Differential accumulation patterns of heavy metals among the dominant macrophytes of a Mediterranean seagrass meadow

Marine macrophytes are not only key-elements in the cycling of elements in shallow, nearshore ecosystems, often significantly enhancing bioavailability of toxic substances to higher consumers, but are in turn also adversely effected by such pollutants. Mediterranean seagrass meadows rank among the highly threatened marine ecosystems, and detrimental impacts of trace metal pollution are likely to accentuate their vulnerability further. The Gulf of Naples may serve as one region with potential pollution problems, and to contribute to a broad assessment of threads to benthic ecosystems in this region, contamination loads of the heavy metals Cu, Zn, Cd and Pb were quantified in the seagrass Posidonia oceanica and three species of macroalgae which are abundant in the seagrass beds. Trace metal levels differed significantly among all macrophyte species analysed. Except for Cd, interspecific differences in metal loads were just as distinct among the algae as they were between the algae and the seagrass. This implies that there is little justification to view marine macrophytes as a single homogenous groups with respect to trace metal dynamics. Because sampling encompassed the same environmental variability for all species, differences in the accumulation dynamics of trace metals reflect taxonomic differences in physiology and not environmental variation as such. Much of the evidence at hand for judging overall environmental contamination from organismʹs tissue concentrations depends on both the species of metal and the type of organism chosen. Consequently, the striking differences in accumulation behaviour exemplified in this study, both among metals and among species, caution against restricting environmental pollution analysis to one or a few ‘indicator’ organisms.