Larval drift and population structure of the pelagic phase of Pleuroncodes planipes (Stimpson) (Crustacea: Galatheidae) off the southwest coast of Baja California, Mexico

Reproductive areas, larval and postlarval drift, and population structure of the red crab Pleuroncodes planipes (Stimpson) are described using samples obtained off the southwest coast of Baja California in May, June, August, and November 1986, July 1988, and September 1993. The highest abundance of larval and postlarval stages were found in May. Based on the ages of the most abundant postlarval stages, the most intense reproductive period was probably in January and February. The larval production recorded June to November indicated sporadic reproduction. We confirmed that the nearshore regions located near Bahia Magdalena 24° N and Punta Eugenia 28° N are the primary nursery areas. Seasonal hatching areas were in the vicinity of upwelling regions. Major production of larval stages starts in the south. At the end of the reproduction season, the highest abundance is in the north suggesting this species has a seasonal reproduction cline keyed to the normal upwelling cycle along the west coast of Baja California. From the hatching areas, a larval drift caused by offshore surface transport, in turn caused by the upwelling, was seen. A one-celled cross-shelf circulation is proposed to explain the offshore larval drift at the west coast of Baja California. This process could play an important role in the recruitment of postlarval stages to the adult epipelagic population. Two size groups of adults were found in the water column. Both groups were found simultaneously only inshore and during the seasonal reproductive months (spring). The group of largest size found inshore are individuals of the benthic phase that may have migrated into the pelagic zone for reproduction. Using data of this study and the current available information, a conceptual model of the life history of P. planipes along the west coast of Baja California is proposed.