Stable Isotope Dynamics (δ13C and δ15N) in Neritic and Oceanic Waters of the North Atlantic Inferred From GPS-Tracked Cory’s Shearwaters

Filipe R Ceia,Vitor H Paiva,Yves Cherel,Jaime A Ramos

doi:10.3389/fmars.2018.00377

Abstract

Intrinsic markers, such as stable isotopes, are a powerful approach to trace wildlife movements because they do not require initial marking of the organism. The main limitation of the isotopic method is the lack of knowledge in spatio-temporal patterns and dynamics of stable isotopes in marine environments, especially at local scales. Here, we combine GPS-tracks and isotopic signatures from Cory’s shearwaters as a model species to define isoscapes in the North Atlantic, and assess δ13C and δ15N dynamics, from local to regional spatial scales. Tracking data and blood samples were collected seasonally (during pre-laying and chick-rearing periods) across six years (2010-2015) from a total of 191 birds breeding at both neritic and oceanic environments. Tracked birds encompassed a large latitudinal and longitudinal area of the mid-North Atlantic, from the Eastern to Central North Atlantic. Overall, the δ13C and δ15N values of birds’ plasma over the region ranged from -20.2 to -16.2‰, and from 10.8 to 15.5‰, respectively. As expected, strong biogeographic isotopic patterns were found in δ13C values at a regional scale, mostly driven by an inshore/offshore gradient and chlorophyll a concentration. Although a moderate expression of spatial isotopic gradients on δ15N values (i.e. latitudinal and inshore/offshore) in the whole region, these were primarily influenced by temporal drivers (i.e. annual variability). At a local scale (i.e. in a radius of 100 km around the colony, within the neritic environment), both δ13C and δ15N values were very influenced by temporal drivers, suggesting that wide-ranging top consumers are hard to trace locally. This study shows that the δ13C values of marine top consumers are good indicators of the foraging habitat at a regional scale in the mid-North Atlantic, especially in terms of inshore/offshore gradients and areas of higher productivity.

Highlights

Intrinsic markers, such as stable isotopes, are increasingly used to study spatial ecology of individuals and wildlife movements (Bowen, 2010; Ceriani et al, 2014; Quillfeldt et al, 2015)
It should be noticed that temporal drivers had a general significant effect in both δ13C and δ15N values. Both isotopes were very influenced by temporal drivers at a local spatial scale (i.e.,
This study identify relevant relationships between δ13C values and spatial drivers at regional spatial scales, for both neritic and oceanic pelagic environments, emphasizing the relevance of δ13C values for tracing marine life in the North Atlantic

Summary

Introduction

Intrinsic markers, such as stable isotopes, are increasingly used to study spatial ecology of individuals and wildlife movements (Bowen, 2010; Ceriani et al, 2014; Quillfeldt et al, 2015). Isotopic Patterns in the North Atlantic (Hobson et al, 2010; Ramos and González-Solís, 2012) This technique can provide intrinsic tags to study the foraging, migratory and trophic ecology of elusive species, such as marine upper trophic level consumers (e.g., seabirds), and to track the movements of marine lower trophic level species (e.g., fish), and their juvenile stages, that are not amenable to current electronic tagging devices (Graham et al, 2010; MacKenzie et al, 2011; Magozzi et al, 2017). In marine systems, stable isotopes of carbon (13C/12C, δ13C) and nitrogen (15N/14N, δ15N), both at the base of the food web and at the consumer level, typically vary with spatial and physical oceanic features, such as the latitude and the proximity to neritic or benthic habitats (Cherel and Hobson, 2007; Graham et al, 2010). In some instances no major biogeographic gradients and temporal variations were found at a consumer level in regional areas of fairly homogeneous isotopic values (Roscales et al, 2011; Ceia et al, 2015b)

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