The objectives of this dissertation were to describe the
complex oceanographic conditions around the Galápagos
Archipelago (eastern equatorial Pacific), their seasonal
variability, and their effects on patterns of cetacean
occurrence. The physical and ecological factors leading to a
plume of high phytoplankton biomass in the wake of the
Galápagos were investigated with principal component and
regression analyses of water-column climatologies and
satellite-derived ocean color. The results supported the
notion that this "island-mass effect" is fueled by upwelling
of the Equatorial Undercurrent (EUC) combined with natural
iron enrichment from the island platform. Seasonal
variability in long-term monthly fields of satellite-derived
seasurface temperature and ocean color was studied
through harmonic analysis and empirical orthogonal
function decomposition. Two annual cycles were identified
in both variables. The intensification of the Equatorial Front
and the South Equatorial Current in the second part of the
year was the dominant signal in the data. A secondary cycle
reaching its peak in the first part of the year was associated
with the topographically induced upwelling of the EUC on
the western side of the archipelago, and with advection of
upwelled Panamá Bight water on the eastern side. The
occurrence of nine cetacean species (including seven small
and medium-sized delphinids, the sperm whale, and the
Bryde’s whale) in relation to environmental variability
around the archipelago was described. Seasonally
persistent sectors of the archipelago characterized by the
presence of distinct species assemblages of stratified,
upwelling, and nearshore environments were identified
through cluster and indicator species analysis. The
dominant pattern in species distribution, as extracted by a
nonmetric multidimensional scaling procedure, was well
correlated with the main environmental gradient (described
by the degree of water-column stratification, chlorophyll-a
concentration, and distance from the islands). The
collective results of this study indicate that the ocean
environment surrounding the Galápagos Archipelago is
strongly influenced by equatorial flows. However, the
archipelago also introduces a disturbance to these flows,
creating localized and persistent conditions that favor the
establishment of distinct biological communities around
the islands.

More information is available at http://www.pfeg.noaa.gov/
~dpalacio