Seasonal succession of zooplankton taxonomic group assemblages in surface waters of Bahia de Navidad, Mexico (November 2010-December 2011)

The seasonal succession of the abundance of 19 zooplankton groups collected every two weeks (but averaged monthly) during November 2010-December 2011 at a coastal monitoring station (Bahia de Navidad, 19 degrees 09'03 '' N, 104 degrees 44'50 '' W) were analyzed as a function of seasonal hydro-climatic variability. Coastal upwelling events caused cold conditions and a shallow (> 20 m) upper boundary of the hypoxic strata (< 1.5 ml L-1) during most of the year except between June-August when stratified conditions prevailed. Copepods (66%), decapod larvae (11%), amphipods (5%), ostracods (4%), cladocerans (4%), fish eggs (3%), euphausiids (2%), chaetognaths (1.5%) and pteropods (1.5%) accounted for 95% of the total zooplankton abundance. Total abundances were highest from November 2010 to May (geometric mean 1173 ind m(-3)), gradually decreasing to the lowest values in June-August (28 ind m(-3)), and increasing again to moderate abundances during September-December 2011 (405 ind m(-3)). The number of zooplankton taxonomic groups increased during May-June (mixed-to-stratified transitional period). The redundancy analysis showed a clear seasonal succession of zooplankton relative abundance and community structure, grouping sample units seasonally per hydro-climatic periods (mixed, semi-mixed, and stratified). Temperature and salinity at 10 m, mixed layer depth, and coastal upwelling index were the main environmental variables that influenced the zooplankton taxonomic group succession during the three hydro-climatic periods. We conclude that during the study period the composition and abundance of the main taxonomic groups inhabiting this tropical coastal region is mainly explained by the seasonal variation of intensity and duration of local upwelling events.