Growth production of the euphausiid Nyctiphanes simplex at the coastal shelf off Magdalena, Bay, Baja California Sur, Mexico

Abstract

Growth production of the euphausiid Nyctiphanes simplex Hansen was examined off the southwest coast of the peninsula of Baja California, Mexico (Bahia Magdalena, 24 to 25° N), as a function of seasonal changes of temperature, zooplankton biomass, upwelling index, and regional ocean circulation. The data were collected during 4 oceanographic surveys from June to November 1986. High densities of N. simplex were found in the shallow coastal waters (<300 m). High production is maintained during late spring and summer, decreasing during autumn when stratification of the water column develops. We estimate the production attributable to growth of N. simplex on the coastal shelf was 273.42 mg m-2 yr-1 and showed a strong seasonal variation. This value was about 1/4 the value previously reported at Bahia Vizcaino in northern Baja California (28 to 29° N). Our data supports the hypothesis that there are strong latitudinal changes in regional production of this species along the west coast of Baja California. The production:biomass (P:B) ratio obtained for the period June to November 1986 was 6.99 yr-l. The maximum reproductive activity of N. simplex during spring and early summer at Bahia Magdalena appeared to be related to enhancement of the coastal upwelling.