Author: Philippe Richir

Seagrass response to in situ trace element contaminations
J. Richir , N. Luy, G. Lepoint, R. Biondo, S. Vermeulen, S. Gobert
Laboratory of Oceanology, University of Liège ULg, Liège, Belgium

Introduction
The endemic Mediterranean seagrass Posidonia oceanica has been successfully used since the mid-1970s in the biomonitoring of trace elements (TE) in coastal areas (1, 2). However, there is still a lack of knowledge regarding contamination kinetics in this species (3).

Material and methods
This study was conducted in the Calvi Bay (Corsica, NW Mediterranean) in June 2009. Posidonia were isolated in a 410 L PVC mesocosm anchored at 10m depth in the meadow (Photo 1, Fig. 1). The contamination lasted for 6 days and was performed using a cocktail of 15 trace elements (TE: Cu, Pb, Al, V, Cr, Mn, Fe, Co, Ni, Zn, As, Mo, Ag, Cd and Bi). Pollutant levels within the mesocosm were similar to those measured in contaminated areas. Bioavailable dissolved TE were monitored with DGTs (chelex-type resins). TE concentrations were measured by DRC-ICP-MS in leaves and rhizomes (Fig.2) sampled at regular time intervals.

Fig. 1: PVC bell-shaped mesocosm. Rounded letters - A. Posidonia shoots; B. pump; C. DGT; D. temperature
probe. Pollutants added twice a
day at 9 am and 9 pm.

Fig. 2: Posidonia shoots - A. leaves inserted on rhizome;
B, C. adult leaves; D. intermediate leaf; E. juvenile leaf.

Photo 1: Mesocosm in Posidonia bed (10m depth)

Results and Discussion
Posidonia shoots immediately accumulated pollutants at the beginning of the experiment (fig. 3A). Once contaminations ended, TE concentrations felt to their background levels within a 2 weeks delay, or at least showed a clear decrease. Likely because of their distinct metabolism, shoot compartments showed clear differences in uptake and detoxification kinetics (fig. 3B): intermediate young growing leaves (IL) incorporated chemicals faster than the old senescent ones (AL); rhizomes did not show any clear trend (excepted for Cu, Zn, Bi).

A

B

Fig. 3: Representative profiles of (A) Pb and Cu kinetics in leaves and (B) tissue compartmentalization. Concentrations in Posidonia tissues are given in µg.g-1 of dry weight (DW). For Fig. A, right y axis refers to concentrations in seawater measured with DGTs in µg.L-1.

Conclusions
Posidonia is a sensitive sentinel to delineate punctual pollutions. The good response of leaves to short term contaminations confirms their great reliability for routine monitoring purpose. The use of rhizomes allows to bypass both the deciduous character of Posidonia leaves and their ability to detoxify rapidly. They also provide additional informations regarding long term pollutions.

References:
1. Luy et al. (in press). Ecological Indicators. 2. Pergent et al. (2005) - Ecological Indicators. 5:213-230. 3. Warnau et al. (1996). Marine Environmental Research. 41:343-362.
Acknowledgments:
This work was funded by the Belgian National Fund for Scientific Research FRS-FNRS. Authors are thankful to the Oceanographic Station STARESO for field work and facilities.
Corresponding author E-mail and references:
jonathan.richir@ulg.ac.be - http://orbi.ulg.ac.be/
Author bibliography is available on http://orbi.ulg.ac.be/