Environmental forcing on zooplankton distribution in the coastal waters of the Galápagos Islands: spatial and seasonal patterns in the copepod community structure

Abstract

The oceanographic setting of the Galápagos Archipelago results in a spatially diverse marine environment suitable for a variety of species with different climatic requirements. The goal of this study is to demonstrate that the community of zooplankton in the Galápagos is highly structured by regional differences in productivity patterns and advective sources. Results are mostly based on biodiversity patterns of the copepod community collected over the Galápagos shelf between 2004 and 2006. Two contrasting marine environments were observed: a nutrient-rich upwelling system with a shallow mixed layer and a diatom-dominated phytoplankton community in the west, and a non-upwelling system with a deeper mixed layer, lower surface nutrient concentrations, and a phytoplankton community dominated by small cells in the east. These conditions drive spatial structuring of zooplankton that varies seasonally, with 3 distinct copepod communities separated geographically in western, central, and southeastern regions. The western upwelling region has a high-abundance and low-diversity community, whereas the non-upwelling eastern region has a lower-abundance and higher-diversity community. The eastern community is further differentiated into central and southeastern regions, the former with tropical species advected from the north, the latter with temperate species advected from the south. During the warm season, when the equatorial front moves south, species typical of the central region spread southwest across the archipelago. This is the first taxonomically comprehensive list of copepod species for the Galápagos Islands. A total of 164 copepod species are identified, including 22 species previously unreported from the Eastern Tropical Pacific.