Impact of the pCO2 level on microalgae' Comparison of past,present and future situations during meso

1
Impact of the pCO2 level on microalgae.Comparison
of past,present and future situations during
mesocosms experiments I-Phytoplanctonic
development and carbon standing
stockMartin-Jézéquel V1., Huonnic P 1,2.,Dubois
S1, Delille B3., Riebesell U4.1-Laboratoire de
Biologie Marine, EA2663, Université de Nantes, 2
rue de la Houssinière, BP 92208, F-44322,
France.2-UMR 6539, Université de Brest,
IUEM,Technopole Brest Iroise, F-29280, Plouzané,
France.3-Unité dOcéanographie Chimique,
Université de Liège, 17 Allée du 6 Aout, 4000,
Liège, Belgium4-Marine Biogeochemistry,
Institute for Marine Research, University of
Kiel, Duesternbrooker Weg 20, D-24105, Kiel,
Germany
INTRODUCTION Increase in anthropogenic CO2
transferred into the oceans in one of the main
features which will regulate the equilibrium of
oceanic systems in the futur.The increase in
atmospheric CO2 since the early 1900 has changed
oceanic pH by 0.1 units. It has been estimated
that the pH of seawater will decrease by 0.35
units by 2100, leading to a large increase of
pCO2 level in waters for the future. The impact
of these changes were investigated during a
multiparametric mesocosm experiment, conducted in
Norvegian coastal waters in May 2003 (Riebesell
et al, in prep).The pCO2 levels of the system
were adjusted to concentration anticipated for
next century (future) , the present day and
pre-industrial (past) situations. We report on
this poster results on the taxonomical
composition and on the adaptation of the
phytoplanctonic community.
Fig.4-Carbon biomass-M7
Fig.7-Carbon biomass-M7
Fig.1-Distribution of taxa in M7
METHODS The study was conducted in 8 mesocosms
filled with coastal waters, with 3 pCO2 levels
corresponding to future situation M1 to M3
present situation M4 to M6 and past situation
M7 and M8 . Samples of phytoplankton were
collected each day, fixed with lugol and cells
counts were made using the method of Uthermöhl
(1958). Cell size were measured under microscope,
and cell volume were calculated using the
equations of Hillebrand et al. (1999). For the
diatoms and dinoflagellates, the carbon content
of each cell was quantified using the equations
of Menden-Deuer et al. (2000). Mean values of
the litterature were used as cellular carbon for
Cryptophyceae (Montagnes et al, 1994),
undetermined nanoplancton (Moal et al, 1988) and
Cocolithophorids (Montagnes et al, 1994).
Statistical analysis were performed using data
of a 2-day frequency sampling in the 8 mesocosms,
using cellular abundance or carbon stock of the
whole taxa dataset and on subsets of the fauna,
as outlined in the result section. Multivariate
analysis followed methods of Clarke and Warwick
(1994) using the PRIMER software package. Data
analysis was performed by using non-metric
multidimensional scaling ordination (MDS) and
clusters were created using group average linking
with the Bray-Curtis similarity measure
(log-transformed data). ANOSIM (Analysis of
Similatity) was used to determine whether there
was a difference in community composition between
pCO2 condition (A future B present C past)
and/or evolution in time
Fig.5-Carbon biomass-M4
Fig.8-Carbon biomass-M4
Fig.2-Distribution of taxa in M4
Fig.3-Distribution of taxa in M1
Fig.6-Carbon biomass-M1
Fig.9-Carbon biomass-M1
RESULTS Cellular abundance on taxa level is shown
in figures 1, 2 and 3, for one mesocosm
characteristic of each pCO2 conditions ( past M7,
present M4 future M1). Large differences were
observed for each situation present waters
were dominated by coccolithophorids, whereas the
cells number of diatoms and coccolithophorids
were equivalent in past waters , and diatoms
competed with coccolithophorids in future
waters at the end of the experiment. The
maximal carbon stock sampled during the blooms
was quite similar for the three conditions, close
to 200 mg C/m3 (Figures 4,5,6). However, the
primary producer of this maximum of biomass could
differ from the dominant taxa determined by the
cell counts . In the past waters the main part
of the carbon stock was provided by diatoms, and
in the future waters diatoms have produced more
carbon than coccolithophorids at the end of the
experiment. The respective contribution of
diatoms and coccolithophorids in cellular
concentration or carbon biomass has remained the
same only in the present waters. Details on the
distribution of the carbon biomass of the 11
families of diatoms and the 3 families of
dinoflagellates are shown in figures 7, 8 and 9.
