Two problems are suggested by these findings. First, why do Cyphoma 

 often leave prey essentially undamaged? Second, in the midst of a 

 superabundant food supply, what prevents Cyphoma from increasing in 

 numbers until they begin to reduce the gorgonacean populations to 

 levels below those which they can efficiently exploit? 



NOTES ON FORAGING STRATEGIES OF CERTAIN CORAL REEF INVERTEBRATES . 



MUREX POMUM 



An interesting defense reaction by the thorny oyster, Spondylus 

 americanus , to Murex pomum was observed. We had tagged and released 

 the Murex at noon on 16 May. At 1000 hours the next morning, Denny 

 Bowman called our attention to the Murex which was attached to the 

 upper valve of the Spondylus . The oyster repeatedly slammed its 

 upper valve open-and-shut onto its lower valve at a rate of 2.5 

 slams/second, while the Murex presumably drilled into the upper 

 valve with its radula. During the next three days, the Murex 

 continued drilling as the oyster continued slamming. At 1945 hours 

 on 20 May, the Murex was found laying upside down at the base of the 

 rock, 8 cm below the Spondylus with its foot stretched upward towards 

 the oyster. A characteristic drill-hole of the muricid was present 

 in the upper valve of the Spondylus . The Murex had repositioned 

 itself on the Spondylus by 1100 hours the following day. The 

 Spondylus was slamming in bursts of up to 10/4 seconds, but these 

 would be followed by periods in which the valves would open and 

 close only 3 times in 45 seconds. The slamming had ceased T?y the 

 following day (22 May) and the Murex had disappeared by noon on 

 23 May, leaving the empty Spondylus shell. We found no signs of 

 drilling by the Murex other than the single hole. 



The capture and ingestion of the oyster (upper valve 6.6 cm long) 

 took the 7.95 cm Murex roughly 6 days. The defense response may have 

 been more effective if the oyster was situated higher on the rock, 

 forcing the Murex to climb further after having been dislodged. 

 Conversely, the ability of the Murex to overcome this defense 

 response appears contingent upon relocating and drilling the same 

 hole when dislodged, rather than starting a new one each time. 



DIADEMA ANTILLARUM 



The sea urchin, Diadema antillarum is an abundant, generalized grazer 

 of plant material and detritus on Caribbean reefs (Randall _et al. , 

 1964). Urchin grazing is probably important in affecting the structure 

 of the benthic community (e.g., algal diversity) in the tropics as 

 it has been shown to be in temperate waters (Kain and Jones, 1965; 

 Leighton _et al^. , 1965; Paine and Vadas, 1970). During a stay in the 



VI-65 



