Abstract

Resting cysts play an important role in the origin and initiation of Alexandrium dinoflagellate blooms in different coastal environments. Alexandrium catenella causes major economic impacts for the Chilean shellfish and fish farm industries, but the environmental conditions that regulate the encystment timing and cyst production rate in the seasonally variable fjords are poorly understood. We investigated mating compatibility and genetic relationships among 10 Chilean strains of A. catenella Group 1 using rDNA-ITS and LSU-rDNA sequences. Strain crossing experiments in all possible pairwise combinations showed variable reproductive compatibility among strains with high compatibilities among northern (Los Lagos) and southern (Magallanes) but not central (Aysén) strains. However, these mating differences were not reflected in the identical LSU-rDNA and rDNA-ITS sequences observed among the strains. Encystment was synchronized in all pairwise crosses, with cyst production starting 26 days and terminating 45 days after inoculation. Cyst production was variable among crosses ranging from 7±1.3 to 316.9±20.5 cysts ml-1. The successful pairwise crosses performed with strains from the northern Chilean fjords do not explain the low concentrations of cysts detected in this area. Instead, these low cyst concentrations might be the result of local circulation patterns leading to a net flux offshore.