They may feed on other dinoflagellates, algae, eggs and larvae of plankton or may depend on photosynthesis or both.
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Cyst
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The cyst form is dormant, may last for years and may be found in sediment. The cyst is triggered to germinate when conditions are favorable and oxygen is available.
Temperature and light levels can trigger germination of cysts. The cysts open to release a swimming cell. That cell reproduces through division.
One cell can form several hundred over a period of weeks. With the proper mix of conditions and nutrients, exponential growth may occur; a large bloom may contaminate species eaten as seafood.
Gametes
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Algae may reproduce asexually or sexually. In asexual reproduction, only one cell is needed. That cell divides, creating two cells, then they both divide, creating four. The reproductive process will continue as long as the environmental conditions support it.
As conditions wane, growth slows to a stop. Gametes form, and one or more of the hard coverings (theca) of the cell, made of cellulose, may be lost as the gametes pair.
Zygote
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When two gametes combine to form a single cell, it produces a zygote (it is from the zygote phase that a cyst develops). The coverings are then regenerated.
Waning conditions provide the stimulus that triggers the cell to change to sexual reproduction. These may involve temperature, light, nutrients or a combination of any of the three. Under natural conditions, late summer, fall and the end stages of blooms are times when sexual reproduction will occur.
Developing Cyst
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Cell activity slows, then stops. The flagella fall away and the cyst develops underneath the theca. Cysts have thick-walled cells to protect their contents. The cysts then rain down into sediment where they await a trigger.
Cyst stages allow the cell to survive ingestion by fish, animals or humans and endure harsh temperatures and lack of food.
Biology
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The dinoflagellate contains organelles (which are light sensitive) and an eyespot. Choloroplasts, a nucleus, a pusule, mitochondria, vacuoles, a Golgi body and endoplasmic reticulum of both rough and smooth types are all a part of the cell.
The creatures also feature two flagella; the longitudinal flagellum (used for direction) aims toward the posterior and the transverse flagellum forms a lateral circle. They are often set into grooves, the sulcus (longitudinal) and cingulum (transverse). The action of the transverse flagellum causes a whirling motion from which the cell gets its name.
Blooms
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Human introduction of phosphates into water sources and global warming are blamed for blooms of algae occurring more frequently.
Not all blooms are dangerous, but some dinoflagellate species can produce neurotoxins, killing fish and becoming concentrated in shellfish who filter the water from the bloom. Blooms may be colorful or colorless, may be lethal, only sicken or be totally harmless.
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