Abstract
Stable isotope analyses, particularly of carbon (δ13C) and nitrogen (δ15N), are used to investigate ecological relationships among species. For marine predators, research has shown the main factors influencing their intra-specific and intra-individual isotopic variation are geographical movements and changes in the composition of diet over time. However, as the differences seen may be the result of changes in the prey items consumed, a change in feeding location or the combination of both, knowledge of the temporal and spatial consistency in the isotopic values of prey becomes crucial for making accurate inferences about predator diets. This study used an abundant marine predator, the Australasian gannet (Morus serrator), as prey sampler to investigate the annual variation in fish and squid prey isotope values over a four-year period (2012–2015) and the geographic variation between two sites with contrasting oceanographic conditions. Significant inter-annual variation was observed in δ13C and/or δ15N values of five of the eight prey species analysed. The strongest inter-annual variation in both δ13C and δ15N values occurred in 2015, which coincided with a strong El Niño-Southern Oscillation (ENSO). This may suggest a temporal fluctuation in the geographic source of prey or the origin of their nutrients. These results suggest that it is important to consider the potential significant differences in isotopic values within the prey assemblages that predators consume. This is important to improve the interpretation of marine predator isotope results when determining the influence of environmental variability on their diets.
Highlights
Stable isotope analyses are powerful tools for understanding the trophic niche of animals and are widely used in ecology, providing important information for conservation [1]
Using an abundant marine predator, the Australasian gannet, as a prey collection agent, the primary objective of the present study was to investigate the temporal and spatial variation in δ13C and δ15N isotopic values in an assemblage of common gannet prey species found in south-eastern Australia
The findings of the present study indicated significant inter-annual variation in both the δ13C and δ15N values of several prey species, suggesting temporal fluctuations in their geographic source or the origin of primary producers supporting prey species
Summary
Stable isotope analyses are powerful tools for understanding the trophic niche of animals and are widely used in ecology, providing important information for conservation [1]. The stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) are commonly used to describe the trophic niche of species [2], to reconstruct animal diets [3, 4], and to make. Temporal isotopic variability of marine prey species to MAR-M (25711 and 31486, respectively). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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