What dead seaweeds can tell us about metal uptake and their application to control marine pollution.

The mechanisms of trace element uptake by seaweeds are still unknown, despite being key to understand the impact of pollution in coastal environments. This knowledge gap, in addition to the lack of standardization, have also hindered the use of seaweeds to monitor seawater pollution. To address these shortcomings, we tested the use of devitalization as a pre-exposure treatment for brown seaweed transplants, and we compared devitalized and fresh transplants to gain some insights into the mechanisms of element uptake. We exposed four types of Fucus vesiculosus transplants in 6 sites for 4, 8 and 20 days: fresh and devitalized (dried or boiled) algal segments held in mesh bags, and whole algal thalli imitating natural conditions. We then determined he concentrations of 11 trace elements in the algal tissues. The element concentrations were highest in the devitalized transplants, but the material lost consistency and weight throughout the exposure period, limiting their use to short periods. We proposed several factors that may contribute to the different accumulation patterns between treatments, and examined the implications for the uptake mechanisms, revealing that two of the most important are surface adsorption of sediment particles and chemical bounds to extracellular components.