The Great Isoscape: Using barnacles to retrace oceanic movements

By Dr Ryan Pearson

Techniques for tracking marine animals and objects have long been evolving; gaining in accuracy and reliability. However, most techniques rely on accessing an animal prior to tracking and few techniques are capable of retracing historical movements. Along with conservation efforts for threatened species, marine tragedies (where vehicles disappear in the ocean) are an example of times that recreating the past movement of objects may be particularly useful.

Recently, we have developed and tested a technique that uses barnacles growing on sea turtles to recreate the movement of the host by combining knowledge about growth speeds with chemical analyses of barnacle shells. This technique takes microsamples of shell material and assesses the chemical composition (isotopes) in individual layers of different ages, much like rings in a tree. From this analysis, we can estimate the type of water that the animals were swimming through at different times. Combined with satellite-derived temperature and salinity data, we can then recreate migration pathways, or identify foraging areas that the host animal used, potentially as far back as two years earlier (the approximate maximum age of barnacles on loggerhead sea turtles).

This technique takes microsamples of shell material and assesses the chemical composition (isotopes) in individual layers of different ages, much like rings in a tree.

In our latest paper, we use these techniques to predict isotope values that would be expected from barnacle shells across the entire planet, and at specific times, creating the first ever global maps of barnacle shell isotopes (isoscapes). These isoscapes demonstrate that it may be possible to recreate the movement of any barnacle, and therefore also whatever it was growing on through oceanic waters. The resolution will vary between locations and times of year, but with this knowledge we could expect to derive more precise geolocations for the historic movement of animals and objects than have been possible before. Ultimately, these isoscapes and techniques represent a step forward in better informing conservation efforts and marine forensic investigations globally.

 


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