Physical, chemical and zooplankton biomass variability (inshore-offshore) of Mexican Central Pacific during El Niño-La Niña 2010
The response of zooplankton, phytoplankton biomass (Chl-a concentration) and nutrients to the oceanographic variability in the Mexican Central Pacific was studied over three oceanographic surveys realized in 2010 (January, May and October). The highest zooplankton biomass (48 mL 1000 m-3) was registered in May when nitrites, nitrates, phosphates and silicates were also highest and mean Chl-a was 0.67 mg m-3. The lowest zooplankton biomass was registered in October, with a mean value of 25 mL 1000 m-3. Twenty-nine taxonomic groups of zooplankton were recorded, of which copepods contributed 71% of total abundance followed by chaetognaths (6%) and euphausiids (5%). Multivariate BEST test demonstrated that mixed layer depth and temperature at 25 m depth can explain the distribution of major zooplankton groups. The study area was influenced by El Niño conditions, which caused a seasonal shift. Coastal upwelling was evident until late summer, when geostrophic analysis showed a predominant SW component near the Jalisco coast. We suggest a possible top-down control of zooplankton grazing over phytoplankton, and acclimatization of both plankton groups to variability in environmental conditions induced by the transition from warm to cold ENSO phase.