Marine macroalgae as active biomonitors: Evaluation of multi-element bioconcentration kinetics in Dictyota spiralis and Laurencia microcladia

Brown and red macroalgae are promising biomonitors of inorganic pollutants in marine environments, due to quick growth, high biomass, ease of sampling and the production of a diverse array of chelating agents. The limited distribution and low population densities of most of the currently adopted species, however, prompt the need to search for suitable alternatives. To this end, the accumulation kinetics of ten metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V, Zn) and one metalloid (As) under field-conditions were studied in Dictyota spiralis and Laurencia microcladia, brown and red macroalgae, respectively. Specifically, element concentrations were measured at 0, 2, 4, 8, 16 and 24d on algae (both alive and devitalized) exposed in the field (through purposely developed bags) in 4 sites differing in anthropogenic impacts along the Tyrrhenian coast (southern Italy). Robust Bayesian analyses were adopted for model fitting and selection, as well as to derive posterior distributions for parameters with straightforward practical implications for biomonitoring of coastal waters. Kinetics followed pseudo-first order, pseudo-second order and two-phase intraparticle diffusion models, with saturation times varying among elements, between species and between devitalization treatments. The spatial discrimination capability of the species varies in relation to the element, with a distinct advantage of living L. microcladia for the biomonitoring of Co, Cr, Cu, Fe, Mn and V, and of devitalized D. spiralis for the biomonitoring of As, Cu, Ni, Pb and Zn. Overall, findings highlight the remarkable effectiveness of transplants of both the species for the active biomonitoring of marine coastal ecosystems, especially when leveraging over their complementary selectivity toward different elements. The specificity in accumulation behavior allows also diversifying the target use of the two species, suggesting shorter-term monitoring and even bioremediation applications in the case of D. spiralis.