a critical aspect of the community structure. Encounters between 

 individuals of the same and different species are frequent and 

 selection for sharing, rather than competing for, space resources 

 must be intense. 



EQUIPMENT 



The availability of the facilities of the TEKTITE II habitat and in 

 particular the General Electric Mark X rebreather units made it 

 possible to make direct observations of the fishes of a small patch 

 reef during the mission from September 26 to October 11, 1970. The 

 reef (hereafter called observation reef) was selected because of 

 its convenient size - small enough to be studied thoroughly, its 

 general location about 10 minutes swim from the habitat, its 

 isolation from other nearby reefs, and because it appeared to 

 support a rich resident fish fauna. 



PROCEDURES 



Once the reef was located a guide line of bright yellow nylon was laid 

 between the umbilical line and the reef to facilitate our being able 

 to find it with no loss of time, day or night. During the first few 

 observation periods we made sketches and photographed the reef. Base 

 maps sealed between sheets of lucite were then used for notes and to 

 plot the distribution of the fishes on the reef. In the course of the 

 two week period the reef was observed for a total of 41 hours (82 

 manhours) mostly during the daylight hours but sometimes at night and 

 also during morning and evening twilight. 



RESULTS 



Observation reef (fig 1) is a mixed coral patch reef surrounded by a 

 flat sandy open area. Its position is approximately 330 feet northeast 

 of the habitat in water 35 feet deep. Its maximum dimensions are 

 roughly 3 meters by 3 meters. Four smaller reefs were close enough to 

 the main observation reef to be considered with it because fishes 

 were observed to swim back and forth between them and the main reef. 

 Three of these satellite reefs were large Montastrea colonies; the 

 fourth consisted of several species of coral attached to a Diploria 

 colony. The main reef was dominated by helmet shaped and globose 

 Montastrea annularis colonies with other corals including Montastrea 

 cavernosa , Porites astreoides , Porites porites , Diploria stringosa , 

 Diploria labyrinthif ormis , and representative of the general Dichocoenia , 

 Agaricia , Isophyllia and Siderastrea . Several plexaurids were also 

 present. Three large sea fans, Gorgonia sp, , 2 near the north tip and 

 one near the south, formed prominent land marks. Like other sea fans 

 of the area they were oriented with the plane of the body east-west, 

 i.e. perpendicular to the prevailing currents. Other prominent 

 invertebrates were: ophuiroids some of which extended their arms out 

 of small holes at night, sessile clams, tunicates, Diadema sea 



VI-262 



