Biometry, and fatty acid and fatty alcohol composition of the Arctic ctenophore Mertensia ovum from Kongsfjorden@en

Lipids of the Arctic ctenophore Mertensia ovum, collected from Kongsfjorden (Svalbard) in 2001, were analysed to investigate seasonal variability and fate of dietary lipids. Total lipids, lipid classes and fatty acid and alcohol compositions were determined in animals, which were selected according to age-group and season. Changes in lipids of age-group 0 animals were followed during growth from spring to autumn. Total lipids increased from May to September. Lipids as percentage of dry mass were lowest in August indicating their use for reproduction. Higher values occurred in September, which may be due to lipid storage for overwintering. Wax esters were the major lipid class accounting for about 50% of total lipids in age-group 0 animals from July and August. Phospholipids were the second largest lipid fraction with up to 46% in this age-group. The principal fatty acids of M. ovum from all age-groups were 22:6(n-3), 20:5(n-3) and 16:0. Wax ester fatty alcohols were dominated by 22:1(n-11) and 20:1(n-9) followed by moderate proportions of 16:0. The unique feature of M. ovum lipids was the high amount of free fatty alcohols originating probably from the dietary wax esters. In May, free alcohols exhibited the highest mean proportion with 14.6% in age-group 0 animals. We present the first data describing a detailed free fatty alcohol composition in zooplankton. This composition was very different from the alcohol composition of M. ovum wax esters because of the predominance of the long-chain monounsaturated 22:1 (n-11) alcohol accounting for almost 100% of total free alcohols in some samples. The detailed lipid composition clearly reflected feeding of M. ovum on the herbivorous calanoid species, Calanus glacialis and C. finmarchicus, the abundant members of the zooplankton community in Kongsfjorden. Other copepod species or prey items seem to be less important for M. ovum.本研究对2001年采自斯瓦尔巴群岛（Svalbard）孔斯峡湾（Kongsfjorden）的北极栉水母美肋栉水母（Mertensia ovum）的脂质组分开展分析，旨在探究膳食脂质的季节变异规律与代谢归宿。研究人员依据年龄组与采样季节对研究个体进行筛选，随后测定其总脂质含量、脂质类别组成以及脂肪酸与脂肪醇的组成特征。本研究追踪了0龄组个体在春季至秋季生长过程中的脂质变化情况：总脂质含量自5月至9月呈持续上升趋势；以干重百分比计的脂质含量在8月降至最低，表明此时脂质被用于生殖活动；9月脂质含量回升，这或与个体越冬前的脂质储备行为相关。蜡酯（wax esters）是0龄组个体的主要脂质类别，在7月与8月时约占总脂质的50%；磷脂（phospholipids）为该年龄组第二大脂质组分，占比最高可达46%。所有年龄组美肋栉水母的主要脂肪酸为22:6(n-3)、20:5(n-3)与16:0；蜡酯结合的脂肪醇以22:1(n-11)与20:1(n-9)为主，同时伴有占比中等的16:0。美肋栉水母脂质的独特特征为其含有大量游离脂肪醇，其来源或为膳食中的蜡酯；5月时，0龄组个体的游离脂肪醇平均占比最高，达14.6%。本研究首次提供了浮游动物中详细的游离脂肪醇组成数据，该组成与美肋栉水母蜡酯的脂肪醇组成差异显著——部分样本中长链单不饱和的22:1(n-11)醇几乎占总游离脂肪醇的100%。细致的脂质组成分析清晰表明，美肋栉水母的主要摄食对象为孔斯峡湾浮游动物群落中的优势植食性哲水蚤类（calanoid）物种：冰川真哲水蚤（Calanus glacialis）与芬氏真哲水蚤（C. finmarchicus），其他桡足类物种或猎物对象对美肋栉水母而言重要性较低。