Zooplankton abundance variability in Magdalena Bay, Baja California Sur, Mexico (1997-2001)

Abstract

Zooplankton were studied from 16 oceanographic surveys carried out in Magdalena Bay, Baja California Sur, Mexico, between August 1997 and March 2001. Twenty-six taxonomic groups were identified, the most abundant and frequent of which were copepods and chaetognaths. In 2000-2001, the number of zooplankton groups tended to decrease by 10 to 20. Both zooplankton biomass and copepod abundance declined, unlike chaetognaths, which increased slightly. Fluctuations in zooplankton abundance were independent of the chlorophyll-a concentration, whereas the maximum zooplankton abundances were associated with changes in the sea surface temperature. The seasonal zooplankton abundance cycle in Magdalena Bay indicated that, in winter, the averaged was than 65,000 ind 100 m-3, a value that increased to more than 99,000 ind 100 m-3 in spring, remained around 100,000 ind 100 m-3 in summer, and decreased rapidly to nearly 40,000 ind 100 m-3 in autumn.