Heavy Metal Depuration Steps for Gracilaria chilensis in Outdoor Culture Systems

Abstract

Seaweed aquaculture is affected by natural and anthropogenic stressors, which put the biomass productivity of the cultures at risk. Seaweed biomass for commercial purposes, principally in pharmaceutical and/or nutraceutical applications, needs to be free of pollutants; therefore, controlled cultures have relevance in regulating the quality of biomass. The aim of this work was to demonstrate the successful utilization of controlled outdoor cultures to remove excess heavy metal accumulation in Gracilaria chilensis, an important commercial seaweed farming model. Specifically, we designed a simple and operational heavy metal depuration protocol, utilizing seawater and tap water removal, which permitted the concentration reduction of 10 heavy metals, including As, Cu, and Cd but not Zn, from the biomass at 7 days of culture. The percentage of depuration of the heavy metals ranged from 32 to 92% at 7 days, which was maintained throughout 21 days of culture. During the culture period, the monitored physicochemical parameters (temperature, salinity, and dissolved oxygen, among others) remained stable, with an increase in the daily growth rate (DGR% d−1) of the biomass recorded after 14 days of culture. Consequently, the experimental setup was successful for heavy metal depuration, which highlights the importance of controlled outdoor cultures as important tools of sustainability.

Indoor and Outdoor Cultures of Gracilaria chilensis: Determination of Biomass Growth and Molecular Markers for Biomass Quality Evaluation

“…The initial vegetative biomass of G. chilensis (200 kg) was collected from Ancud, Chile (41°52′06″ S, 73°49′43″ W) and transported in cool conditions using ice packs to the Quintay Marine Research Center (CIMARQ). For the cultures, the methodologies proposed by the authors of [ 14 , 15 ] were used, which consisted of washing the biomass using tap water for 1 h. Then, the biomass was maintained and acclimatized for one week in outdoor raceways of 3000 L. In a constant flow of seawater filtered at 100 µm, covered with Raschel mesh with 80% light filtration, constant aeration, 32.3 PSU of salinity, and a light intensity between 150 and 230 µmol m –2 s –1 .…”

“…Among the current methodologies for seaweed cultivation, indoor and outdoor cultivation systems control biomass growth and quality without negative externalities on the environment [ 13 , 14 , 15 ]. According to the authors of [ 14 ], the benefits of indoor and outdoor cultivation systems include possible fertilization, i.e., supplying nutrients in adequate amounts to obtain positive cell growth [ 16 , 17 ], as well as the removal of contaminants from the biomass, such as heavy metals, ensuring a high quality [ 15 ].…”

“…Among the current methodologies for seaweed cultivation, indoor and outdoor cultivation systems control biomass growth and quality without negative externalities on the environment [ 13 , 14 , 15 ]. According to the authors of [ 14 ], the benefits of indoor and outdoor cultivation systems include possible fertilization, i.e., supplying nutrients in adequate amounts to obtain positive cell growth [ 16 , 17 ], as well as the removal of contaminants from the biomass, such as heavy metals, ensuring a high quality [ 15 ]. One of the most commonly used media is Von Stosch (VS), due to its contribution of nitrogen, phosphorus, trace metals (such as manganese and iron, among others), and vitamins such as B 12 , B 7 , and B 1 , which have been shown to be effective in laboratory-scale indoor cultures for the initial development stages of red algae species [ 18 , 19 ].…”