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

点击翻译按钮获取中文摘要

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.