A preliminary study of the formation of a third category of cysts by a toxigenic dinoflagellate, Alexandrium fundyense in response to elevated concentrations of ammonium chloride

Exposure of exponentially growing cells of a toxigenic dinoflagellate strain, Alexandrium fundyense, to ammonium chloride concentrations comparable to levels of ammonia observed in Bay of Fundy waters induced formation in a few days of large numbers of double-walled, circular cysts (termed forced cysts). The A. fundyense forced cysts were distinctly different from the asexual pellicle cysts, and the sexual resting cysts (hypnocysts) described by Anderson and Wall (1978). The circular shape of these forced cysts and their relatively rapid formation suggest that they were not products of fusion while their resistance to adverse conditions and, when returned to optimal conditions, their subsequent rapid germination to form viable cultures within 14 days, point to an important long-term survival role in response to rapidly changing nutritional and environmental circumstances as well as in the waxing and waning of local toxic dinoflagellate blooms. The relative ease of producing the forced cysts and their fairly rapid germination suggest that these cysts could be suitable vehicles for investigations of the physiology and biochemistry of encystment and excystment in the species producing them.Chemical analyses of forced cysts harvested from cultures of this A. fundyense strain showed large variabilities in selected storage products: iron ranged from 0.03 pg to 17.40 pg Fe/cyst corresponding to 0.04–61.25% of the cyst dry weight; nitrogen levels ranged from 109 pg to 3183 pg/cyst and phosphorus ranged from 0.55 pg to 5.70 pg/cyst. Total paralytic shellfish poisons for these A. fundyense cysts consisted of the same toxins apparent in the vegetative cells, i.e. C1C2 toxins, GTX 2/3, saxitoxin and neosaxitoxin, and ranged from 4.4 fmol to 333 fmol/fg cyst dry wt.

► Enrichment with ammonium chloride, of Alexandrium fundyense cultures gave rise to “forced cysts”.
► These cysts were quite different from either the pellicle cyst or the hypnocyst.
► Selected storage products i.e. iron, nitrogen and phosphorus varied.
► Toxin composition for these cysts consisted of the same toxins apparent in the vegetative cells.
► These cysts play an important long-term survival role in response to environmental circumstances.