C. M. YONGE 



upon corals and extend their shells to keep pace with the growth of 

 these. The final appearance gives a misleading impression of bor- 

 ing. Organisms bore either by mechanical or, if the rock be largely 

 or in part calcareous, by chemical means. The firmer the substrate 

 (e.g. many bivalve shells), the greater the need for at least some 

 chemical assistance in boring. 



Significance and Mode of Boring 



The ability to bore invariably confers a high degree of protection, 

 and this certainly represents the biological reason for the prevalence 

 of the habit. Unlike the wood-boring bivalve Teredinidae (ship- 

 worms) or the crustacean Limnoria (gribble), which obtain much 

 of the energy for boring from the material into which they pene- 

 trate, it is the exception for rock borers to obtain energy in this 

 manner. Nevertheless we may conveniently begin by considering 

 cases where boring is either certainly or possibly associated with 

 feeding. 



Some Association with Nutrition 



Plants. The one certain case where energy is obtained by the 

 borer is that of the fungi which ramify through dead or living bivalve 

 shells, utilizing the energy present in the organic conchiolin matrix 

 of the shell. The best-known instance is provided by the causal agent 

 of Dutch shell disease, which formerly did great damage to Euro- 

 pean stocks of oysters, often spreading as spores to the living oyster 

 shells from dead shells used as a settling surface or "cultch." Korringa 

 (1952) has described the life history; although oysters die if the 

 shells become heavily infected, this is due to reaction by the mollus- 

 can tissues. The fungus itself never penetrates the tissues. Presum- 

 ably boring is along the areas of conchiolin, although some actual 

 penetration of the calcified regions bv either mechanical or, more 

 probably, chemical means may well be necessarv. 



A variety of filamentous green, blue-green, and also some red algae 

 penetrate into calcareous rock or shells, either deeply or superficially. 

 Blue-green algae are abundant between tidal levels on coral reefs, 

 causing a softening which may be due to the action of CO2 or other 



