基于脂肪酸标记法和碳氮稳定同位素比值法的东海水母常见种的食性分析

采用脂肪酸标记法和碳氮稳定同位素比值法研究了东海6个水母常见种的食性。结果表明,6种水母的总脂肪酸含量都不高,说明作为饵料,水母不能够给捕食者提供较多的脂类营养物质。蝶水母(Ocyropsis crystallina)、瓜水母(Bero cucumis)和四叶小舌水母(Liriope tetraphylla)的脂肪酸组成较为相近,它们更多地通过捕食食物链获得有机质。同时,这几种小型水母摄食浮游植物(主要是硅藻和甲藻)比其它几种水母多;另外,它们对植食性桡足类也有一定的摄食。4月份墨绿多管水母(Aequorea coerulescens)主要通过腐生食物链获取有机质;另外,其对植食性桡足类也有一定的摄食。双生水母(Diphyidae spp.)参与腐生食物链也较多;另外,20:1+22:1含量较低指示了其对植食性桡足类几乎不摄食。蝶水母、瓜水母、四叶小舌水母和沙海蜇(Nemopilema nomurai)的δ13C更接近于陆源的C4植物的δ13C,说明其受陆源影响较大。δ15N特征结果表明,蝶水母、瓜水母和四叶小舌水母(Liriope tetraphylla)在浮游食物网中均处于较高营养级,沙海蜇虽个体较大,但由于其摄食器官较小,故其与这3种小型水母的营养地位相近。并且相对于其它几种水母,沙海蜇细菌脂肪酸标记更为明显。

THE DIET OF THE COMMON MEDUSA SPECIES IN THE EAST CHINA SEA REVEALED BY FATTY ACID AND STABLE CARBON AND NITROGEN ISOTOPIC ANALYSIS

Fatty acid compositions and stable isotope ratios of carbon and nitrogen were used to identify the diet of six common medusa species in the East China Sea,Ocyropsis crystalline,Bero cucumis,Liriope tetraphylla,Diphyidae spp.,Aequorea coerulescens,and Nemopilema nomurai.Analysis of the fatty acid composition showed that the total fatty acids of three medusae were low,which reflecting their lower lipid nutritional values.O.crystalline,B.cucumis and L.tetraphylla showed similar fatty acid compositions.Firstly,they all had a higher content of 16:1ω7 and 18:4ω3,indicating feeding on phtytoplankton(mostly diatoms and dinoflagellates) more than the other medusae.Secondly,the higher contents of 20:1+22:1 reflected herbivorous copepods are parts of their food items.In addition,they were characterized by high contents of Σω3,accumulated via the grazing food chain.By contrast,A.coerulescens was characterized by an increase in Σω6 of macroalgal origin,which was transferred via the detritus food chain.Otherwise,it also fed on herbivorous copepods in view of the fatty acid 20:1+22:1.The higher Σω6 contents also indicated that Diphyidae spp.accumulated via the detritus food chain,and it fed little on herbivorous copepods.The δ13C of O.crystalline,B.cucumis,L.tetraphylla and N.nomurai were similar to C4 plants,indicating significant contribution of C4 plants to the nutritions of four medusae.The δ15N of the six medusae indicated their higher trophic levels in plankton food web.Although N.nomurai is big,it located at a similar trophic level as O.crystalline,B.cucumis and L.tetraphylla,because of its smaller terminal pore.In addition,the marker of Bacteria FA was evident in N.nomurai.