Dispersion and development patterns in larvae of Nyctiphanes simplex (Euphausiacea) in the upwelling region off Baja California

Abstract

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.