Unique Post-telemetry Recapture Enables Development of Multi-Element Isoscapes From Barnacle Shell for Retracing Host Movement

Ryan M Pearson,Rod M Connolly,Jason P Van De Merwe,Michael K Gagan

doi:10.3389/fmars.2020.00596

Abstract

Many ecological investigations rely on understanding the movement of animals through marine environments. Most available tracking techniques are invasive (e.g., tissue sampling) and require extensive effort and/or cost (e.g., capture-mark-recapture or satellite telemetry). The isotopic compositions of barnacle shells (delta C-13 and delta O-18) are known to record the ambient water temperature and salinity conditions in which they grew. Thus, isotopic analysis of barnacles on animals or objects has the potential to yield information about their movement between water bodies of varying isotopic properties. We present, for the first time, isotopic data for barnacle shell samples that grew on a satellite-tracked sea turtle host. The satellite telemetry record, together with documented barnacle growth rates, allowed for sequential samples from individual barnacle shells to be assigned a specific time and location for direct comparison of isotope values to environmental conditions. We developed models that allow barnacle shell delta C-13 and delta O-18 to be linked, with a high degree of predictability, to sea surface temperature (SST) and salinity (SSS). Our sea turtle case study demonstrated how these models can be used to create isoscapes, allowing hosts to be tracked in space and time at higher resolution than most attempts to use soft-tissue isotopes for a similar purpose, and at considerably lower cost than satellite telemetry. The conceptual advance presented here could be applied widely to understand the movement of any animal or object that carries hitchhiking barnacles.

Highlights

Conservation efforts for threatened taxa generally rely, to some extent, on understanding the movement and habitat use of target species (e.g., Scott et al, 2012; Mazor et al, 2016)
SSS was highest nearer the southern end of the migration (35.2 PSU where the second sample was formed) and lowest (33.9 PSU) in the vicinity of the recapture location (Figure 2)
We describe the relationship between SSS and δ18Osw values in NW Australia using δ18Osw values calculated via the balanomorph barnacle paleotemperature equation (BBPE)

Summary

Introduction

Conservation efforts for threatened taxa generally rely, to some extent, on understanding the movement and habitat use of target species (e.g., Scott et al, 2012; Mazor et al, 2016). Recent decades have seen an increase in the use of isotope analyzes for these purposes (e.g., Vander Zanden et al, 2015; Peavey et al, 2017; Fleming et al, 2018; Marcus et al, 2019). Studies of this nature have predominantly focused on analysis of the tissues of the animals themselves. Barnacle analyses limit the need for invasive sampling procedures on threatened animals and opens potential new lines of investigation, including hindcasting of the movement of anything that carries hitchhiking barnacles

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Conclusion