B 



Figure 3. --Mean relative aggression level (bites min~l) of threespot damselfish 

 toward urchins on the fore reef (F) and back reef (B) of St. Croix. Fore 

 reef N = 5, back reef N = 10. 



proportion of the Diadema (60.8%) tended to occupy the upper branches of coral 

 ( > 65 cm in height) on the back reef, while 74.5% of the urchins on the fore 

 reef were located on coral branches less than 60 cm above the substrate. 

 Differences in sampling times cannot account for these differences, since all 

 observations but one were made between 1545 and 1830 hr. One back reef 



145 



