Picoplankton (defined operationally as cells that pass through a 3 micron filter) dominate the photosynthetic biomass in many marine ecosystems, not only in the very oligotrophic regions of the world oceans, such as the Eastern Mediterranean Sea, but also in mesotrophic areas. However, picophytoplankton are clearly not exclusively restricted to pelagic environments. In many coastal regions, they are present throughout the year and constitute a 'background' population, onto which episodic phenomena such as the spring bloom develops. In some environments, such as coastal lagoons, picoplankton can be a major component of biomass and productivity for most of the year. In addition, some bloom-forming picoplankters such as Aureococcus spp. are toxic. However, to date fewer than 30 species of picophytoplankton have been described. A clear proof of our poor knowledge of picophytoplankton diversity is revealed by the discovery of three novel algal classes in the last ten years described from picophytoplanktonic taxa.
Because so little is known about the taxonomy and systematics of picophytoplankton we have very little data to estimate the levels of its biodiversity under natural conditions and how picophytoplankton are affected by environmental variability linked to either anthropogenic influence or to larger scale phenomena such as those linked to climate change or global warming.
The major objective of this project is to develop, test and validate probing methods based on molecular biology techniques that allow for routine and extensive assessment of picophytoplankton diversity (species composition and relative contribution of taxa to total community) in the marine environment.
Our strategy to meet this objective is encapsulated in the following four steps:
(1) Obtain SSU rDNA sequences for as many as possible picophytoplankton taxa from both cultures and natural samples. Novel taxa will be assessed using a combination of methods including in particular pigment analysis and electron microscopy.
(2) Using this sequence database, develop hierarchical probes recognizing each taxonomic group having picophytoplanktonic representatives
(3) Develop fast and efficient techniques to quantify the fraction of the pico-phytoplankton recognized by the probes in natural samples.
4) Test and validate these probes on time series of picophytoplankton biodiversity in three coastal ecosystems.
The expected impacts of our project fall into four categories.
Understanding marine systems. Picophytoplankton forms the base of the food web in most marine systems. The large scale picture that will result from our project should lead to the identification and isolation of some of the key organisms in this size class. Future studies could then focus on these taxa to understand their physiology, their genetic diversity, their population dynamics and more generally their exact role in the ecosystem.
Monitoring marine systems. The tools and methods we intend to develop and validate will offer near real-time capabilities to monitor key biological components of marine systems because they rely on very recent developments in molecular biology such as the DNA chips or large scale gene sequencing. It is obvious that by the end of the project, better, faster, and less expensive instruments and technologies will be available to take advantage of the probes we will have developed.
Biotechnology. Although still used on a very small scale, microalgae are clearly an excellent material for many future biotechnology applications. Among microalgae, the smaller size classes constituted by picophytoplankton are potentially very attractive targets for several reasons such as the existence of many new phyla not yet investigated or their ease of culture.
Research in biology. Picoplankton offer many fascinating aspects that could be targeted in the future for fundamental studies in many fields of biology. As an example, their very small cell and genome sizes raise the question of how they evolve to function in a somewhat complex and changing environment with the smallest possible number of genes.