Abstract
Dietary studies of marine predators offer an immediate signal of foodweb changes occurring at lower trophic levels, and therefore are often used to assess the ecosystem status of marine systems. Conventionally, these studies are based on morphological analysis of prey remains in stomach contents, involving invasive and destructive techniques to collect samples. More recently, the number of dietary studies based on less invasive biochemical and molecular approaches has dramatically increased. However, all three methods, morphological, biochemical and molecular, have well-documented limitations for resolving taxonomy, temporal variation or biomass composition. In this study, we minimise these limitations by considering multiple techniques in combination. As a case study, we report the target prey species and diet composition of a marine predator that has been used to assess annual change in managed fishing areas for several decades, the macaroni penguin Eudyptes chrysolophus. We use biochemical (stable isotope) and molecular (DNA) analysis of faecal samples collected across the different phases of a single breeding season, and compare the resolved diet to a 26-year dataset of stomach contents collected from a closely located colony (0.25 km apart) that exploits identical foraging grounds. Molecular analysis increased the known target prey species for this highly monitored population by 31%, including a fish species of commercial importance. Biochemical analysis detected subtle changes in the proportion of fish and krill in the diet, demonstrating promising opportunities for using a combined molecular and biochemical method to assess inter-annual foodweb changes at lower trophic levels. The combined approach offers a less invasive sampling methodology, compared to morphological analysis, and provides more information regarding prey species diversity and the overall trophic signature of the diet. Further studies are required to examine the feasibility of using this approach for long-term dietary studies of different marine predator species.
Highlights
Dietary monitoring techniques have been used extensively to examine the predator-prey interactions of species that have an otherwise unobservable lifestyle
The final data set for the 2011/2012 breeding season comprised 40 samples of stomach contents, 29 isotopic analyses of faecal samples, 14 faecal samples analysed by pyrosequencing DNA with fish primers (33% of samples successfully amplified) and 11 faecal samples from pyrosequencing DNA with krill primers (26% of samples successfully amplified) (Table 1)
Unsuccessful amplification of DNA from faecal samples collected during crèche is unlikely to be due to prolonged time in the colony because individuals follow a near diurnal foraging strategy (Williams, 1995), the stable isotope samples for this phase were retained (Table 2)
Summary
Dietary monitoring techniques have been used extensively to examine the predator-prey interactions of species that have an otherwise unobservable lifestyle. For species that exist at the top of relatively short food chains, diet is often used as a proxy for ecosystem status and the availability of target prey species. Such studies are typically based on morphological identification of prey remains in scats or stomach contents (Tollit and Thompson, 1996; Waluda et al, 2012). The number of studies based on molecular techniques, such as DNA sequencing (Jarman et al, 2004; Deagle et al, 2005; Jarman et al, 2013; McInnes et al, 2016), or biochemical markers, such as stable isotope analysis (SIA) and fatty acid signature analysis (Hobson et al, 1997; Iverson et al, 2004), has increased over the past decade. Molecular DNA sequencing of faeces provides a high resolution
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
