The Role of Novel Mineralization in the Structural Integrity of the Lobster Cuticle

Joseph G. Kunkel
Biology Department
UMass Amherst
- and -
Professor Sabine Hild
Johanes Kepler U.
Linz, Austria

The lobster exoskeleton is being used as a model of a mineral plus organic polymer composite material. This material is currently under attack in nature by a number of diseases which threaten the commercial value of the lobster. Empoundment Shell Disease and Epizootic Shell Disease both create lesions in the American lobster cuticle which look unsightly, especially when the lobster is boiled to produce the expected bright red shell. These lesions involve an erosion of the mineral and organic fiber of the cuticle as well as deposition of a melanic defensive wall which is seen as brown to black against the normal red of the cooked lobster.

We are examining the mineral properties of the cuticle which usually present an impervious barrier to microbial attack. The minerals which we are studying include the usual calcite crystaline form of calcium carbonate which we see providing a tight surface barrier to microbes plus a putative novel compound for animal tissues, tetraclcium phosphate (TTCP) which we propose is used to line the canals that carry secretions and neurons across the normal intermolt lobster cuticle. This proposed crystal structure would have very favorable properties for protecting the lobster from acid attack by bacteria which enter the canals at the surface of the lobster cuticle. We propose using the FTIR approach, with which Professor Hild, has expertise to examine this structure to examine whether it has the proposed TTCP structure. In addition we will examine an additional phosphatidic trabecular structure which looks to be a mixture of an amorphous calcium carbonate with an as yet unidentified phosphatidic compound. Again FTIR promises to allow us to tease apart the components of the structure and allow us to identify the phosphatidic compound. The trabecular structure is possibly the unique architectural design which gives the lobster cuticle its rigid structure. Examining this feature may provide clues to how nature has produced the stucture which has provided the structural rigidity that has served the lobster well for eons. These studies may also provide clues to what is failing during the shell diseases which we are observing in natural and aquacultured populations.

Dr. Kunkel will be able to bring the sample collection and sample preparation protocols that he has developed in his Amherst MA laboratory to collaborate with the material science technology that Dr. Hild has developed in her laboratory.

We expect this collaboration to result in a new understanding of the ancient composite material which may allow us to design new composite materials with improved properties. The lobster cuticle may be responding adversely to changes in the oceans and aquaculture conditions that many not be easily reversed in nature. Acidification and warming trends may make the present design of a calcium carbonate cuticle vulnerable. If we can understand such vulnerablility we may be able to suggest ammendments to current aquaculture practice or environmental regulations which might ameliorate the effects. In addition, if we understand the vulnerability we may be able to design artificial composites without those vulnerabilities.