Dinoflagellates

 What is a dinoflagellate?

Dinoflagellates are microscopic unicellular protists. Approximately half are autotrophs that have chloroplasts and are photosynthetic, while the other half is not photosynthetic and consumes organic material instead.

Dinoflagellates are motile, and depend on flagella that extend from their bodies in order to move. They have two flagella; a transverse flagellum, contained in the groove in the equator of the organism, is used for forward and spinning motions, while another flagellum trailing behind it is used for steering purposes, like a rudder.  

 Habitats

90% of all dinoflagellates are marine planktons, which means they inhabit oceans, seas, and are even common in freshwater lakes, rivers, and bogs.

Some dinoflagellates can be found on other organisms in a symbiotic relationship. These Dinoflagellates are called zooxanthellae, and can be found on many marine invertebrates, such as a sea sponge, coral, and jellyfish.

 Life Cycle

1) Binary fission: Most dinoflagellates have a dinokaryotic nucleus throughout their entire life cycle, and are usually haploid, so they reproduce primarily through binary fission.

2) Sexual reproduction can also take place, when two individuals fuse together to form a zygote before going through meiosis later on.

3) Planozygote: When conditions are not favourable, two vegetative cells fuse to form this.

4) Hypnozygote: A stage where the organism takes in excess oil and fat and the shell hardens, much like hibernation.

5) Planomeiocyte: When the dinoflagellates break out of the shell and are in a temporary stage called planomeiocyte, before returning as normal dinoflagellates.

The life cycle of a dinoflagellate.

Reproduction


Dinoflagellates are primarily asexual, and go through asexual cell division - mitosis. This results in two identical copies of the dinoflagellate. The covering, or theca, may be shed and regrown in the daughters, or it could be divided - each daughter receiving half or growing half. If by chance the cells do not separate after dividing, they grow into filaments.

Not all dinoflagellates reproduce asexually. Some reproduce sexually, where two individuals of dinoflagellate fuse together to form a zygote. This zygote either remains mobile or form a resting dynocyst, before undergoing meiosis that will result in new haploid cells.


Bioluminescence 

Dinoflagellates are sometimes called Pyrrhophyta , meaning "fire plants". Some species are capable of chemically creating their own light in bioluminescence. They will produce these lights when disturbed or agitated - this was probably used to scare away predators. These lights are more visible when they are "blooming" - when there are more concentrated amounts of dinoflagellate.

 

 An example of a useful advantage dinoflagellates get using bioluminescence.

 

 Dinoflagellate Blooms

Why should we humans care so much about dinoflagellates?

These microscopic marine organisms are considered to be one of the most primitive eukaryotes, but they are important primary producers and are an important part of the food chain. Other than that important fact, dinoflagellates are responsible for a strange phenomenon called "red tide". This event occurs during the warmer season; from mid to late summer. During these times, upwelling occurs in oceans, and the nutrients from the bottom of the ocean reach the surface, and cover the surface plankton in it. This surplus of nutrients begins a "bloom" of photosynthetic dinoflagellates, where they have drastic increases in the density of the population - up to 20 million dinoflagellates per litre! 

At these densities, some dinoflagellates produce neurotoxins, which are harmful to marine life. The marine animals that feed on dinoflagellates consume the neurotoxins, which can result in massive death in fish, shellfish, and any other marine life. If the neurotoxins do not kill the fish, they still carry the toxins in their bodies, and when humans catch fish and marine life as food, we consume those toxins as well. The toxins can prove to be fatal to humans as they are to marine life.

Some of the causes for red tide are natural, while some are caused by human activities. Any activity that results in movement of certain ocean currents cause red tides. Human inputs of phosphates and warmer global temperatures are a few causes we are suspecting that results in "red tides". This is probably why we have interest in researching and studying dinoflagellates for both medical and economic effects.

Long exposure image of red tide bioluminescence taken at midnight at a Carlsbad, California beach during the 2005 red tide event.