Part F | 33.3
792 Part F Marine Derived Metabolites
33.3 Marine Dinoflagellates
The latest estimates suggest a total of 2294 living
dinoflagellate species, which include marine, freshwater, and parasitic dinoflagellates [33.27]. Of the
2000 living species, more than 1700 are marine and
about 220 are from freshwater [33.28]. Among them
extant species have been described, approximately
only half of which are photosynthetic. They include
autotrophs, mixotrophs, and grazers. These species
possess chloroplasts with chlorophyll a and c pigments. Other species are heterotrophic and can absorb small particles or other cells. The other pigments they contain are carotenes and various xanthines, including peridinin, a unique xanthine pigment
specific to this group of organisms. Photosynthesizing dinoflagellates accumulate starch as a food reserve. The remaining obligate heterotrophs can have
a diverse range of nutritional lifestyles, including
saprophytic, parasitic, phagotrophic, or carnivorous
forms [33.27, 28]. This dual animal–plant behavior
within the group has led to their being classified under both the zoological and botanical nomenclature,
but they are now generally classified under botanical rules. They can have complex life cycles but, for
most species, the major life stage is a free-living flagellated form. They form an important component of
aquatic phytoplankton, but there are also many benthic
species [33.29].
Several aspects of the behavior, physiology, and
ecology of dinoflagellates are notable and can be highlighted, such as: swimming behavior, bioluminescence,
heterotrophy, symbiosis, and toxicity.
33.3.1 Swimming Behavior
Free-living dinoflagellates live in most wet environments, but in the open ocean they are extremely numerous, especially in more tropical waters and when
concentrations of nutrients are high. As motile cells,
dinoflagellates are capable of directed swimming behavior in response to a variety of parameters. These
include chemotaxis, phototaxis, and geotaxis, for which
movement is controlled by chemical stimuli, light, or
gravity, respectively. It has long been observed that
many dinoflagellates do not move randomly through the
water column but instead aggregate at specific depths
that can vary with the time of day. This vertical migration has proven to be a highly complex process that
varies between species and with environmental or nutritional conditions [33.30].
33.3.2 Heterotrophy
About half of the extant dinoflagellates lack a plastid or pigments to carry out photosynthesis [33.31].
Most naked heterotrophic dinoflagellates have flexible cell walls that allow them to engulf living cells
and particles (phagotrophy), which can then be seen
inside the colorless dinoflagellate. The phagotrophic dinoflagellate Gyrodinium fusus has been shown to be
an important grazer of Azadinium cf. spinosum during the first bloom, suggesting that its grazing activity
could have acted as a modeling factor in population levels of its prey. There are also many parasitic forms,
but in most cases they are very difficult to recognize
as dinoflagellates. Some species will parasitize other
organisms, such as zooplankton and other protists, filamentous algae, or fish. Roughly 5% are parasitic on
aquatic organisms.
33.3.3 Symbiosis
Some dinoflagellates (zooxanthellae) are capable of
forming symbioses with a phylogenetically wide range
of marine protists and invertebrate animals. Energy generated by zooxanthellae through photosynthesis is taken
up by the host (a reef coral). The energy from the
zooxanthellae can amount to more than the daily requirement of the host. It is thought that the evolution of
the association between dinoflagellates and corals may
have been instrumental in the development of the coral
reef ecosystem and might be essential for its maintenance. Within the dinoflagellate lineage, at least seven
genera from four orders are found in symbiotic associations [33.32]. The hosts in dinoflagellate associations
with other organisms include foraminifera, radiolarians, flatworms, anemones, jellyfish, and even bivalve
mollusks. Some dinoflagellates may themselves possess
endosymbionts.
