La marea roja causada por el dinoflagelado Alexandrium tamarense en la costa Pacífica colombiana (2001)

Abstract

From April 26 th to May 15 th 2001, a large algae bloom was observed off Tumaco Bay on the Pacific coast of Colombia. This was the first harmful algae bloom (HAB) reported in the region, and reached Gorgona Island, about 120 km north. A year later, starting March 2002, an offshore HAB developed from Cabo Corrientes North to Solano Bay. The typical abundance during the blooms reached 7.5 x 10 6 cells l -1 for the 2001 event and 1.6 x 10 6 cells l -1 for the 2002 event. During both events, low temperature and high salinity were recorded. Typical measurements in the area are 27-27.5°C and 30-31.5 psu. Values observed during the two events were 24-24.6°C and 33-34 psu; 3°C below normal and more than 2.5 psu above average values. These conditions are indicative of local upwelling processes at the time of the events. On both occasions, cells corresponding to the Alexandrium catenella/fundeyense/tamarense complex represented 99-100% of the biomass. It was difficult to differentiate the cells from A. catenella, but the presence of short chains of only 4 cells (single cells represent- ed most of the biomass) was suggestive of A. tamarense. Shape, dimensions, and detailed structure of the apical pore complex, first apical plate, posterior sulcal plate, and position of the ventral pore on plate 1' of cells were consistent with the description of A. tamarense, which has not been reported in the tropical East Pacific. The Control Center of Pacific Contamination of the Maritime General Direction of the Colombian Navy has been monitoring the area since 1994 without finding this species or HABs. This leads us to consider the two events as caused by recently introduced species, where local upwelling processes favor permanent and cyclic HABs. However, during these two events, there were no reports of effects on marine biota or of human poisoning, prob- ably because the blooms occurred some distance offshore and far from exploited shellfish beds.