Dinoflagellates

Superclass Dinoflagellata

Dinoflagellates are unicellular algae living in mostly marine environments, but freshwater representatives exist. Most are heterotrophic and parasitic, but others are photosynthetic. This latter group is known for forming a symbiotic relationship with non-motile marine animals, such as corals, anemones, and giant clams. These dinoflagellates (called zooxanthellae) live inside the tissues of these animals, providing sugars from photosynthesis. Coral bleaching is a phenomenon inwhich warming and acidifying oceans kill these colorful dinoflagellate symbionts, leaving the coral polyps looking gray or whitish. The loss of the symbiont can cause the coral host to die.

Some dinoflagellates are also known for having bioluminescence which can be seen at night in tropical waters. The agitation of water from waves and animals can make the water appear to glow.

Lastly, this group is known for creating red tides, which appear as a discoloration of coastal waters. These blooms of dinoflagellates are usually caused by an influx of nutrients, sometimes from pollution runoff. These blooms can produce harmful neurotoxins

Diversity

  • Mostly marine; 2,000 species; 425 genera

Classification

└SAR Supergroup

└Alveolates

└Dinoflagellates

Geologic Age

Ecology & form

  • Unicellular, aquatic organisms

  • They possess 2 flagella in grooves: 1 equatorial (around mid-section) and 1 apical (at the tip)

  • These algae have external plates called theca

  • Dinoflagellates can form cysts, when conditions become unfavorable

    • Dinoflagellates have permanently condensed chromosomes, which is distinctive among eukaryotes

    • Most are heterotrophic; parasites on fish or protists

    • Some are photosynthetic, using chlorophyll a and c, and peridinin pigments

    • Some do not have their own chloroplasts, but host a phototrophic endosymbiont, and a few may use alien chloroplasts (cleptochloroplasts), obtained from photosynthetic organisms they consumed (kleptoplasty)

Above: the dinoflagellate, Ceratium

Bioluminescence

  • At least 18 genera of dinoflagellates are able to produce bioluminescence (Haddock et al. 2010)

  • The algae glow when agitated by waves or swimming animals

  • Dinoflagellates may use bioluminescence for defense against invertebrate predators, shining when they detect a predator, possibly making the predator more vulnerable by attracting the attention of predators from higher trophic levels (Haddock et al. 2010)

Above: bioluminescence of algae in the water

Left: Dolphins swimming through waters with bioluminescent algae

Zooxanthellae

  • A symbiotic relationship between dinoflagellates and marine animals (e.g. anemones, corals, clams, etc.)

    • Non-flagellated dinoflagellates living inside animal cells

    • Dinoflagellates produce sugars through photosynthesis and share with the host animal

  • They provide their host with the organic carbon products of photosynthesis, sometimes providing up to 90% of their host's energy needs

  • In return, they receive nutrients, carbon dioxide, and an elevated position with access to sunshine

Above: The zooxanthellae dinoflagellates inside the polyps of coral

Above: The zooxanthellae dinoflagellate, Symbiodinium, commonly found in corals and anemones

Red tides

  • Cause of discoloration of water along tropical oceans

  • Some species produce neurotoxins, and the genus Alexandrium is the most numerous and widespread toxin producers

    • Paralytic shellfish poisoning is caused by eating affected shellfish, such as clams, mussels, and oysters

    • Humans can be affected by eating fish or shellfish containing the toxins; affects muscle function

Above: red tide caused by dinoflagellates