Crustacean Age Determination Using Ossicular Growth Records: Southern Synthesis

Direct age determination of decapod crustaceans is now possible.  Here we demonstrate the utility of direct-aging methods using a subtropical freshwater crayfish model (redclaw, Cherax quadricarinatus), before presenting the preliminary findings for other commercially-important Australian crustaceans.  C. quadricarinatus ossicles are not molted and contain growth marks that are suitable for age determination.  We provide an evidence-based protocol for our count origin and demonstrate that growth marks counts are repeatable.  The von Bertalanffy growth model was used to describe C. quadricarinatus growth.  The maximum C. quadricarinatus age (3+) was not indicative of molt history, but aligned closely with indirectly-obtained longevity information.  Calcein retention over an annual cycle confirmed that ossicles record past events.  The subsequent deposition of an apparently complete annual cycle (in one individual) provided evidence for annual periodicity, but further research is needed for a definitive validation.  Preliminary findings for a range of subtropical and temperate Australian species (e.g. eastern rock lobster, Sagmariasus verreauxi and Tasmanian giant crab, Pseudocarcinus gigas) are presented, including growth modelling, age validation techniques (i.e. calcein staining and laser ablation) and method verification (using known-age individuals).  We discuss recent aging advances and challenges, with a view towards stimulating research collaborations and identifying future research priorities.