Unusual Larval Growth Production of Nyctiphanes simplex in Bahía de La Paz, Baja California sur, México

Abstract

ABSTRACT Nyctiphanes simplex is one of the few neritic euphausiid species in the world. This species frequently dominates the nearshore waters of the Gulf of California, the transition zone of the California Current, and the eastern tropical Pacific off Ecuador and Peru. It has a high production in coastal and upwelling waters and plays an important role in the trophodynamics of these areas. This work examines the larval growth production (Pg) of Nyctiphanes simplex in Bahfa de La Paz, Baja California Sur, Mexico. The data were collected during 7 oceanographic expeditions from February-August 1990. Except for August, larval growth production remained at high levels in the bay. Daily and annual growth production for both transects were estimated. The mean annual larval Pg value for the entire area was 195.7 mg·dw·m-3 yr-1, the highest value recorded for the genus Nyctiphanes. The annual mean P:B ratio (defined as the ratio of annual production to average annual biomass for a particular species) for the bay was 35, using data representing mostly the youngest part of the population, which exhibits the highest growth rates (individuals < 6 mm). These values are related to the reproductive period of the species and to regional biological and oceanographic features present in this bay. We consider these values of larval Pg as an index that in Bahia de La Paz the production of Nyctiphanes simplex is comparable to that of upwelling regions and that the bay functions as a nursery and feeding area for many other species, such as sardines, whales, manta rays, and zooplankton.