Ricardo Palomares-García

Estructura de la comunidad de copépodos en Bahía Magdalena, México, durante El Niño 1997-1998

Seasonal changes in copepods taxocoenosis associated to environmental changes caused by El Nino 1997/98 were evaluated during the four most intensive months of the event. Sixty six copepod species were identified. In May, before the arrival of warm waters to the area, the taxocoenosis structure was characterized by a high dominance, low diversity and the predominance of two species of temperated affinity: Calanus pacificus and Labidocera trispinosa. During the warm period (August and November), the dominant species were of tropical affinity, such as Acartia clausi and A. lilljeborgii. In August, diversity increased in the stations influenced by oceanic waters whereas in November, diversity increased in the entire bay; in January, the dominance was relative low and the most abundant tropical species was Paracalanus aculeatus, and a general increase of the diversity was observed in the entire bay. Two environmental zones in the bay were identified: one characterized by internal waters of the bay, with resident species and with those species frequently entering the bay by tidal currents, and another zone characterized by the influence of outside oceanic waters, with the dominance of oceanic or neritic species. In this last area, it is more clearly reflected the warm water arrival and its associated fauna. The most remarkable changes in the copepods community were coincident with the occurrence of positive temperature anomalies. Changes included a 75% increase of species of tropical affinity and the presence of Pontella fera, which had not been previously recorded in the area, and the replacement of the temperate species P. parvus, by P. aculeatus, a species of tropical affinity.

Variabilidad de la abundancia de zooplancton en Bahía Magdalena Baja California Sur, México (1997-2001)

RESUMEN. Se analizaron muestras de zooplancton de 16 campanas oceanograficas, efectuadas en Bahia Magdalena, Baja California Sur, Mexico, entre agosto de 1997 y marzo de 2001. Se identifico un total de 26 grupos taxonomicos, de los cuales los mas abundantes y frecuentes fueron copepodos y quetognatos; en 2000-2001 se observo una tendencia a disminuir entre 10 y 20 el numero de grupos de zooplancton. La biomasa zooplanctonica y abundancia de copepodos disminuyeron en el periodo de estudio, en contraste con los quetognatos que tuvieron un ligero aumento. Las fluctuaciones de abundancia de zooplancton no estuvieron relacionadas con la concentracion de clorofila- a , a diferencia de los maximos de abundancia de zooplancton, que estuvieron asociados a los cambios de la temperatura superficial del mar. El ciclo estacional de la abundancia del zooplancton en Bahia Magdalena, indico que en invierno el promedio fue mayor de 65.000 ind 100 m -3 , valor que aumento en primavera a mas de 99.000 ind 100 m

Influence of hydrographic conditions on larval fish assemblage structure in the northern Gulf of California

This paper analyzes the seasonal variability on larval fish assemblage structure and the relationships to hydrographic conditions during 4 seasonal surveys i...