Trace elements and primary production of Posidonia oceanica at the edge of natural and anthropogenic patches in the Revellata Bay (Calvi, Corsica, France)

Supervisor: Sylvie Gobert (Univ. Liege)
Posidonia oceanica is an endemic seagrass in the Mediterranean and represents the most productive ecosystem in the world. They constitute an engineering ecosystem and play a major ecological, geological and economic role. At diverse spatial and temporal scale, an enormous amount of pollutants is impacted on this highly productive meadow. Various anthropogenic activities including shipping and navigation, tourism, trawling and anchoring have declined Posidonia oceanica leaves, rhizomes and roots by breaking or uprooting them. As a result, the areas have become empty of Posidonia oceanica which are named sandy “patches”. Posidonia oceanica meadows are naturally fragmented by hydrodynamic as well as water movements. One side is eroded by marine currents when the meadow colonized at the opposite site.  This study aims at measuring the level of risks of the biodiversity of the Revellata Bay by concentrating on the trace elements and primary production of P. oceanica at the natural and anthropogenic patches of this area. For this purpose, four selected sampling sites were compared. A continuous meadow, natural patch (a colonizing meadow, an erosive meadow) and an impacted meadow of anchoring area were selected as sampling site. The selected parameters were the annual primary production of Posidonia oceanica, the biomass, the C/N contents and the trace element concentrations in shoots.  Our goal was to measure the spatial variability of major parameters (primary production, biomass, carbon/nitrogen contents and trace element concentrations).The natural colonizing meadow showed maximum values of leave’s primary production (2111 gDW.m-2.year-1) and biomass (441.88 ± 167.53 gDW.m-2).The highest values of C: N (21.37 ± 1.96) contents were found in the continuous meadow. Concentrations of Be, Al, V, Mn, Co, As, Se, Mo, Ag, Sn, Sb, Bi, Cr, Fe, Ni, Cu, Zn, Cd and Pb were analysed in P. oceanica shoots. The first twelve trace elements (Be, Al, V, Mn, Co, As, Se, Mo, Ag, Sn, Sb, Bi) are considered as potential pollutants. Among them, high concentrations of Al, Mn, Co, As and Se were found in an impacted meadow of Anthropogenic patch. Compared to other sites, Be, V, Sr, Ag and Sb concentrations were measured at higher concentrations in the meadow of the natural patch. Mo and Sn concentrations were detected at high levels in the continuous meadow than other sites. Some Trace elements such as Cu and Ni are essential for seagrass as a micronutrient. However, high levels of Fe, Cd, Pb and Zn, Cu, Ni, Cr were found in the meadow of the natural patch and continuous meadow respectively. Spatial variations were found for all trace elements except for Be, Mo, Ag and Sb concentrations. The results reflect and confirm the background concentrations of trace elements in the study area.