汕头南澳龙须菜规模栽培对水质和浮游植物的影响

Large-scale cultivation of Gracilaria lemaneiformis in Nan'ao Island of Shantou and its effects on the aquatic environment and phytoplankton

为研究大型海藻龙须菜(Gracilaria lemaneiformis)规模栽培对水质和浮游植物的影响,于2016年3―6月在南澳深澳湾选择龙须菜栽培区(G)、鱼类养殖区(F)和对照区(C)3个采样区域,每个采样区域3个采样点,进行每月1次的采样调查。对海水温度(WT)、盐度(salinity)、pH、溶氧(DO)、总氮(TN)、总磷(TP)、无机氮(DIN)、无机磷(DIP)、叶绿素a(Chl a)和浮游植物密度进行测试分析。结果表明:(1)在龙须菜栽培期和收获期(3―5月),龙须菜栽培区的pH和DO均显著高于其余区域(P<0.05),收获后各区域无显著性差异(P>0.05);(2)在龙须菜栽培期(3―4月),栽培区的TN、TP、DIN和DIP含量均显著低于对照区和鱼类养殖区(P<0.05);(3)龙须菜栽培期间和收获期(3―5月)栽培区浮游植物密度显著低于其他区域(P<0.05),龙须菜收获后(6月),3个采样区域浮游植物的密度大幅上升;(4)2016年南澳海域共收获龙须菜49729 t,据估算,龙须菜规模栽培从海水中移除了2212 t N、174 t P和13300 t C,至少释放了34700tO_2。研究表明,龙须菜规模栽培能有效去除N、P营养盐,防治海洋富营养化;提高栽培区域的pH和DO,有利于防治海洋酸化和低氧问题;降低浮游植物密度,抑制有害藻华的发生。

Seaweeds are the major primary producers,and play a vital role in coastal ecosystems.Since 2000,large-scale cultivation of Gracilaria lemaneiformis has rapidly developed along the Chinese coast.Nan’ao island is an important base for G.lemaneiformis cultivation in Guangdong.In order to study the effects of large-scale seaweed cultivation on the aquatic environment and phytoplankton,monthly surveys were carried out in the cultivation area of Shen’ao Bay in Nan’ao island from March to June 2016.In this study,fish culture area (F),Gracilaria culture area (G),and control area (C) without Gracilaria cultivation activities were selected for sampling.There were three sampling points per area,marked as F1,F2,F3,G1,G2,G3,C1,C2,and C3,respectively.Four surveys were undertaken on March 25,April 24,May 23,and June 22,2016.March and April were the cultivation periods,while May was the harvest period,and in June,no Gracilaria was cultured.Dissolved oxygen (DO),pH,total nitrogen (TN),total phosphorus (TP),inorganic nitrogen (DIN),inorganic phosphorus (DIP),phytoplankton density,and chlorophyll a (Chl a) contents were measured.Moreover,the amount of N,P,and C removed from seawater and the amount of O2 released to seawater by G.lemaneiformis were estimated based on the statistical data from Nan’ao in 2016.The results showed that pH and DO in the Gracilaria culture area were significantly higher than those in other regions (P<0.05) from March to May,with no significant difference (P>0.05) between the sampling areas after seaweed harvest (June).The contents of TN,TP,DIN,and DIP in the Gracilaria culture area were lower than those in other areas (P<0.05) from March to April.Similarly,phytoplankton densities and Chl a contents were significantly lower in the Gracilaria culture area than those in other areas (P<0.05).The total produce of G.lemaneiformis in Nan’ao island for 2016 was 49729 t,removing 2212 t of N,174 t of P,and 13000 t of C from seawater while releasing 34700 t of O2 to seawater.Our results show that large-scale cultivation of G.lemaneiformis could effectively remove N and P,improve pH and DO,and inhibit phytoplankton growth.This has the potential to control seawater eutrophication,mitigate the impacts of ocean acidification and hypoxia,and prevent harmful algal blooms.