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Species[edit | edit source]

Some dinoflagellates that live as parasites are probably mixotrophic. Karenia, Karlodinium, Lepidodinium are some of the dinoflagellate genera which were thought to contain peridinin, a carotenoid pigment necessary in phototrophic dinoflagellates. However, chlorophyll b was found in Karenia, Karlodinium, Lepidodinium as accessory pigments. This discovery has led scientists to assume that the pigment chlorophyll b actually came from preys which the mentioned dinoflagellates had taken in via feeding. Some mixotrophic dinoflagellate species are able to feed on toxic preys such as toxic algae and toxic organisms. Lingulodinium polyedrum and Akashiwo sanguinea, the two mixotrophic dinoflagellates, are known with the ability to feed on toxic dinoflagellate known as Alexandrium tamarense. Certain species of mixotrophic dinoflagellates can be affected by light intensity and nutrient conditions depending on dinoflagellate species. Ingestion rates of Fragilidium subglobosum, Gymnodinium gracilentum, and Karlodinium veneficum increase as light intensity increases up to 75-100 µE m-2 s -1. Some species are not affected by light intensity. Ceratium Furca’s , a mixotrophic dinoflagellate, ingestion rate was discovered to be affected by intracellular nutrient concentrations.

Types of feeding[edit | edit source]

Marine dinoflagellate species undergo three major trophic modes: autotrophy, mixotrophy and heterotrophy. Many species were previously assumed to be exclusively autotrophic dinoflagellates, however recent research has revealed that many phototrophic dinoflagellates are actually mixotrophic dinoflagellates. Mixotrophic dinoflagellates can undergo both photosynthesis and phagocytosis as a method of feeding. Mixotrophic dinoflagellates with individual plastids that depend mostly on photosynthesis can prey on other cells as their secondary source of nutrients. On the other hand, mixotrophic dinoflagellates with individual plastids that depend mainly on phagocytosis are also photosynthetic due to kleptochloroplasts or algal endosymbionts. The importance of uptaking nutrients from various methods including photosynthesis and inorganic nutrients are yet to be found. Dinoflagellates were thought to only have one mouth as a path of food intake. It was discovered that Gonyaulax polygramma and Scrippsiella spp., mixotrophic dinoflagellates, can engulf prey with small size via their apical horn while larger preys will be engulfed via their sulcus, proving that dinoflagellates have more than one mouth used in feeding. Karlodinium armiger, a mixotrophic dinoflagellate, can feed using two different mechanisms including direct engulfment on small preys and peduncle feeding on larger preys.

Influence on microbial food web[edit | edit source]

Mixotrophic dinoflagellate Gymnodinium sanguineum feed on nanociliate populations in Chesapeake Bay using the gut clearance/gut fullness approach. Predation on ciliates is advantageous for G. sanguineum as the ciliates provide nitrogen as a source of nutrient compared to purely photosynthetic dinoflagellates in nitrogen limited environments. By preying on ciliates, these dinoflagellates reverse the normal flow of material from primary producer to consumer and influence trophodynamics of the microbial food web in Chesapeake Bay.

Several ecological models of marine microbial food webs established 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. Grazing impact on a particular prey species is influenced by abundance of dinoflagellate predators and ingestion rates of the predator. 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 dinoflagellates species and their interactions with other marine organisms contributes to their diverse roles in different niche environments. Mixotrophic and heterotrophic dinoflagellates may act as predators on diverse types of prey 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.

Influence on red tide[edit | edit source]

Many mixotrophic and some heterotrophic dinoflagellates have been known to cause red tides or harmful blooms that result in large-scale mortality of fish and shellfish. Studies on red tides have been conducted to determine the mechanism of outbreak and the persistence of red tide caused by mixotrophic dinoflagellates such as Karenia brevis, P. donghainese and P. minimum in low nutrient concentration waters. In the case of serial red tides, one mixotrophic dinoflagellate species is dominated by another mixotrophic species in rapid succession over a short span of days. A possible explanation to the occurrence of different dominant mixotrophic dinoflagellates during serial red tides is the ability of mixotrophic dinoflagellates to feed on both heterotrophic bacteria and cyanobacteria (such as Synecchococcus), which provide limiting nutrients such as phosphorus, and nitrogen simultaneously. It is proposed that during serial red tides, feeding by larger mixotrophic dinoflagellates on smaller species may be a driving force for the succession of dominant species. Nitrogen and phosphorus is taken up by direct transfer of the materials and energy between the mixotrophic dinoflagellates and therefore may not rely on uptake and release of nitrogen and phosphorus by other organisms which can cause uncoupling between nutrient concentrations and the abundance of mixotrophic dinoflagellates in natural environments.

Relationship to other organisms[edit | edit source]

Mixotrophic dinoflagellates can feed on various sources including bacteria, picoeukaryotes, nanoflagellates, diatoms, protists, metazoans and dinoflagellates themselves as well. Feeding and digestion in mixotrophic dinoflagellates are lower than those in heterotrophic dinoflagellates. Mixotrophic dinoflagellates do not feed on blood, eggs, adult metazoans, flesh like heterotrophic dinoflagellates do.