Habitats Dinoflagellates are found in all aquatic environments: marine, brackish, and fresh water, including in snow or ice. They are also common in benthic environments and sea ice.
Endosymbionts All
Zooxanthellae are dinoflagellates and most of them are members within Symbiodiniaceae (e.g., the genus
Symbiodinium). The association between
Symbiodinium and reef-building
corals is widely known. However, endosymbiontic
Zooxanthellae inhabit a great number of other invertebrates and protists, for example many
sea anemones,
jellyfish,
nudibranchs, the giant clam
Tridacna, and several species of
radiolarians and
foraminiferans. Many extant dinoflagellates are
parasites (here defined as organisms that eat their prey from the inside, i.e.
endoparasites, or that remain attached to their prey for longer periods of time, i.e. ectoparasites). They can parasitize animal or protist hosts.
Protoodinium, Crepidoodinium, Piscinoodinium, and
Blastodinium retain their plastids while feeding on their zooplanktonic or fish hosts. In most parasitic dinoflagellates, the infective stage resembles a typical motile dinoflagellate cell.
Nutritional strategies Three nutritional strategies are seen in dinoflagellates:
phototrophy,
mixotrophy, and
heterotrophy. Phototrophs can be
photoautotrophs or
auxotrophs.
Mixotrophic dinoflagellates are photosynthetically active, but are also heterotrophic. Facultative mixotrophs, in which autotrophy or heterotrophy is sufficient for nutrition, are classified as amphitrophic. If both forms are required, the organisms are mixotrophic
sensu stricto. Some free-living dinoflagellates do not have chloroplasts, but host a phototrophic endosymbiont. A few dinoflagellates may use alien chloroplasts (cleptochloroplasts), obtained from food (
kleptoplasty). Some dinoflagellates may feed on other organisms as predators or parasites. Food inclusions contain bacteria, bluegreen algae, diatoms, ciliates, and other dinoflagellates. Mechanisms of capture and ingestion in dinoflagellates are quite diverse. Several dinoflagellates, both thecate (e.g.
Ceratium hirundinella, and
Kofoidinium spp.), draw prey to the sulcal region of the cell (either via water currents set up by the flagella or via pseudopodial extensions) and ingest the prey through the sulcus. In several
Protoperidinium spp., e.g.
P. conicum, a large feeding veil—a pseudopod called the pallium—is extruded to capture prey which is subsequently digested
extracellularly (= pallium-feeding).
Oblea,
Zygabikodinium, and
Diplopsalis are the only other dinoflagellate genera known to use this particular feeding mechanism.
Gymnodinium fungiforme, commonly found as a contaminant in algal or ciliate cultures, feeds by attaching to its prey and ingesting prey cytoplasm through an extensible peduncle. Two related genera,
Polykrikos and
Neatodinium, shoot out a harpoon-like organelle to capture prey. Some mixotrophic dinoflagellates are able to produce neurotoxins that have anti-grazing effects on larger copepods and enhance the ability of the dinoflagellate to prey upon larger copepods. Toxic strains of
Karlodinium veneficum produce karlotoxin that kills predators who ingest them, thus reducing predatory populations and allowing blooms of both toxic and non-toxic strains of
K. veneficum. Further, the production of karlotoxin enhances the predatory ability of
K. veneficum by immobilizing its larger prey.
K. armiger are more inclined to prey upon copepods by releasing a potent neurotoxin that immobilizes its prey upon contact. When
K. armiger are present in large enough quantities, they are able to cull whole populations of their copepod prey. The feeding mechanisms of the oceanic dinoflagellates remain unknown, although pseudopodial extensions were observed in
Podolampas bipes.
Pigments in dinoflagellates Dinoflagellates possess a distinctive suite of photosynthetic pigments that allow them to survive and grow in a variety of aquatic environments. Like other phytoplankton, many dinoflagellates contain chlorophyll a and chlorophyll c, which are essential for photosynthesis and light energy capture. However, unlike green algae and higher plants, they lack chlorophyll b. Instead, they utilize chlorophyll c2, which is more efficient for absorbing blue-green light, making them well adapted to low-light or deeper water conditions. These pigments, along with carotenoids, contribute to the characteristic coloration of dinoflagellates, which can range from golden-brown to red. A unique pigment in dinoflagellates is
peridinin, a specialized carotenoid that plays a key role in light harvesting and energy transfer to chlorophyll a. Peridinin is highly efficient in capturing blue light, which penetrates deeper into the water column, giving many dinoflagellates a competitive advantage in stratified or turbid environments. Additionally, dinoflagellates contain other carotenoids such as diadinoxanthin and dinoxanthin, which play important roles in photoprotection by dissipating excess light energy and preventing oxidative stress under high irradiance. These pigments are necessary for photoacclimation, allowing dinoflagellates to survive under fluctuating light conditions. Not all dinoflagellates rely solely on photosynthetic pigments for energy. Many species are heterotrophic or mixotrophic, meaning they can acquire nutrients through both photosynthesis and predation. Symbiotic dinoflagellates, such as Symbiodinium, play an important ecological role by forming mutualistic relationships with corals, where their pigments drive photosynthesis and energy production that sustain coral reef ecosystems. The unique pigment composition of dinoflagellates also contributes to large-scale phenomena such as harmful algal blooms and red tides, where high concentrations of pigmented cells cause dramatic discoloration of coastal waters and can produce toxic effects.
