EXTRACTION OF ENVIRONMENTAL 



INFORMATION STORED 



IN MOLLUSCAN SHELLS: 



APPLICATION TO ECOLOGICAL PROBLEMS 



Donald C. Rhoads and Richard A. Lutz 



Department of Geology and Geophysics 



Yale University 



New Haven, Connecticut 06520 



ABSTRACT 



Ecological stress, when broadly defined, is responsible for most, if not all, 

 growth patterns within the molluscan shell. As the type of pattern deposited is 

 largely a function of the specific biological or environmental stress involved, 

 considerable ecological information is stored within the exoskeleton. The 

 resulting record is in the form of either (1) microstructural growth increment 

 sequences or (2) cha^nges in the shell structural type (e.g., nacreous, prismatic, 

 CTOssed-lamellar, etc.) or relative proportions of structures within the shell. 



Microstructural growth increments, heretofore interpreted as resulting from 

 varible despositional rates of calcium carbonate and organic matrix, are viewed 

 as refections of periodic shell dissolution-deposition cycles. 



Changes in the type of crystalline structure deposited under various 

 environmental conditions within the inner shell layer of several species of 

 bivalves have been defined. During periods of extreme ecological stress, such as 

 prolonged exposure to sub-freezing temperatures, extensive dissolution and 

 "reworking" of this inner layer occurs in a number of species. 



Extraction of environmental information recorded within the shell is 

 facilitated through examination of polished thin sections, acetate peels, 

 fractured shells, polished and etched shell sections, and growth surfaces using 

 polarizing, optical, and scanning (and, occasionally, transmission) electron 

 microscopy. Application of these techniques to long-term monitoring of 

 ecologically stressed environments is discussed. 



INTRODUCTION 



Ecology has been defined as the study of relationships between organisms 

 and their environment (28). In functioning ecosystems it is possible to make 

 direct observations of these relationsliips in real time. Organism-environment 



157 



