Bioremediation efficiencies of Gracilaria verrucosa cultivated in an enclosed sea area of Hangzhou Bay, China Yuan Zi Huo & Shan Nan Xu & Yang Yang Wang & Jian Heng Zhang & Yin Jiang Zhang & Wei Ning Wu & Ya Qu Chen & Pei Min He Received: 23 January 2010 / Revised and accepted: 20 August 2010 / Published online: 3 September 2010 # Springer Science+Business Media B.V. 2010 Abstract Due to the discharge of nutrients into the East China Sea, severe eutrophication has appeared in Hangzhou Bay. Therefore, we cultivated Gracilaria verrucosa on a large scale in the Jinshan enclosed sea with an area of 1.72 km 2 in the northern part of Hangzhou Bay to perform bioremediation. The Fengxian enclosed sea with an area of 2.3 km 2 and 50 km far from Jinshan was used as the control. The results showed that the Hangzhou Bay was severely eutrophicated before G. verrucosa cultivation. During the period of cultivation between August 2006 and July 2007, the annual growth rate of G. verrucosa was 9.42% day -1 , and the sea water quality was improved from worse than grade IV to grades II–III, with the concentration of dissolved inorganic nitrogen (DIN) and PO 4 -P signifi- cantly lower than that in the Fengxian enclosed sea (p < 0.01). The concentration of NH 4 -N, NO 3 -N, NO 2 -N, and PO 4 -P after G. verrucosa cultivation was decreased by 54.12%, 75.54%, 49.81%, and 49.00%, respectively. The density of phytoplankton in the Jinshan enclosed sea with cultivation of G. verrucosa was 6.90 –126.53×10 4 cells m -3 , which was significantly lower than that in the Fengxian enclosed sea. In addition, species diversity, richness, and evenness was significantly increased after cultivation of G. verrucosa in the Jinshan enclosed sea compared with that in the Fengxian enclosed sea. The density of Skeletonema costatum, Prorocentrum micans, and Prorocentrum donghaiense, which were the usual species of red tides at the coastal sea of China, in the Jinshan enclosed sea with cultivation of G. verrucosa was significantly lower. Based on these results, if the water quality in the Jinshan enclosed sea were to be maintained at grade I (DIN ≤0.20 mg L -1 ) or II (DIN ≤0.30 mg L -1 ), 21.8 t or 18.0 t fresh weight of G. verrucosa need to be cultivated, respectively. These results indicated that large- scale cultivation of G. verrucosa could play a significant role in the bioremediation of Hangzhou Bay. Keywords Eutrophication . Rodophyta . Seaweeds . Red tides . Nutrient reduction efficiency . East China Sea Introduction Eutrophication is generally considered as the principal cause of red tides and the deterioration of marine coastal environments (Schramm et al. 1996). The coastal area is closely associated with human economic activities and has become an important region for human society. Over the last few decades, eutrophication of coastal seas has been aggravated by human activities (Schramm 1999; Capriulo et al. 2002). In coastal areas of China, rapid population increases and human activities such as agricultural produc- tion, discharge of industrial wastewater, urban runoff, and large-scale finfish and shrimp aquaculture have caused large inputs of nutrients (He et al. 2008), many times greater than those generated by natural processes (Victor et al. 2002), and many areas exhibit typical symptoms of eutrophication (Xu and He 2006). The detrimental effects This paper was presented at the 7th Asia Pacific Congress on Algal Biotechnology, New Delhi 2009. Y. Z. Huo : S. N. Xu : Y. Y. Wang : J. H. Zhang : Y. J. Zhang : W. N. Wu : P. M. He(*) College of Fisheries and Life Sciences, Shanghai Ocean University, Shanghai 201306, China e-mail: pmhe@shou.edu.cn Y. Q. Chen East China Sea Fishery Research Institute, Chinese Academy of Fishery Sciences, Shanghai 200091, China J Appl Phycol (2011) 23:173–182 DOI 10.1007/s10811-010-9584-9