33.3.4 Bioluminescence
The spectacular display of blue sparkling light seen as
waves break on beaches or as a boat passes through the
water in the night is called bioluminescence. The Dinoflagellata are sometimes called Pyrrophyta, meaning
fire plants. This is because some species are capable
of bioluminescence, in which chemicals made by the
organism produce light in a chemical reaction. The
phenomenon was first noted in the genus Noctiluca,
792 Part F Marine Derived Metabolites
33.3 Marine Dinoflagellates
The latest estimates suggest a total of 2294 living
dinoflagellate species, which include marine, freshwater, and parasitic dinoflagellates [33.27]. Of the
2000 living species, more than 1700 are marine and
about 220 are from freshwater [33.28]. Among them
extant species have been described, approximately
only half of which are photosynthetic. They include
autotrophs, mixotrophs, and grazers. These species
possess chloroplasts with chlorophyll a and c pigments. Other species are heterotrophic and can absorb small particles or other cells. The other pigments they contain are carotenes and various xanthines, including peridinin, a unique xanthine pigment
specific to this group of organisms. Photosynthesizing dinoflagellates accumulate starch as a food reserve. The remaining obligate heterotrophs can have
a diverse range of nutritional lifestyles, including
saprophytic, parasitic, phagotrophic, or carnivorous
forms [33.27, 28]. This dual animal–plant behavior
within the group has led to their being classified under both the zoological and botanical nomenclature,
but they are now generally classified under botanical rules. They can have complex life cycles but, for
most species, the major life stage is a free-living flagellated form. They form an important component of
aquatic phytoplankton, but there are also many benthic
species [33.29].
Several aspects of the behavior, physiology, and
ecology of dinoflagellates are notable and can be highlighted, such as: swimming behavior, bioluminescence,
heterotrophy, symbiosis, and toxicity.
33.3.1 Swimming Behavior
Free-living dinoflagellates live in most wet environments, but in the open ocean they are extremely numerous, especially in more tropical waters and when
concentrations of nutrients are high. As motile cells,
dinoflagellates are capable of directed swimming behavior in response to a variety of parameters. These
include chemotaxis, phototaxis, and geotaxis, for which
movement is controlled by chemical stimuli, light, or
gravity, respectively. It has long been observed that
many dinoflagellates do not move randomly through the
water column but instead aggregate at specific depths
that can vary with the time of day. This vertical migration has proven to be a highly complex process that
varies between species and with environmental or nutritional conditions [33.30].
33.3.2 Heterotrophy
About half of the extant dinoflagellates lack a plastid or pigments to carry out photosynthesis [33.31].
Most naked heterotrophic dinoflagellates have flexible cell walls that allow them to engulf living cells
and particles (phagotrophy), which can then be seen
inside the colorless dinoflagellate. The phagotrophic dinoflagellate Gyrodinium fusus has been shown to be
an important grazer of Azadinium cf. spinosum during the first bloom, suggesting that its grazing activity
could have acted as a modeling factor in population levels of its prey. There are also many parasitic forms,
but in most cases they are very difficult to recognize
as dinoflagellates. Some species will parasitize other
organisms, such as zooplankton and other protists, filamentous algae, or fish. Roughly 5% are parasitic on
aquatic organisms.
33.3.3 Symbiosis
Some dinoflagellates (zooxanthellae) are capable of
forming symbioses with a phylogenetically wide range
of marine protists and invertebrate animals. Energy generated by zooxanthellae through photosynthesis is taken
up by the host (a reef coral). The energy from the
zooxanthellae can amount to more than the daily requirement of the host. It is thought that the evolution of
the association between dinoflagellates and corals may
have been instrumental in the development of the coral
reef ecosystem and might be essential for its maintenance. Within the dinoflagellate lineage, at least seven
genera from four orders are found in symbiotic associations [33.32]. The hosts in dinoflagellate associations
with other organisms include foraminifera, radiolarians, flatworms, anemones, jellyfish, and even bivalve
mollusks. Some dinoflagellates may themselves possess
endosymbionts.
33.3.4 Bioluminescence
The spectacular display of blue sparkling light seen as
waves break on beaches or as a boat passes through the
water in the night is called bioluminescence. The Dinoflagellata are sometimes called Pyrrophyta, meaning
fire plants. This is because some species are capable
of bioluminescence, in which chemicals made by the
organism produce light in a chemical reaction. The
phenomenon was first noted in the genus Noctiluca,