Coupling shell growth and geochemistry in giant clams to explore biomineralization pathways

Marshall-Mills, Kimberley 2024. Coupling shell growth and geochemistry in giant clams to explore biomineralization pathways. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Coral reefs are highly vulnerable to a multitude of global to local stressors associated with human activity and are declining at an alarming rate. In recent years, nearshore turbid coral reefs (light-limited habitats with high sediment input) have emerged as important conservation hotspots due to their potential resilience. They show quick recovery after disturbance and thermal stress and are forecast to play a critical role in the future of marine biodiversity. However, they are understudied compared to their clear water counterparts, with more information needed on how reef-building animals grow calcium carbonate (CaCO3) skeletons in turbid reefs. This thesis explores the intricate biomineralization processes of giant clams (Cardiidae: Tridacninae) across a turbidity gradient in the Coral Triangle region of Sabah, Malaysia. Giant clams are important reef builders facing numerous threats including bleaching and habitat degradation. They also serve as desirable bioarchives, offering insight into past environmental and climactic conditions at high temporal resolution because they grow fast (5–60 μm per day) and live long (>100 years). Herein, I employ and optimize high-resolution imaging and geochemical analysis to disentangle how environmental (e.g. temperature, light availability) and physiological factors interact with shell growth dynamics on turbid reefs. For the first time, the findings herein highlight the significant influence of turbid reefs on shell composition, revealing variation in intra-annual growth, microstructure, crystallographic organization, and element-to-calcium ratios of biominerals. These differences suggest giant clams from turbid reefs are biomechanically superior to low turbid reefs, with implications for their material properties. I hypothesize these changes may be driven by modifications to metabolism, governed by variation in mixotrophic feeding under different turbidity regimes. Overall, this work emphasizes that turbid reefs are key conservation hotspots, potentially shielding giant clams from widespread disturbances. Such insights are crucial for the conservation of reef calcifying organisms amidst anthropogenic change.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Funders:	NERC GW4+ DTP
Date of First Compliant Deposit:	13 May 2024
Last Modified:	13 May 2024 15:56
URI:	https://orca.cardiff.ac.uk/id/eprint/168877

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