Dr. John Randall (1967) concluded that two factors may hold large 

 plants on a reef in check. One is simply strong competition for 

 a foothold amid the numerous sessile animals; the other, the 

 dramatic influence on the abundance and diversity of plants caused 

 by heavy grazing of numerous plant-eating fishes. Randall reported 

 on the food habits of 212 species of West Indian fishes. More than 

 125 species of red, green-brown and blue-green algae, assorted 

 diatoms and five kinds of aquatic vascular plants were obtained 

 from the stomach contents of 59 species in 16 families of reef fishes. 

 Of these, three families are almost entirely herbivorous, dependent 

 on algae as their primary food. To many others, plants form an 

 important part of the diet. Most fishes are carnivores. The well- 

 known patter - big fish eat little fish, little fish eat lesser fish, 

 lesser fish eat shrimp, shrimp eat "mud" - by and large is true. 

 But In the tropics, and only among several rather highly advanced, 

 recently evolved families of fishes , are there numerous species that 

 tap the bottom of the food chain. 



OBJECTIVE 



Although Randall's work has been extensive, clearly more information 

 is needed on the specific food habits and day-to-day activities of 

 grazing fishes. Taking the standpoint of a botanist, that is, to see 

 how fishes affect the plants instead of visa versa, I began during 

 June 1970 first to survey and catalog the benthic plants in Lameshur 

 Bay, St. John, Virgin Islands, then to concentrate on watching to see 

 what fishes ate what plants, and when, during the 24-hour cycle, the 

 grazers were active. The study was undertaken as a part of Project 

 TEKTITE II Mission 6-50. 



METHODS 



In collaboration with Dr. Arthur Mathieson and Mr. Richard Fralick 

 of TEKTITE Mission 4-50, two 180 m transect lines were established 

 during May 1970 in the vicinity of the TEKTITE habitat. Transect 1 

 was oriented at 240° from the reef near the diving platform and 

 ranged from 12.4 to 18.7 m depth. Transect 2 was oriented at 278° 

 from the reef, due west on the TEKTITE habitat, and ranged from 

 17.3 m to 21.5 m. Wire cages 1.35 mx .6 m x .45 m of 1.3 cm^ 

 mesh were placed at intervals along the lines (Figures 1, 2, 3). 

 The purpose of the cages was to exclude large plant-eating animals 

 in an effort to determine what effect grazing might have on the 

 abundance and diversity of plants in the area. 



During the two weeks of aquanaut- training, June 27 to July 5, I made 

 observations and collections in the Lameshur Bay area using scuba 

 for 23 hours and a rebreather unit for 11 hours in depths to 31 m. 



VI-133 