Bacillariaceae have contributed for the major
part of the stock in present and past waters,
and Fragilariaceae in future waters. For the
three conditions, the carbon produced by the
Gymnodiniaceae was always relatively high. Other
families such as Thalassiosiraceae, Naviculaceae
or Ceratiaceae have participated for a minor part
in the total biomass. The classification of the
communities (Bray-Curtis similarity) was obtained
for the cellular abundance ( Figure 10 MDS,
figure 11 CLUSTER), and for the carbon stock
(Figure 12 MDS, figure13 CLUSTER).The
families of diatoms and dinoflagellates are
classified in figure 14 on their cellular
abundance (only MDS is shown), and the taxa are
analyzed on their carbon stock in figure 15 (
only MDS is shown). All these results show that a
significant distinction of the phytoplanktonic
assemblages can be made between the waters of
past (C), present (B) and future (A), and
that the differences between the three conditions
are statistically higher when the description of
the system includes the phytoplanctonic families
than when taxa alone are used. The populations
grown under the future conditions are clearly
discriminated in the analysis of the communities
(Label A clusters Figures 11 13). ANOSIM with
pCO2 conditions tested on the matrix of whole
communities or on families of diatoms and
dinoflagellates are highly significant
(plt0.001).The structure of the communities is
illustrated by k-dominance curves based on cell
concentration (Figures 16 18) and carbon
biomass (Figures 17 19).The communities
described by cellular abundance of all taxa are
not well structured especially in the present
waters (Figure 16). The communities described by
diatoms and dinoflagellates are well structured
and the assemblage remained more stable in the
present than in the past and future waters
(Figure 18 19). Positions of families and taxa
during the study were also analysed with the
Bray-Curtis similarity-test. Significant
assemblages can be described in figures 20 21
1) Baccillariaceae Fragilariaceae
(microplankton) 2)Gymnodiniaceae, Cryptophyceae
undetermined nanoplancton Coccolithophorids
(nannoplankton). These two assemblages have
formed the basis of the phytoplanktonic dynamic
during the study. No classification grouping the
other families of diatoms or dinoflagellates (
microplanktonic cells) can be observed in the
analysis, and this result is in accordance with
their episodic growths. These results allow the
description of the system using two different
groups of microplanktonic algae and one group of
nanoplanktonic algae.
Fig.14-MDS ordination of families (cells)
Fig.15-MDS ordination of taxa (carbon)
Fig.10-MDS ordination of communities (cells)
Fig.13-CLUSTER ordination of communities (carbon)
Fig12-MDS ordination of communities (carbon)
Fig.11-CLUSTER ordination of communities (cells)
Fig.16 k-dominance of communities (cells)
Fig.17 k-dominance of communities (carbon)
Fig.18 k-dominance of families (cells)
Fig.19 k-dominance of families (carbon)
References Clarke KF, Gorley RN, 2001.PRIMER User
Manual Tutorial. E-Primer Ltd, Plymouth Hill MO,
1973.Ecology 54, 427-432 Hillebrand H, Dürselen
CD, Kirschtel D, Pollingher U, Zohary T, 1999. J.
Phycol. 35, 403-424. Mendes-Deuer S, Lessard EJ,
2000. Limnol Oceanogr.45, 569-579 Moal J,
Martin-Jézéquel V, Harris RP, Samain JF, Poulet
SA, 1987. Oceanologica Acta 10,
339-346. Montagnes DJS, Berges JA, Harrison PJ,
Taylor FJR, 1994. Limnol. Oceanogr. 39,
1044-1060. Utermöhl H, 1958.Mitteilungen-Internati
onale Vereinigung für Limnlogie, 9, 1-38.
Fig.20-CLUSTER ordination of taxa families
(cells)
Fig.21-CLUSTER ordination of taxa families
(carbon)