Dirty Tricks in the Plankton: Diversity and Role of Marine Parasitic Protists

Parasitism is an immensely successful mode of nutrition and parasitic organisms are abundant in most ecosystems. This is also the case for marine planktonic ecosystems in which a large variety of parasitic species are known. Most of these parasites are protists and they infect a wide range of hosts from the marine plankton, ranging from other protists to larger planktonic invertebrates. Parasites often have morphologies and life cycles that are highly specialized as compared to their free-living relatives. However, this does not mean that parasites are necessarily odd or rare phenomena; on the contrary parasites constitute numerically and ecologically important components of the ecosystem. This review gives an overview of the existing knowledge on the diversity and occurrence of parasitic protists in the marine plankton and examines the available information on the potential effects and role of parasitism in this ecosystem. Importance is given to the fact that prevalence and impact of parasitic organisms in marine planktonic systems appear to be overwhelmingly understudied

Observation of live specimens of Pseudotontonia cornuta (Ciliophora: Oligotrichida) reveals new distinctive characters

4 pages, 3 figures, 1 tableA large planktonic ciliate, Pseudotontonia cornuta, was observed during a cruise in the North Sea, Denmark, in summer 2001. Live cells as well as fixed and protargol-stained specimens were studied. The species possessed the characteristic tail of Tontoniidae, somatic ciliature classifying it as a Pseudotontonia, and cell proportions and oral ciliature corresponding to P. cornuta. Observation of live cells, however, revealed distinctive features as chloroplast-containing tentacles emerging just below the apical membranelles and an S-shaped proximal rim of the left margin of the oral cavity. These characters are eye-catching in live specimens, but have passed unnoticed till now because all previous studies on P. cornuta have been made on fixed samplesThis work was funded by the European Commission (Research Directorate General-Environment Programme-Marine Ecosystems) through the project BIOHAB (Biological Control of Harmful Algal Blooms in European coastal waters: role of eutrophication), contract EVK3-CT99-00015. BIOHAB is part of the EC EUROHAB clusterPeer Reviewe

Infection with the dinoflagellate parasite Blastodinium spp. in two Mediterranean copepods

9 pages, 7 figures, 1 tableInfection with the intestinal parasite Blastodinium mangini resulted in reduced survival of starved adults of the Mediterranean copepod Oncaea sp. No such effect was measurable for Corycaeus sp. infected by Blastodinium navicula. Both sexes of Oncaea sp. adults were infected by B. mangini and infected copepods were able to mate successfully. However, Oncaea sp. females infected by B. mangini did not produce eggs and, thus, appeared to be sterile. By inducing sterility, the harmful effect of B. mangini infection on Oncaea sp. populations is bound to be more profound than the effect on the individual level. The mechanism of infection by Blastodinium spp. remains unknown, but uptake of parasite zoospores by Oncaea sp. copepodites concurs with the hypothesis that infection occurs through the ingestion of zoospores by juvenile hostsThis work was financed by the European Commission, Directorate General Research, through a Marie Curie Postdoctoral fellowship (contract no. HPMF-CT-2002-01931)Peer Reviewe