|
Context
It
is now well recognized that in the intertropical area of the
central and west Pacific Ocean, picoplankton dominates
phytoplankton biomass (Peña et al., 1990;
Le Bouteiller and
Blanchot, 1991; Le Bouteiller et al.,
1992) In the open ocean, Prochlorococcus
account for the majority of the biomass and productivity (Blanchot and Rodier,
1996; Landry et al., 1996, Campbell et al.,
1987). In coral reef environments, the dominance of Synechococcus
was first recorded using epifluorescent microscopy (Blanchot et
al., 1989), which was later confirmed by flow cytometry (Charpy
and Blanchot, 1996) A recent paper from Charpy and Blanchot (1998)
show that in eleven French Polynesian atoll lagoons, Synechococcus
formed the predominant group in terms of abundance, carbon biomass
and primary production in most lagoons. However, average lagoonal
picoplankton abundance varied by a factor of 200 depending on the
geomorphology of the atolls. In other coral reef area, the Great
Astrolabe (Fiji), Synechococcus
largely dominated the picoplankton biomass (91 %) and
contributed to 42 % of total phytoplankton biomass.
Scientific
Strategy
|
F
Are picocyanobacteria dominant in all the inter-tropical area?
F
Why does the taxonomic composition of cyanobacteria in atolls change
dramatically from coastal waters dominated by Synechococcus to open ocean dominated by Prochlorococcus?
F
Are picocyanobacteria able to fix molecular nitrogen?
F
What are the causes of cyanobacteria blooms and their consequences on
coastal ecosystem?
F
What is the role of cyanobacteria in aquaculture ponds?
|
Ecological
studies
In order to assess the environmental factors
responsible for the dominance of cyanobacteria, we choose study
sites presenting the gradients of factor presented below:
The
chosen sites are:
Pacific Ocean
Ø
Mooréa
lagoon (French Polynesia): A very well studied high island lagoon
Ø
Takapoto
atoll (French Polynesia): Probably the most studied atoll lagoon
Indian Ocean
Ø
La
Réunion: Area of the Marine park
Ø
Mayotte:
This lagoon is studied since 1983 by the COM team which is partner.
Ø
Madagascar:
The area of Toliari is studied since 1961.
Atlantic Ocean
Batabano
Gulf (Cuba) is separated from the ocean by a coral reef barrier.
It is an area of high interest due to the importance of lobster
fishery and the presence of a coastal upwelling, which enrich
periodically the shallow waters of the gulf.
|
Ø
N2
fixation (Acetylene and 15N2)
Ø
15N,
13C, 14C uptake
Ø
33P
uptake and regeneration
Ø
Bio-assays
(+Fe, +P)
Ø
DOM
excretion (DMOD,
15N, 13C)
Ø
Grazing
Ø
POM
sedimentation rate |
Ø
Research
of the presence of the nif
gene in marine picocyanobacteria by PCR
Ø
Cloning
and sequencing of the nif
gene
Ø
Use
of molecular tools for genetic identification of cyanobacteria:
characterization with 16S rRNA
Two
models will be developed:
Ø
An
ecosystem model focused on primary productivity, built from the
existing database of the well-studied atoll of Takapoto. Specific
algorithms of cyanobacteria compartment will be tested on this
model.
Ø
A
process model focused on nitrogen fixation in order to improve the
determinism of the ecosystem model.
|
Home
