Colomban de Vargas, Rutgers University, USA
Luc Beaufort, CNRS, CEREGE
Assessment of the morphological, genetic, and ecological
diversity of coccolithophores along the BIOSOPE transect.
Overarching Goal:
The Prymnesiophyceae are the most abundant organisms of the nannoplankton
(2-20 μm) in the oligotrophic ocean, where they play a key role in directing flows
of biogeochemically and climatically major elements and gasses.
Coccolithophores, (Prymnesiophyceae) are one of the rare phytoplanktonic
group to produce calcite (40 to 50% of global CaCO3 production)
We propose
1 - to examine, using innovative methods in molecular biology and
microscopy, the genetic and morphological diversity of coccolithophores along the
vertical and horizontal ecological gradients covered during the BIOSOPE cruise.
2- to quantify calcite production by coccolithophores along the BIOSOPE
transect in order to establish relation between organic production and calcite
production at specific level.
Scientific Objectives:
To estimate the coccolithophore diversity (taxonomy, abundance) at the
species level in both the depth and biogeographic ecological gradients
covered by BIOSOPE.
To identify the genetic provinces of the key coccolithophore taxa in the stratified
oligotrophic ocean, and compare the ecological partitioning between the
morphological and genetic diversity.
To estimate the coccolithophore CaCO3 production in the biogeographic areas
covered by BIOSOPE, and particularly in extreme oligotrophic environments.
To estimate the ecological importance of naked coccolithophores and other
haptophytes in extreme oligotrophy.
To analyze the global diversity of nannoplanktonic eukaryotes along BIOSOPE
Methods
All proposed methods are based on materiel collected on different kind
of filters :
The morphological diversity of coccolithophores will be analyzed using:
SYRACO: the “SYsteme de Reconnaissance Automatique de COccolithes”, which will allow a rapid
–1000 individuals per minute- screening of (1) the morphological taxonomy, (2) the abundance of
morphological species at each station and depths, (3) the weight of individual coccoliths and thus
the production of CaCO3.
Scanning Electron Microscopy: SEM will allow the recognition of ultrastructural characters of the
skeleton that allow species distinction in the biological, genetically defined species of
coccolithophore.
The genetic diversity of coccolithophores will be analyzed using:
DNA PCR, sequencing, RFLP: The use of specific DNA primers targetting different taxonomic
levels within the coccolithophores will allow to (1) reconstruct a first, global phylogeny of the tropical
coccolithophores, (2) detect the cryptic genetic diversity within the classical, morphological
“species”, (3) analyse the biogeographic and depth partitioning of genetic diversity within the most
important taxa.
Fluorescence In Situ Hybridization : FISH will permit the identification of naked or non-calcifying
coccolithophores and other haptophytes.
SSU rDNA clones librairies : rDNA librairies will allow a rapid survey of the nannoplanktonic
diversity present along BIOSOPE.
Dollfus & Beauffort, Neur. Net., 1999
Beaufort & Dollfus, Mar. Mic. In Press
E. huxleyi
U. tenuis
CaCO3, growth rate, PP
Stoll et al., 2002
Sampling Strategy
We propose to examine 6 different depths at each station:
2 samples below the Deep Chlorophyll Maximum (DCM)
1 in the DCM
1 just above the DCM
For each depth, we will need 12 liters of sea water
1 in the midle-photic zone
to accommodate the following protocol:
1 in the upper-photic zone
12 liters
8l
Polycarbonate
Membrane
0.8 μm
2-4 l
1l
FISH
SEM
Genetics
Cellulose
acetate
membrane
SYRACO