Complex Ichnology of the Western Australian Soldier Crab Mictyris occidentalis Unno 2008—The Rosetta Stone to Interpreting Its Population Age Structure and Age-Related Behavior

Abstract

The Western Australian soldier crab, Mictyris occidentalis Unno 2008, presents an unusual association between crab and ichnological features. As the crab progresses through life, its behavior becomes more complex and its ichnological products more varied: from small, sandy clots and pustules, progressing to various types of shallow, pellet-roofed feeding tunnels and then, when emergent and swarming, eruption structures (exit holes), discard feeding pellets, and re-entry rosettes. The size of tunnels, exit holes, pellets, and re-entry rosettes are commensurate with the size of the crabs. The link between crab ichnological product, life stage, and behavior is so direct that its ichnological features can be used as a surrogate to reconstruct population age structure and age-related behavior. In effect, as it progresses through life from being wholly infaunal to alternating infaunal and epifaunal with swarming behavior, autoecologically and palaeoecologically, the ichnology of the Western Australian soldier crab is a “Rosetta Stone” (used metaphorically, for a series of inscriptions on the tidal flat surface) that can be interpreted to determine species occurrence and population age structure, unravel age-related behavior, and, if preserved as ichnofossils, interpret fossil crab sizes, population structures, behavior and palaeoenvironment.

Keywords:

• Crab behavior
• Ichnofossil
• Ichnology
• Mictyris
• Soldier crabs
• Swarming