On the effectiveness of the red alga Laurencia microcladia as a PAH biomonitor in coastal marine ecosystems.

Anthropogenic pressures affect large stretches of Mediterranean coastal environments, determining alterations, including chemical pollution, able to impair ecosystem functioning and services. Among the pollutants of major concern for their toxicity and persistence, there are polycyclic aromatic hydrocarbons (PAHs), which can be effectively monitored through bioaccumulation approaches. However, the main biomonitor of PAHs in the Mediterranean Sea, Posidonia oceanica, is currently undergoing extensive regressions due to anthropogenic pressures, forcing the search for alternative biomonitors. In this context, with a view to evaluate the effectiveness of the red alga Laurencia microcladia as an alternative PAH biomonitor, we comparatively investigated the accumulation gradients of 14 PAHs in its thalli, in leaves of P. oceanica and in surface sediments collected from different sites along the Cilento coast (southern Italy). The two species mainly absorb PAHs from water rather than sediments and show comparable PAH concentrations, with a preferential accumulation of low molecular weight PAHs in L. microcladia and of medium molecular weight PAHs in P. oceanica. Although with different accumulation profiles, both macrophytes highlighted comparable concentration gradients of anthracene and benzo[a]pyrene across study sites and the highest concentrations near a harbour. The obtained findings indicate that L. microcladia can be considered an effective biomonitor of PAHs in coastal ecosystems.