Copepod community structure in Bahia de Banderas during the 2008-2009 La Niña and their transition to the 2009-2010 El Niño.

Abstract

In order to investigate the taxonomic copepod community structure and its relations with the climate conditions in the Pacific Ocean, bimonthly samples were made between February 2009 and April 2010. Samples were collected by vertical tows between the surface and the vicinity of the bottom with a 40-cm mouth diameter and 335 µ mesh size standard zooplankton net. At the beginning of the study water temperatures were low indicating that La Niña conditions prevailed in the bay. However, at the end of June, 2 °C warmer waters associated with El Niño 2009-2010 arrival were detected. These conditions persisted at least until February 2010, and by April water temperature returned to normal. 57 copepods species were recorded, being Acartia tonsa, Acartia lilljeborgi, Oithona plumífera, Centropages furcatus and Nannocalanus minor the most representative species. These five populations accounted most of the 90 % of the collected animals. Cluster and non-metric Multidimensional Scaling (NMDS) methods show two groups that seem to be associated with La Niña and El Niño conditions. The Anosim indicates that these assemblages were different (R = 0.411; p = 0.01 %). Simper analysis indicated that A. tonsa was the dominant population (85.4 %) at the end of the 2008-2009 La Niña; this population was followed by A. lilljeborgi (7.9 %) and Pareucalanus subtenuis (2.5 %). During the El Niño the dominance of A. tonsa disappeared (32 %) while Oithona plumífera, Temora discaudata y Undinula darwinii increased. At the end of El Niño, species diversity and richness also changed. At the end of the 2008-2009 La Niña conditions, 40 species were recorded, while during El Niño the species richness increased to 52 species.