Cracking the Shell: An Investigation of Repair in the Oyster, Crassostrea virginica

Date of Award

2019

Degree Name

M.S. in Biology

Department

Department of Biology

Advisor/Chair

Advisor: Karolyn Hansen

Abstract

Biomineralization is a natural phenomenon in which living organisms produce minerals such as bone or shell. This process is widespread across almost all the major phyla, serving various functions in the form of protection, motility, and even digestion. Given the ubiquitous and varied nature of biomineralization, understanding this process poses a challenging task. The bivalve mollusc, Crassostrea virginica, was used as a model organism in this study, as they use biomineralization to create and maintain one of the most important aspects of their existence: shell. Given the fundamental role shell plays, it is necessary to understand how shell formation occurs. Older models of this process suggest a bulk secretion of materials into the extrapallial space; however, this model fails to fully explain how materials are transported to the site of accretion. The research presented here focuses on the potential role of oyster blood, specifically hemolymph, in acting as a transport vector for mineral and organic components. A protein biomarker, the amino acid L-3,4-dihydroxyphenylalanine (L-DOPA), is unique to some proteins involved in rendering the insoluble component of shell organic matrix. Tracking the location and temporal occurrence of these L-DOPA-containing proteins provides insight on how materials are transported for shell formation. An additional component to this study is the characterization of nascent shell after required materials have been transported and incorporated. This research focuses on elucidating the more than decade-old questions concerning shell formation and morphology through the shell deposition process. Three notch-repair studies were conducted to assess short (36 hours), mid (7 days), and long (6 weeks) term changes in materials transport and shell formation. Selected oyster compartments of hemolymph, hemocytes, mantle tissue, and nascent shell were sampled at selected time points to determine the spatial and temporal occurrence of the L-DOPA biomarker as a proxy for proteins involved in shell formation. Results show a consistent increase of L-DOPA-containing proteins in hemolymph from 0 hours to 7 days in the mid-length study. Following a pulse of L-DOPA at one week, a decrease is seen starting at two weeks and reaches a low by six weeks. Along with analyzing oyster blood, microscopic analysis reveals shell growth under normal conditions, results in typical shape and size of crystalline calcium carbonate structures. Shells that have been induced to grow more rapidly have overlapping crystals of more uniform shape and size. Together, these results suggest oyster blood may be acting as transport pathway for delivering materials to the shell formation front and that the rapid deposition of shell in induced oysters is similar in structure and function to normal shell growth.

Keywords

Biology, Ecology, oyster biomineralization, shell formation, Crassostrea virginica, shell material transport, hemolymph involvement in shell repair

Rights Statement

Copyright © 2019, author

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