VARIATION IN THE SURFACE CURRENTS IN THE PANAMA BIGHT DURING EL NIÑO AND LA NIÑA EVENTS FROM 1993 TO 2007

Abstract

Climatic anomalies have changed the ocean circulation pattern and thus the demographic connectivity. However, in many geographical regions there is insufficient evidence of this change. Therefore, comparisons were made between neutral years and years of El Niño and La Niña with moderate intensity, for the North Equatorial Counter Current (NECC), the South Equatorial Current (SEC), the Coastal Current (CoaC) and the main anticyclonic eddy in the Panama Bight. Daily dynamics topography data of the Maps of Absolute Dynamic Topography (MADT) provided by AVISO and daily wind stress data provide by the European Centre for Medium Range Weather (ECMWF) were used to calculate the speed of surface currents (multi-year, quarterly average), during months with the highest number of eggs and larvae released by the species with a pelagic phase (Sept-Nov). It was found that the speed magnitude for the three oceanic currents was statistically different among the compared events, except for the anticyclonic eddy; obtaining higher values of speed for neutral years in relation to years with El Niño or La Niña for the NECC, for the SEC higher values for La Niña years, followed by neutral years and a moderate El Niño years; for the CoaC higher velocity for neutral and La Niña years but the lowest for El Niño years; and a tendency of higher values in La Niña years for the anticyclonic eddy. Additionally, the number of eddies increased in moderate El Niño years. The results suggest that the decreased velocity of the NECC and the potential barriers created by the cyclonic eddies and the anticyclonic eddy near the South American coast could diminish the passive dispersal of larvae and the potential functional connectivity between the Western, Central and Eastern Tropical Pacific. Therefore, there are implications at the evolutionary, biogeographic, and ecologic levels (dispersion rates and population rescue effect). In contrast, during La Niña the SEC could favor teleplanktonic larval transport to the Central Pacific, material which is exported from the South American coast by CoaC, aided by the anticyclonic eddy. In conclusion, anomalous climatic events alter the velocity of oceanic currents in the Panama Bight; consequently these could change the functional potential connectivity from September to November.