藻华发生过程中胶州湾水体颗粒有机物脂肪酸的组成与动态

The composition and change of particulate fatty acids during a diatom bloom in Jiaozhou Bay,China

胶州湾在2005年夏季发生了中肋骨条藻(Skeletonema costatum(Grev.)Cleve)藻华,该优势种占细胞总量的比例在两个研究站位(C3站及A5站)分别达到59%和86%。对藻华发生过程中(7月,8月及9月份)的颗粒有机物进行了采样分析,测定了脂肪酸、叶绿素(Chl-a)和颗粒有机碳(POC)的浓度,分析了藻华发生过程中浮游植物和脂肪酸的组成特征,并通过标志脂肪酸对藻华发生过程中颗粒有机物组成的动态变化进行了分析。总脂肪酸浓度同叶绿素和颗粒有机碳浓度一样,在藻华发生期达到最高,两个采样站位(C3站及A5站)分别为29.0μg.L-1及185.5μg.L-1,比藻华发生前和消退后高2～3倍及20倍。胶州湾悬浮颗粒脂肪酸主要包括16∶0,14∶0,18∶0等直链饱和脂肪酸(SSFA),16∶1ω7、16∶1ω5+ω9、18∶1ω9,18∶1ω7等单不饱和脂肪酸(MUFA)及以20∶5ω3(DHA)和22∶6ω3(EPA)为主的多不饱和脂肪酸(PUFA)和以i-15∶0及ai-15∶0为主的支链饱和脂肪酸(BSFA)。藻华期与发生前相比,脂肪酸中的不饱和组分(MUFA,PUFA)所占比例在两个取样站位均有提高。随着藻华的消退,藻华区域中心的A5站的SSFA及BSFA比例有大幅提高,而在非藻华中心区域的C3站,不饱和脂肪酸尤其是ω3系列多不饱和脂肪酸(DHA,EPA等)比例的上升非常显著。藻华发生时浮游植物在颗粒有机物中的比重提高。藻华消退后,A5站颗粒有机物中碎屑有机物及细菌所占比重提高,而C3站颗粒有机物中浮游植物的比重仍然很高。浮游植物大量死亡是A5站藻华消退的主要形式,而C3站藻华的消退则可能与浮游动物的摄食有关。

The compositions of particulate organic carbon （ POC）, fatty acids （FA） and chlorophyll-a （Chl-a） and their correlations with phytoplankton groups were studied during a major diatom （Skeletonema costatum （Grey.） Cleve） bloom in July, August and September of 2005 in Jiaozhou Bay. The concentrations of Chl-a and POC peaked in the bloom stage （August） and the percentage of Skeletonema costatum （Grev.） Cleve reached to 86% in Station A5 and 59% in Station C3, dominated the phytoplankton species. Total particulate FA, followed the patterns of POC and Chl-a, also showed the highest concentrations in the bloom stage and that were 2 --3 times and 20 times higher at the two sampling stations C3 and AS, respectively, compared with the values measured in the pre- and post-bloom months （July and September）. The fatty acids were mainly composed of 16：0, 14：0, 18：0; 16：1ω7, 16：1ω5 ＋ω9, 18：1ω9, 18：1ω7; 20：5ω3 （DHA）, 22：6ω3 （EPA） and i/ai-15：0. Monounsaturated FA （MUFA） and polyunsaturated FA （PUFA） fractions were higher in the bloom stage than that in the pre-bloom stage at both stations. In the post-bloom stage, however, the percentages of straight chain saturated FA （SSFA） and branched chain saturated FA （BSFA） all increased while the MUFA and PUFA decreased significantly at Station A5, but increased conspicuously at Station C3, especially the ω3 components. The fate and composition changes of particulate FA indicate that phytoplankton （diatom） was the major contribution during the bloom month at both stations, while detritus and bacteria contributed significantly in the post-bloom stage at Station A5. It is suggested that the death of phytoplankton cells after the bloom largely reduced algal abundance in the diatom bloom at Station A5, but predation of zooplankton appeared to be the controlling factor for disappearance of the bloom at Station C3.