Blooms Introduction Dinoflagellate blooms are generally unpredictable, short, with low species diversity, and with little species succession. The low species diversity can be due to multiple factors. One way a lack of diversity may occur in a bloom is through a reduction in predation and a decreased competition. The first may be achieved by having predators reject the dinoflagellate, by, for example, decreasing the amount of food it can eat. This additionally helps prevent a future increase in predation pressure by causing predators that reject it to lack the energy to breed. A species can then inhibit the growth of its competitors, thus achieving dominance.
Harmful algal blooms Dinoflagellates sometimes bloom in concentrations of more than a million cells per millilitre. Under such circumstances, they can produce toxins (generally called
dinotoxins) in quantities capable of killing fish and accumulating in filter feeders such as
shellfish, which in turn may be passed on to people who eat them. This phenomenon is called a
red tide, from the color the bloom imparts to the water. Some colorless dinoflagellates may also form toxic blooms, such as
Pfiesteria. Some dinoflagellate blooms are not dangerous. Bluish flickers visible in ocean water at night often come from blooms of
bioluminescent dinoflagellates, which emit short flashes of light when disturbed. A red tide occurs because dinoflagellates are able to reproduce rapidly and copiously as a result of the abundant nutrients in the water. They contain
toxins that affect surrounding marine life and people who consume them. A specific carrier is
shellfish, which can introduce both nonfatal and fatal illnesses. One such poison is
saxitoxin, a powerful
paralytic neurotoxin. Human inputs of
phosphate further encourage these red tides, so strong interest exists in learning more about dinoflagellates, from both medical and economic perspectives. Dinoflagellates are known to be particularly capable of scavenging dissolved organic phosphorus for P-nutrient, several HAS species have been found to be highly versatile and mechanistically diversified in utilizing different types of DOPs.
Bioluminescence '' in the yacht port of
Zeebrugge, Belgium , Vieques, Puerto Rico At night, water can have an appearance of sparkling light due to the bioluminescence of dinoflagellates. More than 18 genera of dinoflagellates are bioluminescent, and the majority of them emit a blue-green light. These species contain
scintillons, individual cytoplasmic bodies (about 0.5 μm in diameter) distributed mainly in the cortical region of the cell, outpockets of the main cell vacuole. They contain
dinoflagellate luciferase, the main enzyme involved in dinoflagellate bioluminescence, and
luciferin, a chlorophyll-derived tetrapyrrole ring that acts as the substrate to the light-producing reaction. The luminescence occurs as a brief (0.1 sec) blue flash (max 476 nm) when stimulated, usually by mechanical disturbance. Therefore, when mechanically stimulated—by boat, swimming, or waves, for example—a blue sparkling light can be seen emanating from the sea surface. Dinoflagellate bioluminescence is controlled by a circadian clock and only occurs at night. Luminescent and nonluminescent strains can occur in the same species. The number of scintillons is higher during night than during day, and breaks down during the end of the night, at the time of maximal bioluminescence. The luciferin-luciferase reaction responsible for the bioluminescence is pH sensitive. Some species also possess the luciferin binding protein which binds to luciferin before acidification to protect it from autoxidation, and then releases it upon the structural change to make luciferin active. The "oxygen defense hypothesis" suggests that bioluminescence first evolved in response to the Great Oxidation Event when oxygen accumulated in the atmosphere. Organisms had to adapt to oxidative stress from reactive oxygen species, resulting in light emission as a byproduct. Although bioluminescence originated as an environmental adaptation, ecological interaction has changed its role. Dinoflagellates can use bioluminescence as a defense mechanism. They can startle their predators by their flashing light, use it as an aposematic signal to warn of toxicity, or ward off potential predators by an indirect effect such as the "burglar alarm". In the "burglar alarm" hypothesis, bioluminescence attracts attention to the dinoflagellate and its attacker, making the predator more vulnerable to predation from higher trophic levels. This suggests that the copepod behavior is what causes the "burglar alarm" effect as opposed to the bioluminescence by itself. All of these hypotheses indicate that bioluminescence is advantageous for survival which is why it is a conserved trait among dinoflagellates. Bioluminescent dinoflagellate ecosystem bays are among the rarest and most fragile, with the most famous ones being the Bioluminescent Bay in
La Parguera, Lajas, Puerto Rico; Mosquito Bay in
Vieques, Puerto Rico; and Las Cabezas de San Juan Reserva Natural
Fajardo, Puerto Rico. Also, a bioluminescent lagoon is near Montego Bay, Jamaica, and bioluminescent harbors surround Castine, Maine. Within the United States, Central Florida is home to the
Indian River Lagoon which is abundant with dinoflagellates in the summer and bioluminescent ctenophore in the winter.
Lipid and sterol production Dinoflagellates produce characteristic lipids and sterols. One of these sterols is typical of dinoflagellates and is called
dinosterol.
Transport Dinoflagellate
theca can sink rapidly to the seafloor in
marine snow. ==Life cycle==