Abstract
Biomineralising species will be affected by ocean acidification to varying degrees based on the mineralogical composition of their shells. Lobsters are generally known to precipitate calcium carbonate polymorphs, particularly calcite and magnesian calcite. The inclusion of magnesium into the lattice structure of the calcium carbonate compound increases both strength and solubility, reducing the energy requirements to build resilient shells. A handful of studies have looked at the skeletal composition of lobsters. However, due to the significant phylogenetic differences between sampled individuals, few generalisations can be made. This study focused on Jasus edwardsii (the New Zealand spiny red rock lobster) from Dunedin, New Zealand, a lobster that forms a major marine export from New Zealand with economic and cultural importance within the country. X-ray diffraction was the method used in this study to determine the calcium carbonate polymorph present in the skeleton. Thirteen different body locations were sampled and compared to determine if different body parts produced varying mineralised structures (Chapter 3). There was a large standard deviation among body parts, reducing the degree to which body parts appeared to vary. Attempting to use a non-lethal proxy, moults were sampled to identify the relationship between the whole and discarded shells (Chapter 4). While several body parts were similar, to understand a whole individual, moults cannot be used to identify this relationship in live individuals. While looking at the moults, a spectral peak appeared in the data, which, upon further research, was discovered to be monohydrocalcite (MHC), a hydrated calcium carbonate polymorph, which is the first time this has been noted in crustaceans (Chapter 5). Other than only appearing when Mg-calcite is present, there appears to be no relationship between MHC and any other factor. Within-population in mineralogy was described by comparing individuals to each other (Chapter 6). Two different groups within each population were discovered with moult stage, i.e. pre-moult, intermoult, or post-moult, being proposed to have a significant impact on mineralogy. Among-population variation in mineralogy between Auckland and Dunedin individuals (Chapter 7) showed a similar pattern to within-population dynamics, though latitude (temperature by proxy) appears to have less of an effect thana confounding variable assumed to be moult stage. Jasus edwardsii mineralogically are magnesian calcite and generally high-Mg calcite on average. Further research should determine the moult stage prior to sampling to quantify the effect of this on the mineralogy. It would be recommended to continue to sample the breadth of each individual to add to the dataset to determine the mineralogy of the entire skeleton. Jasus edwardsii are likely to have a long future as an important species for New Zealand, though ocean acidification may have a negative impact on them, due to their observed medium to high magnesium calcite composition of their exoskeleton.