Protozoans, feeding

Although phototrophs are restricted to the surface ocean, photosynthesis is the ultimate source of almost all the organic matter that supports heterotrophic activity in the sea. As shown in Figure 8.1, this organic matter is transferred through the marine food web by the feeding activities of heterotrophs including bacteria, protozoans, and animals. 

Reports on copepods and other crustaceans dominate available zooplankton grazing data on Phaeocystis spp. These data show a wide range of rates, even for similar predator-prey combinations. We therefore attempt to summarize available quantitative data in relation to some of the mechanisms proposed to control the feeding on Phaeocystis. The shortage of quantitative feeding studies on microzooplankton and Phaeocystis was pointed out already a decade ago (Weisse et al. 1994), and the number of such studies is still limited, especially for protozoan microzooplankton, whether using laboratory cultures (Table 3)... 

Irigoien X, Titelman J, Harris RP, Harbour D, Castellani C (2003) Feeding of Calanusfinmarchicus nauplii in the Irm-inger Sea. Mar Ecol Prog Ser 262 193-200 Jakobsen HH, Tang KW (2002) Effects of protozoan grazing on colony formation in Phaeocystis globosa (Prymnesiophyceae) and the potential costs and benefits. Aquat Microb Ecol 27 261-227... 

Verity PG (1988) Chemosensory behavior in marine planktonic ciliates. Bull Mar Sci 43 772-782 Verity PG (1991) Feeding in planktonic protozoans evidence for non-random acquisition of prey. Mar Microb Food Webs 5 69-76... 

Giardia lamblia. Giardia lamblia is a flagellate parasitic protozoan. This parasite is largely confined to the lining of the intestine. It can colonize the lining and feed and grow there. It is shed in feces in the form of cysts. The cyst, however, cannot multiply outside the host. 

My final topic on in-feed agents is a major problem in the broiler industry. Coccidiosis is a protozoan disease of poultry caused by various Eimeria spp. It is highly prevalent in the intensive rearing conditions common in North America and Western Europe. In fact, such intensive rearing would not be possible without effective anticoccidials. 

Other types of parasitic protozoa infect the blood or tissues of their hosts. These protozoa are typically transmitted through another organism, called a vector, which carries the parasite before it enters the final host. Often the vector is an invertebrate, such as an insect, that itself feeds on the host and passes the protozoan on through the bite wound. Some of the most infamous of these protozoa are members of the genera Plasmodium, that cause malaria Trypanosoma, that cause African sleeping sickness and Leishmania, which leads to a number of debilitating and disfiguring diseases. 

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