Protist functional stability in pico-nanoplanktonic marine coastal communities.
Ramond P., Sourisseau M., Audic S., Simon N., Romac S., Schimtt S., Rigaut-Jalabert F., de Vargas C., Siano R.,
KW: Molecular Ecology, Functional Diversity, Biological Traits, Coastal Ecosystems, Community Structure
Seeking for general patterns of protist community structuring in the marine coastal ecosystem, we tried to synthesise the genetic diversity of marine planktonic protists by a functional diversity approach. We sampled pico-, nano-, and micro-plankton communities in marine coastal ecosystems submitted to different physical forcings, at different spatial and time scales. By means of a metabacording approach based on the high-throughput sequencing of the V4 domain of the 18S rDNA, we identified and taxonomically annotated 111.089 Operational Taxonomic Units (OTUs). We established a conceptual framework of 30 protist biological traits which reflect the variety of morphological forms, trophic strategies, and mode of life of both autotrophic and heterotrophic protists. A rigorous bibliographical work allowed annotating 13 out of 30 traits to at least half of our taxonomically annotated OTUs. Despite an evident lack of knowledge of protist biological traits, a combination of multivariate and clustering statistics allowed the identification of trade-off between well-annotated traits and the establishment of 6 distinct functional groups. The relative abundance of these functional groups was compared to genetic diversity. Their distribution across typical planktonic size-fractions (micro-, nano- and pico-plankton) was also studied. Functional groups distribution was less variable in the smallest planktonic size fractions, where the 6 functional groups showed comparable contributions across sample groups. Taking into account the whole biological diversity of marine protists, this study proposes new developments in the field of protist functional ecology, which was so far assessed only for the photoautotrophic compartment. It suggests that the functional and the genetic diversity of the coastal protist communities co-vary, and that the pico-nano-plankton is more stable than the micro-plankton both from a functional and genetic diversity perspective.