The spatial variability of trace element bioaccumulation processes: Tools to environmental management

摘要

As transitional environments, coastal meadows are particularly vulnerable to pollution. Trace elements remain contaminants of concern because of their persistence, their ability to accumulate in biota and their toxicity. Local, regional, national and cross-border programs are thus initiated to monitor their environmental occurrence. Sentinel organisms, or bioindicators, have been widely used to this end since they accumulate the bioavailable and thus potentially toxic fraction of contaminants. In the framework of the STARECAPMED project, the accumulation of trace elements in the seagrass Posidonia oceanica (L.) Delile was studied at different spatial scales: along a radial (100 m scale), in a bay (1 km scale), along the French Mediterranean littoral (10-100 km scale) and along the whole Mediterranean coastline (100-1000 km scale). Results showed that the contamination of the sampled shoots could vary as much at opposite scales. This benthic primary producer accumulates contaminants sequestered in the sediments, in addition to their dissolved fraction in the water column. The sediments also offer a time integration of coastal pollution and thus amplify the pollution signal recorded by the seagrass, resulting in the observed spatial variability. These results demonstrate that the in-depth knowledge of the ecology of the monitored bioindicator and the interactions it shares with its environment cannot be ignored. Such failure could lead to erroneous interpretations of the levels of contamination of monitored sites, and points out the need to define a sampling strategy based on the monitoring objectives and the selected bioindicator.