Dr Benjamin Walther

Postdoctoral Fellow

Benjamin_Walther

 


ARC Centre of Excellence for Coral Reef Studies, Australian National University

Research Interests
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ANU profile


 


Research Interests

My research generally focuses on using the “natural tag” properties of carbonate hard parts in marine and diadromous fishes to examine dynamics of migration, dispersal, and life history dynamics of species with mobile phases.  This field has grown exponentially in the past couple of decades, yet significant unknowns remain about highly migratory or dispersive species, particularly in the marine environment.  Otolith chemistry has the potential to reveal key information about identity and movement patterns that is essential for the effective management of exploited species and ecosystems. 

My Ph.D. research was on the migratory dynamics of American shad (Alosa sapidissima), a large anadromous clupeid that spawns in freshwater habitats along the Atlantic coast of North America.  I characterized river-specific isotopic and elemental signatures from 20 source rivers and used those to estimate natal homing rates of returning spawners and conduct mixed stock analyses on immature migrants in the ocean.  I will continue work on life history variability in diadromous fishes, and in particular hope to use otolith chemistry to ask questions including 1) are there ontogenetic shifts in oceanic distributions and the degree of mixing among populations and 2) are patterns in habitat use (e.g. movements among fresh and marine habitats) constant or variable among geographically discrete populations. 

A second major area of interest is the degree to which environmental events such as can be detected in chemical signatures of both otoliths and corals in the same locations.  Because Ba/Ca ratios are most abundant in nutrient-rich waters, they can serve as powerful proxies for temporal fluctuations in upwelling or sediment plumes in reef habitats.  I will focus on both comparing incorporation rates of elements in these diverse taxa as well as the consequences of these events for parameters such as growth rates. 

Lastly, I am particularly keen to initiate collaborations among people who use carbonate chemistry as natural tags and those using alternative methods such as genetics, tissue stable isotopes, and satellite telemetry (for example).  I strongly believe the combination of these diverse methods can potentially triangulate questions that would be difficult to answer using only one approach.

 

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