Our best estimates suggest that this space is utilized by approxi- 

 mately 700 individual fish. The volume of a cylinder with a radius 

 of 8.5 meters and an average height of 2.0 meters is 454 cubic meters. 

 Substracting 5.3 cubic meters for the reef structure indicates an 

 average density of 1.56 fish per cubic meter. With an average 

 weight of 3.9 grams per fish this suggests a density of 6.05 grams 

 per cubic meter of living space. Similar calculations of the smaller 

 volume in which 75 percent of the fishes' activities take place 

 yields a density of 7 fish (27 grams) per cubic meter. Such average 

 figures, while interesting, tell us little about the actual par- 

 titioning of the available space. For example, the amount of space 

 per individual need not be directly related to the volume required 

 by each individual. The planktivorous Chromis cyanea hovers over 

 the reef usually near the northernmost sea fan but with occasional 

 forays to the rest of the reef and well up into the water column. 

 In the course of an hour each individual probably patrolled a 

 volume of 100 cubic meters but at the same time this space was also 

 utilized by approximately 34 other members of the same species 

 (2.9 cubic meters per fish). On the other hand an individual 

 Pomacentrus may defend territory at the most one meter in diameter 

 and 35 cms deep and because it will not tolerate other individuals 

 of the same species the density is approximately 1 fish per 2 cubic 

 meters. This means that in spite of the greater area required by 

 the Chromis they are using only slightly more space per individual 

 than the sparse Pomacentrus . Column 1, table 1 lists the species 

 recorded from observation reef and the second column lists our best 

 estimates of the numbers of individuals present. 



The third column of table 1 classifies each species as a resident, 

 visitor or transient. Resident species are those represented by 

 individuals that actually live in the area, that is, their home 

 range at least includes the habitat patch under consideration. 

 Whether or not a resident species will be present all of the time 

 depends on the size of the individuals home range. If their home ranges 

 are larger than the habitat patch under consideration there will be 

 part of the time when the individuals are away from the habitat. 

 In other words, continuous presence in the patch is not a necessary 

 criterion of residence. 



Some resident species with home ranges smaller than the reef patch 

 are: Chromis cyanea , C. multilineata , Amblycirrhitus pinos , 

 Pomacentrus planifrons , Pomacentrus partitus , Quisquilius hipoliti , 

 and several other species of gobies and blennies. Species with home 

 ranges that include the observation reef but were larger than the 

 reef area were Epinephelus striatus , Scarus vetula, and adult 

 Canthigaster rostrata . Column 4 table 1 compares our estimates of 

 home range size with the size of the reef patch itself excluding the 

 area of the adjacent sand flat used by the reef residents. 



VI-2G5 



