Behaviour, Social Structure and Population Genetics of the Burrowing Shrimp, <i>Trypaea australiensis</i>

<p dir="ltr">Burrowing shrimp, such as <i>Trypaea australiensis </i>(Decapoda, Axiidea, Callianassidae), play vital ecological roles as ecosystem engineers by modifying sediment structure and water quality through their burrowing activities. These alterations affect a wide range of organisms, from microorganisms to larger fauna and flora. Despite their ecological importance and widespread use as bait in recreational and commercial fisheries, their behaviour, social systems, and population dynamics remain poorly understood due to their cryptic lifestyles. This knowledge gap not only raises concerns about potential overexploitation but also hinders the development of effective conservation and management strategies. This thesis investigates the social structure, burrowing behaviour, and population genetics of <i>T. australiensis</i>. Our findings from field surveys revealed diverse social structures, with individuals primarily solitary but also forming pairs (including same-sex and opposite-sex pairs) and sometimes groups, with social structure being influenced by body size, seasonality, and location. To further exploration social behaviours and enable comparisons with field data, we conducted manipulative experiments at the Ecological Research Centre (ERC) at the University of Wollongong, where conspecifics of both sexes were introduced into the burrow of a resident shrimp. These laboratory manipulations revealing greater tolerance for opposite-sex individuals, albeit temporarily. In another laboratory experiment, we explored the likely mechanism by which shrimp formed pairings by allowing 2 shrimp to simultaneously burrow within the same aquaria. These shrimp were found to connect their burrows when in proximity to a neighbouring shrimp and more frequently did so when they were of opposite sex. Additionally, burrow structure was assessed using field-collected resin casts, 3D scanning and laboratory behavioural observations of solitary shrimp. Burrow morphology through resin casts indicated variations in depth and complexity between sites, while laboratory observations showed that shrimp dedicate significant time to burrow maintenance. Finally, genetic analysis using SNP markers across three locations indicated no significant population structure, suggesting high gene flow and providing crucial preliminary population genetic data for <i>T. australiensis </i>that supports management of <i>T. australiensis </i>as a single unit. All in all, this thesis provides new insights into the social and burrowing behaviours of a key cryptic species. The results underscore the ecological significance of burrow habitats and highlight the need for further research on cryptic invertebrates to guide effective conservation and fisheries management.</p>