Mixotrophic dinoflagellate

Some dinoflagellates that live as parasites are probably mixotrophic. Karenia, Karlodinium, and Lepidodinium are some of the dinoflagellate genera which are thought to contain peridinin, a carotenoid pigment necessary for photosynthesis in dinoflagellates; however, chlorophyll b has been found in these genera as an accessory pigment. Certain species of mixotrophic dinoflagellates can be affected by light intensity and nutrient conditions . For example, ingestion rates of Fragilidium subglobosum, Gymnodinium gracilentum, and Karlodinium veneficum increase as light intensity increases up to 75 to 100 μmol photons per m2 per second. In contrast, other species are not affected by light intensity. == Types of feeding ==

Marine dinoflagellate species undergo three major trophic modes: autotrophy, mixotrophy and heterotrophy. Many species of dinoflagellates were previously assumed to be exclusively autotrophic; however, recent research has revealed that many dinoflagellates that were thought to be exclusively phototrophic are actually mixotrophic. == Implications for microbial food webs ==

Mixotroph dinoflagellates belonging to the species Gymnodinium sanguineum feed on nanociliate populations in Chesapeake Bay. Predation on ciliates is advantageous for G. sanguineum as the ciliates provide a source of nitrogen which is limiting to the growth of purely photosynthetic dinoflagellates. By preying on ciliates, these dinoflagellates reverse the normal flow of material from primary producer to consumer and influence the trophodynamics of the microbial food web in Chesapeake Bay Several established ecological models of marine microbial food webs have not included feeding by mixotrophic dinoflagellates. These additions would include feeding by mixotrophic dinoflagellates on bacteria, phytoplankton, other mixotrophic dinoflagellates and nanoflagellates, and heterotrophic protists. The impact of grazing by mixotrophic dinoflagellates will affect particular prey species and be influenced by the abundance of dinoflagellate predators and their ingestion rates. Another consideration would be to include predator-prey relationships of mixotrophic dinoflagellates at a species level due to co-existence in offshore and oceanic waters. The diversity of mixotrophic dinoflagellate species and their interactions with other marine organisms contributes to their diverse roles in different niche environments. For example, mixotrophic and heterotrophic dinoflagellates may act as predators on a wide range of prey types due to their diverse feeding mechanisms. Including mixotrophic dinoflagellates would better explain the control of prey population and cycling of limited materials as well as competition between other organisms for larger prey. == Climate change and ocean acidification ==

As CO2 concentrations in the atmosphere increase via anthropogenic causes, acidification of the ocean will increase as the result of increasing CO2 sequestration by the ocean; the ocean is a great sink for carbon, absorbing more as its concentration in the atmosphere increases. As this occurs, there will be species and community composition shifts in marine plankton communities. Mixotrophic dinoflagellates will be favoured over photosynthetic dinoflagellates, as the oceans will become more nutrient limited and mixotrophs will not have to rely only on inorganic nutrients but will be able to take advantage of being able to consume particulate organic matter. == Influence on red tide and HABs ==

Many mixotrophic and some heterotrophic dinoflagellates are known to cause red tides or harmful blooms that result in large-scale mortality of fish and shellfish. The very high levels of biomass in Red Tides or HABs can have direct toxic effects through the release of toxic compounds or indirect effects through oxygen depletion on mammals, fish, shellfish, and humans. The toxin concentrations can cause harmful and even deadly effects on humans and marine mammal populations that feed on contaminated shellfish. == Relationship to other organisms ==

Mixotrophic dinoflagellates can feed on various organisms including bacteria, picoeukaryotes, nanoflagellates, diatoms, protists, metazoans and other dinoflagellates, as well. Feeding and digestion rates in mixotrophic dinoflagellates are lower than those in strictly heterotrophic dinoflagellates. Mixotrophic dinoflagellates do not feed on blood, eggs, adult metazoans, and flesh, such as occurs in some heterotrophic dinoflagellates. == References ==