Paradox of Plankton

© John Dolan
Petalotricha ampulla with cilia extended

Planktonic microbes constitute the base of aquatic ecosystems. Protists are typical of the plankton as species richness seems unreasonably high—the "Paradox." In addition, each species appears widely distributed. Recent molecular data suggest that many protist species, defined morphologically, may be genetically diverse. Thus, many "species" of planktonic protists actually may be groups of cryptic species (morphologically indistinguishable, genetically divergent) each adapted to precise ecological niches. Conversely, many species have been catalogued which might be simply variants of a single species.

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In the Aquaparadox project, we examined morphological, genetic, and physiological diversity in a wide range of common coastal protist morpho-species—that is, morphologically defined species. The population structure of protist species was examined at the level of single cells and between populations separated by different scales of time and space. Genetic diversity was also evaluated. Morphometrics was used to characterise variability within a species and physiological adaptation using cultures. We also examined patterns of community assembly and historical trends in species distributions. Our goal was to provide a basis for understanding protist adaptation, speciation, and ecology in aquatic systems. For more information, click here

John Dolan is a marine biologist at CNRS, University Paris VI, Villefranche-sur-Mer, France. His research subjects are organisms of the microzooplankton, the microscopic herbivores which are the first link in the aquatic food chain. He has worked in lakes, estuaries, and a variety of marine systems ranging from tropical lagoons to Anarctica. His speciality is ciliate microzooplankton. In recent years, he has focused on the biodiversity of these organisms attempting to answer apparently simple question like: Why are there so many species of microzooplankton (there can be dozens in a liter of seawater)? Is each species doing a different thing?

Salad Bowl Diatom
Rhabdonella amor
Tintinnopsis campanula
Petalotricha ampulla with cilia extended
Wagon Wheel Diatom
Lithoptera mulleri (an Acantharian Radiolarian)
Stenosomella nivalis
Carpocanium sp. from the Aegean Sea
Pyrocystis lunula
King Radiolarian

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