Cadmium and copper accumulation and toxicity in the macroalga Gracilaria tenuistipitata

The macroalga Gracilaria tenuistipitata is widely distributed in the coastal waters of southern China, and is extensively used as the main food source in abalone aquaculture. However, it also possesses a high ability to accumulate trace metals in its tissues. This study investigated the accumulation of cadmium (Cd) and copper (Cu) in this macroalga under various temperatures and salinities, and the subsequent influences on growth rate, lipid peroxidation, and total energy reserve. The accumulation of both Cd and Cu was enhanced with increasing temperature and decreasing salinity. The bioaccumulation factor of Cu was ~10 times higher than that of Cd. Changes in temperature, salinity and accumulated metals all affected the tested biomarkers to some extent. We demonstrated that growth rate, lipid peroxidation level and total energy reserve were all significantly correlated with the accumulated tissue Cu concentrations, suggesting that Cu accumulation in the tissue can be used as a proxy for measuring Cu toxicity in G. tenuistipitata under various environmental conditions. In contrast, among the 3 toxic endpoints, only growth rate was inversely related to the Cd tissue concentrations. Cu exerted a greater toxic effect on G. tenuistipitata than Cd, largely due to its different toxicological mechanisms and biological accumulation potentials. Cd appeared to have no profound influence on the production of reactive oxygen species. A higher Cd accumulation at lower salinity did not cause a stronger growth inhibition as compared to Cu. Given the commercial value of the macroalga as a main food source in abalone aquaculture, Cu contamination and high temperature should be avoided in the culture of G. tenuistipitata, because they can reduce its energy reserves.