Functional diversity and nutritional content in a deep-sea faunal assemblage through total lipid, lipid class, and fatty acid analyses

Lipids are key compounds in marine ecosystems being involved in organism growth, reproduction, and survival. Despite their biological significance and ease of measurement, the use of lipids in deep-sea studies is limited, as is our understanding of energy and nutrient flows in the deep ocean. Here, a comprehensive analysis of total lipid content, and lipid class and fatty acid composition, was used to explore functional diversity and nutritional content within a deep-sea faunal assemblage comprising 139 species from 8 phyla, including the Chordata, Arthropoda, and Cnidaria. A wide range of total lipid content and lipid class composition suggested a diversified set of energy allocation strategies across taxa. Overall, phospholipid was the dominant lipid class. While triacylglycerol was present in most taxa as the main form of energy storage, a few crustaceans, fish, jellyfishes, and corals had higher levels of wax esters/steryl esters instead. Type and amount of energy reserves may reflect dietary sources and environmental conditions for certain deep-sea taxa. Conversely, the composition of fatty acids was less diverse than that of lipid class composition, and large proportions of unsaturated fatty acids were detected, consistent with the growing literature on cold-water species. In addition, levels of unsaturation increased with depth, likely suggesting an adaptive strategy to maintain normal membrane structure and function in species found in deeper waters. Although proportions of n-3 fatty acids were high across all phyla, representatives of the Chordata and Arthropoda were the main reservoirs of these essential nutrients, thus suggesting health benefits to their consumers.

脂质（lipids）是海洋生态系统中的关键化合物，参与生物体的生长、繁殖与存活过程。尽管脂质具有重要的生物学意义且易于检测，但深海研究中对脂质的应用仍较为有限，我们对深海能量与营养流动的认知同样不足。本研究通过对总脂质含量、脂质类群（lipid class）以及脂肪酸组成的综合分析，探究了包含8个门类共139个物种的深海动物群落的功能多样性与营养组成，所涉门类包括脊索动物门（Chordata）、节肢动物门（Arthropoda）与刺胞动物门（Cnidaria）。总脂质含量与脂质类群组成的广泛差异，表明不同分类群间存在多样化的能量分配策略。整体而言，磷脂（phospholipid）是最为主要的脂质类群。尽管三酰甘油（triacylglycerol）是多数分类群的主要能量储存形式，但部分甲壳类、鱼类、水母与珊瑚类群的蜡酯/固醇酯（wax esters/steryl esters）含量更高。部分深海分类群的能量储备类型与含量，或可反映其食物来源与环境条件。与之相反，脂肪酸组成的多样性低于脂质类群组成，且检测到大量不饱和脂肪酸（unsaturated fatty acids），这与当前针对冷水物种的相关研究结论相符。此外，不饱和程度随深度增加而升高，这或表明深海物种存在适应性策略，以维持其细胞膜的正常结构与功能。尽管所有门类的n-3脂肪酸占比均较高，但脊索动物门与节肢动物门的物种是这类必需营养物质的主要储存库，这意味着其捕食者可从中获取健康益处。