Ichnological Studies of the Western Australian Soldier Crab Myctyris Occidentalis Unno 2008: Correlations of Field and Aquarium Observations
Royal Society of Western Australia
Place of Publication
Faculty of Computing, Health and Science
School of Natural Sciences / Centre for Ecosystem Management
The Western Australian soldier crab, Mictyris occidentalis Unno, spends most of its life cycle in- faunal in sandy tidal environments, and produces up to 16 different types of ichnological products: back-filled burrows, cavities, circular pustular structures, clots, craters, dactyl prints, discard pellets, eruption structures, excavation pellets, exit holes, hollow shafts, linear pustular structures, mat pustular structures, rosettes, scrape marks, and surface-parallel tunnels (with their floors and roofs). These are the result of the crabs working the sediment at different stages of their life cycle, whether or not they emerge, and their working of the sediment at different times of the tide. Soldier crabs have three phases to their ichnological behaviour corresponding to their life stages. Newly arrived recruits and juvenile crabs are cryptic, and develop sediment surfaces strewn with clots. Crabs in the early to middle stage of their life cycle also are cryptic, and develop subsurface cavities during high water, and subsurface cavities and sediment surfaces covered in pustular structures during low water. Adult crabs exhibit cryptic and emergent phases, and develop the most complex range of ichnological products - during high water, they form subsurface cavities, and during low water they develop cavities in the subsurface as well as sediment surfaces covered in pustular structures, exit holes, dactyl prints (sometimes), discard pellets, and rosettes. Mapping of crab activity and the boundaries of their workings at various scales shows there was a variability in crab behaviour as to whether adult crabs emerged or not, whether working of the sediment surface took place, where in the population emergences or subsurface workings took place, and in the subsurface whether the crabs were active or inactive. Similar variability in crab behaviour was observed in the aquarium. Our study showed a direct correlation between field and aquarium ichnological patterns, and the aquarium observations provided explanation of the field results.