DAME: ALLOMETRIC RELATIONSHIPS IN OYSTERS 



LENGTH 



1.00 



0.10 



0.02 — 



I I I I I 



HEIGHT 



Figure 4. — The fitted allometric curves for the dry body 

 weight/height and dry body weight/length relationships 

 for intertidal (I) and sub tidal (S) oysters. 



from different measurements depends on sig- 

 nificantly different models for the intertidal- and 

 subtidal-zone oysters. 



The shell weight/dry body weight ratio for 

 Crassostrea virginica at North Inlet is signifi- 

 cantly higher in subtidal oysters than in inter- 

 tidal oysters. This observation supports the 

 general observation of Galtsoff (1964) that the 

 shells of intertidal oysters are usually thinner 

 than those of subtidal oysters. The higher shell 

 weight/dry body weight ratio for subtidal versus 

 intertidal oysters is substantiated by the findings 

 of Wilbur and Jodrey (1952), who showed that 

 the amount of shell deposited by C. virginica was 



directly proportional to the time exposed to sea 

 water. Rao (1953), observing a similar rela- 

 tionship between intertidal and subtidal Mytilus 

 edulis and M. calif ornianus, believed that the 

 deposition of calcium by molluscs is directly de- 

 pendent on the amount of time the animal is sub- 

 merged. Baird and Drinnan (1957), finding a 

 lower ratio of shell weight/dry body weight 

 in subtidal M. edulis than in intertidal mussels 

 of the same species, suggested that closed, ex- 

 posed animals undergo anerobic metabolism 

 which reduces body tissues more rapidly than 

 chemical erosion of the shell. Lent (1957), dis- 

 covering no differences in the shell weight/dry 

 body weight ratio for the mussel Modiolus de- 

 missus from diflferent tidal levels, attributed the 

 result to the air-gaping phenomenon exhibited 

 by Modiolus, which allows this organism to con- 

 tinue aerobic metabolism in both the submerged 

 and exposed states. At present, it is doubtful 

 if a general statement can be made that will re- 

 solve the different hypotheses. Thus, one might 

 speculate that local environmental conditions 

 such as tidal range, wave action, and water 

 chemistry may be important in determining 

 shell weight/dry body weight ratios. 



In this study, the percentage water in the tis- 

 sues, as calculated from the dry body weight/soft 

 body weight relationship, falls within the re- 

 ported range of 75-88% for Crassostrea virgin- 

 ica (Galtsoff, 1964). Intertidal oysters appear 

 to retain a significantly higher proportion of 

 their body water than subtidal oysters. The 

 higher retention of water in intertidal oysters 

 may result from some form of physiological 

 adaptation to the intertidal environment, such 

 as an increased ability to remain closed when 

 they are exposed. 



The relationships of dry body weight/whole 

 body weight, dry body weight/height, and dry 

 body weight/length are all different for inter- 

 tidal and subtidal oysters, but there appears to 

 be no obvious biological reason to explain these 

 differences. It may simply be that any differ- 

 ences in dry body weight for intertidal and sub- 

 tidal oysters are translated into differences in 

 allometric relationships. 



Galtsoff (1964) has noted that the condition 

 index (dry body weight/ volume of shell cavity 



1125 



