Occurrence and predominance of the fish killer Cochlodinium polykrikoides on the Pacific coast of Costa Rica
AbstractWater samples were collected at several points along the Pacific coast of Costa Rica (10°00’N, 84°15’E) fortnightly from January 2003 to June 2004. During this period, dense red-ochre discolourations dominated by
Cochlodinium polykrikoides were observed, particularly over the dry season. In 2003, the highest cell density of 1.75 X 108 cells l–1 was observed in October. During April and June 2004, extensive blooms were
present, with the highest cell density (3.8 X 108 cells l–1) occurring in April. These blooms were accompanied by a strong fetid odour and large quantities of yellow foam. Fish mortalities also occurred near some coastal
areas. The observed discolourations tended to be associated with the strongest north-west winds on the North Pacific coast of Costa Rica. To date, blooms caused by C. polykrikoides have been increasing in
frequency and in extent. The previously unreported high cell densities and the increase in the duration and extent of these harmful algal blooms suggest that the environmental conditions have changed to the benefit
of C. polykrikoides over other phytoplankton species that usually bloom at that time of year. The fish mortalities associated with C. polykrikoides blooms are cause for concern, as are the possible environmental
changes contributing to the production of these extensive blooms.