Macroalgae culture–induced carbon sink in a large cultivation area of China

Macroalgae culture–induced carbon sink in sediments has been little investigated. Here, total organic carbon (TOC), total nitrogen (TN), and δ 13 C were examined in sediments in a cultivation field of macroalgae (kelp and Gracilariopsis lemaneiformis ) in Sansha Bay, Southeast China. Both proxies of C/N (TOC to TN ratio) and δ 13 C indicated a multisource of TOC. Based on a three-endmember model, macroalgae-derived TOC ( TOC ma ) accounted for < 35% of the total TOC, averaging 16 ± 9% (mean ± SD). On average, terrestrial and phytoplankton-derived TOC showed much higher percentages of 24 ± 17% and 60 ± 20%, respectively ( t -test, p < 0.02). A preliminary estimate suggested that TOC ma represents a carbon sink of 8.2 × 10 3 tons per year, corresponding to about 22% of the sink associated with phytoplankton and macroalgae and 8 ± 6% of the macroalgae carbon production in Sansha Bay. Considering its production magnitude, the macroalgae-induced carbon sink seems to be insignificant, on a national or global scale, to phytoplankton, though it should be taken into account given the small cultivation area.