Advanced stable isotope analyses of seabird feathers - ecological segregation and historical changes in trophic levels across four Antarctic and subantarctic seabird communities

大量氮和碳稳定同位素分析为研究海洋环境中物种内部和物种间的生态隔离提供了有用的工具，并可以深入了解营养位置和空间分布。然而，在许多情况下，由于缺乏同位素基线数据，对稳定同位素数值的解释受到阻碍。例如，我们现在甚至可以在风暴海燕等小型海鸟的全年海上活动期间跟踪它们，当它们在遥远的水域蜕皮时，它们的羽毛中保存着它们的饮食信息，然后可以在陆地上采样。然而，我们往往无法从那些能够提供同位素基线的遥远水域获得饮食样本。然而，两种先进的稳定同位素技术可以克服这种不足：化合物特异性氨基酸分析(CSIA，由McClelland和Montoya于2002年提出)和氢稳定同位素比率分析(HSIA，由Ostrom等人提出)。2014年)。CSIA的基础是动物不改变某些必需氨基酸(例如苯丙氨酸)，而其他氨基酸在饮食和消费者之间变化很大(例如谷氨酸)。因此，可以根据谷氨酸和苯丙氨酸的氮稳定同位素值的差异来确定营养位置。HSIA被建议作为一种工具来区分由等渗鱿鱼和甲壳类组成的海燕饲料和主要由低渗硬骨鱼组成的海燕饲料。由于等渗和低渗饮食的盐负荷不同，当摄入更多的等渗饮食时，与通过盐腺排盐过程中失水相关的同位素辨别可能导致组织中富氚。本研究的目的是利用这些先进的稳定同位素分析来加强我们对海鸟群落生态隔离的理解。在比较群落研究中，我们将分析南极和亚南极四个海鸟群落的营养结构，重点是小海燕。研究设计提供了独特的可能性，以检验关于生态上相似物种数量不同的群落及其分布不同的物种(冬季分布范围从亚热带到极地)中营养水平分布的假设。此外，我们将分析极地水域中上层海燕摄食生态的年际差异和历史变化：我们将分析之前多年研究中采集的两种海燕物种的羽毛，这些研究涵盖了几个不同食物可获得性的年份，以及几个物种的历史羽毛，可以追溯到大约60-100年前，以调查营养水平的变化。这项研究与战略计划1158的目标一致，特别是通过比较南极和亚南极社区，确定年际和历史变化，并将其与食物供应的变化联系起来，从而确定通往较低纬度的通道，以及对环境变化的反应。

Bulk nitrogen and carbon stable isotope analyses provide a useful tool to investigate ecological segregation within and among species in the marine environment, and can give insights in trophic positions and spatial distribution. However, in many contexts the interpretation of stable isotope values is hampered by a lack of isotopic baseline data. For example, we can now follow even small seabirds such as storm petrels during their year-round movements at sea, and when they moult in distant waters, information on their diet is conserved in their feathers which can then be sampled on land. However, we often cannot obtain diet samples from those distant waters that would provide an isotopic baseline. However, two advanced stable isotope techniques can overcome such shortages: Compound-specific analyses of amino acids (CSIA, proposed in 2002 by McClelland and Montoya) and the analysis of hydrogen stable isotope ratios (HSIA, proposed by Ostrom et al. 2014). CSIA is based on the fact that animals do not change certain essential amino acids (e.g. phenylalanine), while other amino acids change largely between diet and consumer (e.g. glutamic acid). Thus, trophic position can be obtained from the difference in the nitrogen stable isotope values of glutamic acid and phenylalanine. HSIA has been proposed as a tool to distinguish between petrel diets consisting of isosmotic squid and crustaceans and those composed mainly of hyposmotic teleost fish. As salt load differs between isosmotic and hyposmotic diets, isotopic discrimination associated with water loss during salt excretion through salt glands may lead to deuterium-enriched tissues when consuming more isosmotic diets. The aim of the present study is to enhance our understanding of the ecological segregation in seabird communities using these advanced stable isotope analyses. In a comparative community study, we will analyse the trophic structure of four seabird communities from the Antarctic und Sub-Antarctic, with emphasis on small petrels. The study design offers unique possibilities to test hypotheses on the distribution of trophic levels in communities differing in the number of ecologically similar species and among species differing in their distribution (winter distribution ranges from subtropical to polar). Furthermore, we will analyse inter-annual differences and historic changes in the feeding ecology of pelagic petrels in polar waters: We will analyse feathers taken during previous multi-year studies in two petrel species covering several years of different food availability, as well as historical feathers of several species dating back ca. 60-100 years, to investigate changes in trophic levels. This study aligns with the aims of the SPP1158, especially the topics Gateways to lower latitudes - by comparing Antarctic and subantarctic communities - and Response to environmental change - by determining inter-annual and historical changes, and relating them to changes in food availability.