Effects of Tissue Nitrogen and Media Nitrate on Trace Metal Uptake and Trophic Transfer by Ulva spp.

A general survey of trace metal content in Ulva spp. (Linnaeus) around Moss Landing, California was carried out. The next objective was to evaluate whether tissue nitrogen or media nitrate affects metal uptake (As, Pb, Mn, Zn) by Ulva spp. under eutrophic conditions. Additionally, the role of metal burden in the invertebrate Idotea resecata as a function of metal content in its diet was examined. Mean trace metal concentrations in Ulva differed significantly among sites in Moss Landing, California. Laboratory measurements using samples from 15 sites along the central California coast revealed a significant positive correlation between Ulva spp. tissue nitrogen and both arsenic and manganese uptake. No relationship was found between tissue nitrogen and lead or zinc, but a significant positive correlation with the relative change in manganese and lead was observed. Though statistically insignificant, a regression analysis revealed a logarithmic relationship between media nitrate and both tissue arsenic and manganese. Lead and zinc content in Ulva had no relationship with media nitrate. Metal in Idotea resecata was not significantly related to diet treatments; however, a bioaccumulation trend was observed for arsenic and manganese. Given the role of trace metals in the production of photosynthetic enzymes and proteins, variability in productivity may drive the uptake of essential and non-essential elements. Depending on the amount of Ulva consumed, elevated metal content in these macroalgae could pose a health risk to invertebrates and/or humans