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) changes in the shell structural type (e.g., nacreous, prismatic, 
crossed-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 relationships in real time. Organism-environment 
157 
