Recognizing Incipient Epizootic Shell Disease Lesions in the Carapace of the American Lobster, Homarus americanus Running title: Recognizing Incipient Epizootic Shell Disease in American Lobster

Causal factors leading to Epizootic Shell Disease (ESD) lesions in American Lobster, Homarus americanus, are still not well understood. We explore the structural and physiological bases for development of ESD to early visible stages from earlier stages invisible to unaided eye. We suggest a lobster shell model which develops structural functional vulnerability and explains the origin of ESD. Medallions of carapace cuticle are obtained from carapace fixed with various protocols to minimize movement of mineral and macromolecular components. Minimal processing of medallions is used to encourage large sample sizes compatible with environmental surveys. Oneand two-dimensional analytic maps of polished sections of the cuticle, obtained with an Electron Microprobe, describe the composite mineral and polymeric structures. MicroRaman Spectroscopy identifies bonding types of phosphates and carbonates as well as signatures of organic structures. The frequency and properties of identified structures can be monitored through the lobster molting cycle using high throughput application of microComputed Tomography (μCT) to quantify the frequency of structures of interest. We observed density differences in the calcite layer, inner exocuticle and endocuticle and the frequency and structure of CaCO3 structures in the endocuticle and membranous layer of carapace cuticle during stages of the molting cycle. The correlative microscopy and μCT of shell structures will lead to an improved understanding of the lobster cuticle structure. Detailed structural differences quantified though development and under different environmental conditions can provide insight into causes and vulnerabilities associated with ESD.