Mating compatibility, encystment and excystment characteristics of Alexandrium catenella from Chilean southern fjords

Resting cysts have been proposed to play an important role in the origin and initiation of A. catenella blooms in the seasonally variable Chilean southern fjords. However, it remains unclear whether endogenous or environmental mechanisms regulate the encystment timing and rate of Chilean strains. We investigated mating compatibility among 10 Chilean Group 1 A. catenella strains using the approach of Blackburn et al. (2001). Strains were crossed in all possible pairwise combinations and excystment rates assessed under a range of abiotic variables. Reproductive compatibility was highly variable among strains with high compatibilities among northern (Los Lagos) and southern (Magallanes) but not central (Aysen) strains. Encystment was synchronized in all pairwise crosses, with cyst production starting 26 days and terminating 45 days after inoculation. Cyst production was highly variable among crosses ranging from 7±1.3 to 316.9±20.5 cysts ml ^-1 (400 cell ml^-1 as inoculum). The dormancy period was estimated to be between 80 and 120 days with a maximum cumulative excystment of 60%. The following conditions enhanced excystment rate: Low temperature (10-12•C), high salinity (30 psu), N and/or P depletion, and low irradiance (20 microE m^-2 s^-1. These results suggest cysts may play a more important role in seeding A. catenella blooms than previously considered. The precise location of cyst beds need to be further defined.