A critical assessment of marine predator isoscapes within the southern Indian Ocean

Abstract

Background Precise and accurate retrospective geolocation of marine predators via their tissues’ isotopic composition relies on quality reference maps of relevant isotopic gradients (“isoscapes”). Additionally, a good working knowledge of any discrimination factors that may offset a marine predator’s isotopic composition from baseline isotopic values, as well as tissue specific retention rates, are imperative. We provide a critical assessment of inter-specific differences among marine predator-level isoscapes within the Indian Sector of the Southern Ocean. Methods We combined fine-scale GPS tracking data and concurrent blood plasma δ13C and δ15N values of eight seabird species (three albatross, two giant petrel and three penguin species) breeding at Marion Island to produce species- and guild-specific isoscapes. Results Overall, our study revealed latitudinal spatial gradients in both δ13C and δ15N for far-ranging seabirds (albatrosses and giant petrels) as well as inshore-offshore gradients for near-ranging seabirds (penguins). However, at the species level, latitudinal spatial gradients were not reflected in the δ13C and δ15N isoscapes of two and three, respectively, of the five far-ranging species studied. It is therefore important when possible to estimate and apply species-specific isoscapes or have a good understanding of any factors and pathways affecting marine predators’ isotopic composition when estimating the foraging distribution of marine predators via their tissues’ stable isotope compositions. Conclusions Using a multi-species approach, we provide evidence of large and regional scale systematic spatial variability of δ13C and δ15N at the base of the marine food web that propagates through trophic levels and is reflected in the isotopic composition of top predators’ tissues.

Advancing the Sea Ice Hypothesis: Trophic Interactions Among Breeding Pygoscelis Penguins With Divergent Population Trends Throughout the Western Antarctic Peninsula

“…Not surprisingly, Antarctic krill was the dominant prey species provisioned to chicks by all species during each study year (Figure 6A). Interspecific variability in δ 13 C values of penguins has been related to inshore versus offshore foraging habitats of sub-Antarctic penguins (e.g., Carpenter-Kling et al, 2020). We detected relatively little variation in δ 13 C values of chicks across species within each year (Figures 3B-D), which would suggest that adults of all three species are foraging in similar regions while provisioning chicks during the breeding season.…”

Foraging behaviour and habitat-use drives niche segregation in sibling seabird species

“…For ( b ), only two SGP males (green points) made distant trips, and their SEAc could thus not be calculated. Vertical lines in ( b ) show the species-specific δ 13 C values corresponding approximately with the Antarctic Polar Front (PF) and Subtropical Front (SF) [ 75 ]. …”

“…While δ 15 N values are mainly used to indicate the trophic position of animals, they are influenced by differences in baseline δ 15 N values that reflect the isotopic gradients in the Southern Ocean (e.g. [49,75]). These gradients are captured mainly in the δ 13 C values, but when comparing δ 15 N values originating royalsocietypublishing.org/journal/rsos R. Soc.…”

Measurement error models reveal the scale of consumer movements along an isoscape gradient

“…However, linear isoscape gradients are not uncommon in nature and can be found across a wide range of taxa and spatial scales. These include latitudinal (Carpenter‐Kling et al., 2020; Rau et al., 1982), longitudinal (Kurle & McWhorter, 2017; Saupe et al., 1989), and altitudinal (Hultine & Marshall, 2000; Männel et al., 2007) gradients, as well as smaller‐scale freshwater‐seawater (Kahma et al., 2020), coastal‐offshore (Espinasse et al., 2020), and lateral fluvial (Morgan et al., 2009) gradients. As an important caveat, in the present formulation of the MEM the assumption of linearity is critical.…”