Ecological interactions and community structure in living and subfossil mollusc assemblages from the southern Great Barrier Reef

Understanding the processes that affect diversity and community structure in environments with little anthropogenic impact is key to validating conservation palaeobiological studies. This thesis investigates how much of the ecology of living molluscan communities can be inferred from dead molluscan assemblages. Ecological and subfossil molluscan assemblages were collected from the One Tree Reef (OTR) lagoon, southern Great Barrier Reef. One Tree Reef has been subject to minimal anthropogenic disturbance, making it well suited to studies linking ecology and palaeobiology. An examination of the living species’ spatial distribution and diversity indicated that neither aggregation nor diversity were different from a random community (Chapter 1). I analysed dead assemblage fidelity and showed that these accurately preserve the living molluscan community (Chapter 2). Observed compositional differences were mainly due to the low probability of sampling rare species, but some taphonomic effects were found (20% of the species). In the last two chapters I provide an in-depth analysis of drilling predation in the OTR lagoon. I initially examined the relation between predator/prey encounter frequencies and predation frequencies (Chapter 3). Then, I examined the effectiveness of individual-level morphological traits previously used in Optimal Foraging experiments as effective defences against drilling predators (Chapter 4). I showed that whileshell size and thickness have a strong explanatory power, species-level differences better predict predation frequency. Therefore, traits typically used to explain predation frequency do not hold their explanatory power at the community level. Overall, by retrieving information from living communities and preserved shell assemblages, I provide new insights into the most studied interaction by palaeobiologists, and show that shell assemblages from a protected reef lagoon are reliable records of past living communities. Confirming dead assemblage fidelity enables us to determine an essential baseline to quantify and remediate changes that marine communities may be subject to in the near future.