Elevated trace elements in Posidonia oceanica and Cymodocea nodosa at six Mediterranean volcanic seeps

Abstract

Seagrasses form important habitats around shallow marine CO2 seeps, providing opportunities to assess trace element (TE) accumulation along gradients in seawater pH. Here we assessed Cd, Cu, Hg, Ni, Pb and Zn levels in sediment and seagrasses at six CO2 seeps and reference sites off Italy and Greece. Some seep sediments had much higher concentrations of TEs, the extreme example being Cd at 43-fold above reference levels. Sediment Quality Guideline (SQG) scores indicated that three seeps had sediment TEs levels likely to have \"Adverse impacts\" on marine biota; namely Vulcano (for Hg), Ischia (for Cu) and Paleochori (for Cd and Ni). SQG indicated seep sediments of Italian seeps were adversely affected by Cu and Hg, whereas Greek CO2 seeps were affected by Cd and Ni. An increase in sediment TEs levels positively corelated with higher levels of TEs in seagrass roots of Posidonia oceanica (Zn and Ni) and Cymodocea nodosa (Zn). Differences in the bioavailability and possible toxicity of TEs helps explain why seagrasses were abundant at some CO2 seeps but not others.