Life Cycle of a Dinoflagellate

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Algae usually reproduce by asexual fission: One cell grows and then divides into two cells, then two into four, four into eight, and so on. When growth is unchecked by environmental conditions—such as grazing by animals or a shortage of nutrients or light—harmful algae populations can accumulate to visually spectacular but catastrophic levels.

For some species, a decline in available nutrients provokes a switch to sexual reproduction and a new life stage. When they sense that their boom times are coming to an end, the algae form thick-walled, dormant cells called cysts that settle to bottom sediments. These cysts can survive for years, allowing a species to withstand nutrient starvation, extreme winter temperatures, or even ingestion by animals. When favorable conditions resume, the cysts rupture, germinate, and populate the water column with a new generation of photosynthetically active cells primed for another bloom.

The cyst stage represents an effective strategy for survival and dispersal. With every switch into the cyst stage, a bloom can be carried into new waters by ocean currents, fish, or even humans (via ballast water discharge) and then deposited as a “seed” population that colonizes a new area.

Last updated: July 31, 2012