Distribution of Nyctiphanes simplex larvae in relation to development stage and presence of fecund females is described for January-February, April, July and October 1966 in the area between Point Baja and Point Abreojos, off Baja California, Mexico. Recruitment was observed to be year round, but most intensive in fall and winter. Largest aggregations of fecund females ( > l 0 ind, m-2) occurred off Point Baja-Point Canoas in all months except July. Vizcaino Bay seems to be a feeding site in winter and a very important reproduction site in fall. Heating of waters offshore and the presence of a clockwise eddy inside Vizcaino Bay at the end of the most intensive months of upwelling constrained the distribution of females. Although fewer spawning females (carrying external eggs or spent) were present during winter, spring and summer, females in those seasons had greater body lengths (11.3, 12.4 and 11.6 mm on average respectively) than those during fall (10.1 mm on average). The largest spawning female (15.8 mm) was found in July off Point Eugenia. Proportions of particular furcilia forms in stages F, to F2 (distinguished by the degree of development of pleopods) were more similar along the north-south axis than onshore-offshore, following the generally along-shore onentation of isotherms. Dominance of short developn~ental pathways in F, and F2 stages (single instar in each stage) was most often observed near the shore, associated with isotherms of 17'C in winter and summer and with low temperatures in spring. Elsewhere the dominant pathway for this species was 1 instar in F, and 2 instars in F2. However, even the longest pathways were sometimes associated with stations near the coast. Greatest body lengths, especially in late furcilia stages, were found at stations where developmental pathways were generally short, while smaller larvae (in equivalent stages) were associated with longer pathways.

ABSTRACT. Bahía de los Ángeles is located on the Baja Californian coast of the Gulf of California, adjacent to Ballenas Channel. The bay receives a dynamic tidal influence from the channel but is protected by numerous islands. It is a highly productive bay that harbors a high diversity of species, some of them protected such as the whale shark (Rhincodon typus). This study describes the seasonal variability of major zooplankton taxa and copepod and cladoceran species between , 99.5% copepods) came from a sample collected south of Punta Arena, where two whale sharks were observed foraging. The shift in species composition during summer coincides with the predominance of easterly winds described in the literature inducing a reversed circulation and a probable transport of tropical species into the bay during summer and autumn (Centropages furcatus, Subeucalanus subcrassus, Acrocalanus longicornis, Temora discaudata, and Corycaeus amazonicus).Key words: zooplankton, copepods, cladocerans, Acartia clausi, Rhincodon typus. RESUMEN. Bahía de los Ángeles se localiza en la costa baja californiana del golfo de California, adyacente al Canal de Ballenas. La bahía recibe de éste una influencia dinámica de la marea y al mismo tiempo está protegida por numerosas islas. Es una bahía muy productiva y alberga una alta diversidad de especies, algunas de ellas protegidas como el tiburón ballena (Rhincodon typus). Este estudio describe la variación estacional de los grandes taxones de zooplancton y especies de copépodos y cladóceros entre mayo de 2003 y octubre de 2004. Los copépodos fueron dominantes durante el invierno y la primavera (83-99% de la abundancia del zooplancton), y experimentaron un dramático descenso en el otoño de 2003 (37-66%) y el verano de 2004 (25-45%). Los cladóceros fueron el segundo grupo más abundante, representado por Pseudevadne tergestina y Penilia avirostris. La primera especie se presentó todo el año con abundancia baja en invierno, mientras que la segunda se presentó sólo en verano y otoño. Otros taxones del holozooplancton contribuyeron con menos del 15% de la abundancia en la mayoría de las muestras, mientras que el merozooplancton con menos del 8%. No obstante, tanto en octubre de 2003 como de 2004 hubo una abundancia notable de equinodermos y otras larvas que contrasta con su escasez en otras temporadas. En el invierno de 2004 dominaron especies de copépodos templado-subtropicales como Calanus pacificus y Acartia tonsa. La alta abundancia de copépodos durante la primavera obedeció a Acartia clausi (mediana = 28,034 ind m -3 ). Sin embargo, la abundancia máxima de zooplancton (40,468 ind m -3 , 99.5% copépodos) provino de una muestra recolectada al sur de punta Arena, donde se avistaron dos tiburones ballena alimentándose. El cambio en composición de especies durante el verano coincidió con la predominancia de los vientos del este, descritos en la literatura, que inducen una reversión en la circulación y un probable acarreo de especies tropicales (Centropages furcatus, Subeucalanus subcr...

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