The brown alga Lobophora variegata, a bioindicator species for surveying metal contamination in tropical marine environments
Introduction
The main economic resources of New Caledonia are derived from nickel exploitation. The land-based open-cast mining activities inevitably result in direct and indirect metal contamination of the surrounding environment and in particular of the lagoon waters (Ambatsian et al., 1997, Labrosse et al., 2000). Although these metal inputs constitute a major threat to the local, highly diversified coastal marine ecosystems, little information is available regarding levels of contamination and possible impacts on the New Caledonian lagoon (Labrosse et al., 2000, Metian et al., 2005, Metian et al., 2008, Hédouin et al., 2006, Hédouin et al., 2007, Hédouin et al., in press).
Among the common approaches used to study environmental contamination, the use of bioindicator species has proved to be a valuable and informative tool. The main advantage of bio-monitoring approach compared to direct measurement in water or sediment is to provide a direct and time-integrated assessment of the metal fraction that is actually available to the organisms (bioavailable fraction) (e.g., Phillips, 1990, Phillips, 1994, Coteur et al., 2003, Danis et al., 2004). In the marine environment, bivalves are the most widely used bioindicator species and have been successfully used in the implementation of large scale monitoring programmes such as the US and European “Mussel Watches” (e.g., Goldberg et al., 1983, Warnau and Acuña, 2007). Although less commonly used, marine macrophytes and in particular seaweeds are well documented for their ability to concentrate contaminants from the surrounding waters (e.g., Bryan and Hummerstone, 1973, Burdon-Jones et al., 1982, Phillips, 1994, Warnau et al., 1996).
According to recent studies, the brown alga Lobophora variegata has been identified as a potential boindicator species for use in the New Caledonian lagoon (Breau, 2003, Hédouin, 2006). Indeed, this alga meets the criteria that a bioindicator species should fulfill (e.g., Phillips, 1994, Warnau et al., 2006), namely it shows a good capacity to bioconcentrate metals from its surrounding environment, is abundant, widely distributed and easy to collect (e.g., Coen and Tanner, 1989, Breau, 2003, Hédouin, 2006). However, no information is available on one of the most important pre-requisites to be met by a bioindicator species: the existence of a simple relationship between metal concentrations in organisms and those in seawater (e.g., Warnau et al., 1997). This is indeed the very criterion that allows the use of biota as reliable indicator of the metal contamination levels occurring in the environment. For this reason, the influence of ambient concentration of metals of local concern (Cd, Co, Cr, Mn, Ni and Zn) on their bioconcentration and depuration in L. variegata was investigated using the unique advantages of radiotracer techniques (Warnau and Bustamante, 2007) in order to further assess its value as a reliable sentinel species.
Section snippets
Sampling
Brown algae, Lobophora variegata (Lamouroux) Womersley, were collected by SCUBA diving in the south-western lagoon of New Caledonia (Maa Bay) in October 2003. This zone is considered as a relatively clean site in terms of metal contamination (Hédouin, 2006, Hédouin et al., in press). Three different morphological forms of L. variegata (ruffled, decumbent, and encrusting) have been described in the Caribbean; their occurrence depends on the habitat and intensity of herbivore predation (Coen and
Results
In Fig. 1 we show the uptake kinetics of the six metals in Lobophora variegata over the tested concentration ranges. Cd, Co, Cr and Zn were taken up according to linear uptake kinetics (R2 > 0.65) whereas Mn and Ni uptake were best described by a saturation model (R2 > 0.80) for each concentration tested (Table 1). All metals were readily incorporated in L. variegata at each tested concentration, with uptake rate constants ranging from 60 to 1,023 d− 1.
Linear Mix Model (LMM) analysis indicated that
Discussion
Among laboratory and field studies on accumulation capacities of Phaeophyceae representatives (e.g., Bryan and Hummerstone, 1973, Foster, 1975, Burdon-Jones et al., 1982) as well as their use in metal contamination biomonitoring programmes (e.g., Phillips, 1990, Amado Filho et al., 1999, Paez-Osuna et al., 2000), few studies have actually investigated the relationships between metal concentrations in brown algae and those in their environment. To the best of our knowledge, only Bryan (1969) has
Acknowledgements
The IAEA is grateful for the support provided to its Marine Environment Laboratories by the Government of Monaco. The authors thank D. Ponton (IRD-Noumea) for his help in SPSS statistical treatment, one Anonymous Reviewer for fruitful comments and O. Pringault and L. Breau (IRD-Noumea) for the shipment of organisms. LH was beneficiary of a CIFRE scholarship (France) supported by the Goro-Nickel Company, New Caledonia. MW is an Honorary Senior Research Associate of the National Fund for
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