The "Paradox of the Plankton" or why are there so many co-existing species in a seemingly homogenous environment, has resisted explanation for decades. Planktonic microbes are not only diverse but are the base of the marine ecosystem. Phytoplankton are responsible for most of the primary production on earth and about 70 % is directly consumed by microzooplankton. Most planktonic protists, identified via morphological characteristics, appear to be widely distributed. However, cryptic species, genetically distinct but morphologically similar, have been described.
To examine these questions we will target 3 contrasting groups of protists, representatives of phytoplankton, microzooplankton and a group of intracellular parasites. We will focus on :
For the first two groups there is a great deal of biogeographic and ecological data. The third group appears to be exclusively parasites, notably of dinoflagellates and tintinnids. We will examine their morphological variablity, genetic structure and biochemical compositions.
For each group of organisms, the structure of populations will examined among individuals within a population through the characterization of single cells and between populations separated by different scales of time and space. Genetic work will begin with the use of rRNA and ITS data, but will also make use of house keeping genes. For the free-living forms morphometrics wil be used to characterise variability within a species and biochemical variabilty will be examined through analysis of structural lipids. Our aim is determine if apparently common species are able to exploit a wide variety of conditions or alternatively are in reality a suite of distinct forms.