Zooplankton patchiness associated with two harmful algal blooms in Bahia de Banderas

Abstract

Routine samplings of the Bahia de Banderas plankton communities allowed to detect two Mirionecta rubra y Pseudonitzschia sp red tides events during 2011. In order to identify the most representative zooplankton populations associated with the first event, fourteen standard zooplankton tows were made, including two replicates in the reddest waters. Tows were made with a standard net of 40 cm mouth diameter, and 335 µ mesh size. The highest zooplankton abundance was not recorded in the most colored waters. On the contrary, a sample collected in the most colored waters during the second event revealed a high zooplankton abundance of 5 million ind/m³, which is an unusual density value for the epipelagic zooplankton in the Mexican Pacific. This abundance was at least three orders of magnitude higher than those recorded in other epipelagic zooplankton patches in the Pacific Ocean coastalzone. The zooplankton community structure of both events was dominated by the calanoid copepod Acartia tonsa. Red tide events persisted locally until the end of April, when stranded globe fish were detected on the beach. The sequence of these events appears to be associated with the occurrence of upwellings previously reported in the Cabo Corrientes area.