The common whelk, Buccinum undatum (Neogastropoda: Buccinidae), also known as ‘buckie’ or waved whelk, is a commercially important shellfish species distributed throughout the North Atlantic with over 22,000 tonnes landed in UK waters in 2020, at a value of approximately £27 million. Whelks have no planktonic larval stage, with larvae developing directly in egg cases laid annually by female whelks. Due to this and their limited mobility, whelk populations are often geographically isolated, with a heightened risk of stock depletion and increased concern for conservation and fishery management. 

Whelks are vulnerable to damage from a variety of factors, including feeding, predation, burrowing, mechanical fishery gears and riddling, a process used in the whelk fishery to grade catch by size. Often these incidences of shell damage are recorded as scars on the shell surface following periods of re-growth. Understanding the process(es) involved in shell repair following damage and the consequent recovery mechanisms, is important for the continued sustainability of whelk fisheries. However, there is currently little work into the frequency and degree of shell damage in inshore fisheries, and the mechanisms of repair of the whelk’s shell. This thesis focuses on exploring shell variation and the levels of shell damage seen in whelk populations, whilst identifying factors affecting shell growth and repair, and inspecting shell microstructure and trace element incorporation. Each chapter aims to build on the previous, to create an understanding of the natural variation seen and underlying processes affecting shell growth and repair in this species. 

Initially, a sample of 4000 whelk shells from locations around the UK were assessed (Chapter 2), recording incidences of shell scarring and internal colour, followed by quantitative measurement through spectrophotometry and Raman analysis. The degree of shell damage and variation of internal shell colour were both significantly different between geographic locations, with most whelk shells seeing slight to moderate shell damage, and either a white or brown internal shell colour. 

Having evidenced that damage and re-growth of the shell occurs, a series of experimental damages were carried out using live tank-reared and wild-caught whelk held in laboratory-controlled conditions (Chapter 3). In whelks with experimentally-damaged shells significant differences in the rate of  shell growth and repair were observed when investigating life stage, temperature, and season. For experiments of feeding regime, significant differences were only found for total shell growth, and for sex, significant differences were only found for shell repair rates. Nonetheless, for all experiments, shell damage did not significantly affect the rate of total shell growth. Through the characterisation of these biological and environmental factors, this chapter demonstrates that there are multiple factors controlling shell growth and repair rates. 

Shells of these whelks were then prepared to assess the original and repaired sections using scanning electron microscopy (SEM) and X-ray diffraction (µXRD) for structural assessment (Chapter 4) and X-ray fluorescence (µXRF), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and extended X-ray absorption fine structure (µEXAFS) for trace element analysis (Chapter 5). These data confirmed whelk shells to be fully aragonitic and established they are formed of only two distinct microstructures; prismatic and crossed lamellar. Inert-element bond lengths and trace element incorporations were consistent within a shell layer, including into new growth, however for trace element incorporation higher concentrations of Mg, Sr and Ba were seen in the outer prismatic layers. 

Through the combined findings of this thesis, insight has been gained into the variability in shell structure of the whelk, whilst establishing underlying causes for changes in rates of shell growth and repair. These findings will help feed into fisheries research, where current management plans require an increased understanding of this data-poor commercial species. Through improvements in the understanding of the controls on shell growth and shell damage and the frequency of shell repair, it will be easier to sustainably manage these stocks.