Elemental Fractionation in Sabellariidae (Polychaeta) Biocement and Comparison with Seawater Pattern: A New Environmental Proxy in a High-Biodiversity Ecosystem?

The polychaete worm Sabellaria alveolata builds shallow-water aggregates of tubes by agglutinating sands using a secreted glue. Sabellarid bioconstructions represent fragile and dynamic habitats that host numerous associated organisms, playing a key ecological role. A two-year study on bioconstructions from three Sicilian sites (Simeto, Portopalo, and Falconara) investigated the balance between reef status and environmental parameters through a geochemical comparison of biocement tube portions and the surrounding waters. Water pollution by heavy metals, which is monitored in marine waters, is a result of river, domestic, and industrial discharges. The major constituents from the biocements of the three sites showed concentrations comparable to those in the seawater, while trace elements (Cr, Ni, Cu, Zn, and As) showed concentrations significantly higher than the mean seawater composition. These similar trends confirm a close dependence between the presence of trace elements (metals) in the seawater and the subsequent bioaccumulation in the biocement produced by the worm. The results also showed that Ca and Mg are fractionated by biocement independent of their water concentrations, in contrast to the trace elements. Further studies addressing the biomineralization processes and the relative fractionation of trace elements in Sabellaria biocement will allow it to be validated as a valuable proxy for short- and long-term environmental studies.