The plankton behind glowing waves and red tides spins as it swims
Named for their whirling swim, dinoflagellates are single cells that can make the sea sparkle blue-green at night or turn it red with toxic blooms. Some live inside corals, some hunt other microbes, some do both photosynthesis and predation, and their chromosomes are packaged unlike those of almost any other complex cell.
The name joins the Greek for whirling with the Latin for whip. Each cell carries two different flagella: a ribbon-like one wrapped around its middle that beats sideways, and a trailing one that pushes backward, together driving the cell forward while spinning it. Many species wear armour of overlapping cellulose plates set in membrane sacs called alveoli, a structure linking them to ciliates and to the parasites known as Apicomplexa. Some unarmoured forms instead hold tiny star-shaped silica skeletons of unknown purpose.
Estimates of living species cluster around 2,000 to 2,300, most of them marine but roughly 220 in fresh water, and they turn up even in snow, ice and seabed sediments. Many photosynthesise, yet a large share are mixotrophs that also engulf prey. Their chloroplasts came from swallowed red algae in most lineages, but some borrowed plastids from green algae or even from captured diatoms. Species living inside marine animals are vital partners in coral reefs, while others are parasites of fish.
Their nucleus is a puzzle. In the core group, chromosomes stay condensed and fastened to the nuclear membrane, with few or none of the histone proteins that normally package eukaryotic DNA. Some species produce dormant cysts, and their ability to switch between cyst-forming and non-cyst strategies makes reconstructing their evolution very difficult.
People noticed them early. In 1753 Henry Baker described the tiny animals that make seawater sparkle, now known as Noctiluca, and in the 1830s Christian Gottfried Ehrenberg named genera still used today. Botanists once called the group fire algae after its glowing members. Dense blooms can colour water as red tides, and eating shellfish from affected waters can poison people. One species, Pfiesteria piscicida, meaning fish-killer, has been blamed by some researchers for harmful blooms off North Carolina and Maryland in the 1980s and 1990s.
Source: Dinoflagellate
