Dinoflagellates: A Brief Overview
Though most dinoflagellates are marine planktons, some of them are also found in freshwater ecosystems. They are known to possess the characteristics of both flora and fauna and serve as a crucial link in the food chain.
Notably, there are over 4500 species of dinoflagellates, half of which tend to be autotrophs. On the other hand, the rest are mostly autotrophs which avail nutrients through phagocytosis. Furthermore, they are diverse in their form and comprise a significant share of the bioluminescent dinoflagellates.
Keeping this information in mind, let us proceed to find out more about these unicellular protists in detail.
Classification of Dinoflagellates
A per the 5-kingdom scheme, algae and protozoa belong to Kingdom Protista. What is noteworthy is that they are distinct from protozoa because they are photosynthetic.
The Subgroups of Phylum Dinoflagellates Include
This Table Below Highlights The Scientific Classification of Dinoflagellates
Some of The Most Common Genera of Dinoflagellates Include
Structure of Dinoflagellates
These are some important pointers about dinoflagellates structure
They are unicellular organisms with an eukaryotic cell.
They have two distinct flagella which are dissimilar from one another.
Depending on pigment present in their cell, they can be red, blue, brown, yellow or green.
Their cell has a complex covering which is known as amphiesma, and it has flattened vesicles known as alveoli.
Alveoli are present in the plasma membrane and can contain cellulose plates that are high in silicates.
The cell has membrane-bound organelles like food vacuoles, mitochondria, Golgi bodies and endoplasmic reticulum.
Dinoflagellates’ nucleus is known as dikaryon, and its nucleus membrane has a chromosome.
The nucleus lacks histones and has a fibrillar appearance.
DIY: Study the structure of dinoflagellate carefully. Draw a dinoflagellate diagram and label it accurately.
Characteristics of Dinoflagellates
Dinoflagellates characteristics are as follows –
Most dinoflagellates are marine planktons, but some are also found in freshwater.
Their distribution depends on the pH level, temperature and depth of the aquatic ecosystem.
Their flagella are responsible for locomotion and facilitate a spinning top-like motion.
A large segment of dinoflagellates is bioluminescent and tend to emit blue-green light.
Dinoflagellates multiply rapidly and often lead to population explosions.
A toxin is released by the blooms, which is considered to be extremely poisonous.
The toxic algal bloom is known as red tide, and the causative agent of red dinoflagellates include Karenia Brevis, Alexndrium fundyense, etc.
They possess an organelle called eyespot, which is light-sensitive and comprise lipid droplets. It helps their sense of direction concerning light.
Some genera possess ocellus, which is a rare structure.
Dinoflagellates store food in the form of starch.
Pustule, which is a non-contractile vacuole facilitates floatation and osmoregulation in dinoflagellates.
Fun Fact: Under ideal conditions, the population of dinoflagellates may reach as much as 60 million organisms for every litre of water.
Reproduction in Dinoflagellates
These organisms mostly reproduce asexually through cell division, and cysts of dinoflagellates can be found in a significant number. However, sexual reproduction is common in some genera, which are mostly anisogamous or isogamous.
Notably, dinoflagellates that reproduce sexually may go through a resting phase and turn into a hypnozygote. Also, in the cysts, hatchlings go through meiosis for producing haploid cells.
Furthermore, the lifecycle in ceratium, woloszynskia and gymnodinim involves zygotic meiosis, while in case of noctiluca it involves gametic meiosis.
Bioluminescence is a characteristic feature in over 18 genera of dinoflagellates. The feature is attributed to a chemical reaction that takes place in the organisms’ body.
During the said reaction, the light-producing biochemical luciferin is oxidised by catalytic enzyme luciferase. The reaction emits light and produces an ineffective compound called oxyluciferin.
What is noteworthy is that the reaction is dependent on pH, which means a drop in pH would drive the luciferin to bind with luciferase owing to a change in the enzyme’s shape. However, it must also be noted that different genera of dinoflagellates may use these biochemicals in different ways.
These organisms use bioluminescence to defend themselves against predators and also to communicate with one another.
Examples with ecosystems with bioluminescent dinoflagellates include Montego Bay, Indian River Lagoon, Puerto Rico, etc.