (<30 m depth). Larval Gerreidae (e.g. Eucinostomus gracilis, E. dowii, and Diapterus peruvianus) and Pomacentridae (Abudefduf troschelii and Stegastes rectifraenum) were the most abundant taxa in this station group, but larval Mullidae (Mulloidichthys dentatus) also were abundant in August 1998. This station group was associated with the highest zooplankton biomass and lowest sea-surface temperature as a result of mixing by the winds and tidal currents that affect this shallow zone. The "Central-A" station group, located in the central bay, and the "Central B" group situated nearby, had low larval abundance and number of species. These station groups coincided with the lowest zooplankton biomass and highest sea-surface temperature in both summers, and with the location of a cold gyre at 50 m depth in July 1997. These conditions are influenced by the water entering from the Gulf of California through the main mouth of the bay (>100 m), resulting in a wide central zone with low larval abundance during both summers.