OBJECTIVES 



The major objectives of the botanical studies of Mission 4-50 were as 

 follows : 



(1) To provide a detailed quantitative evaluation of the 

 species composition, distribution and abundance of 

 the subtidal seaweeds of Great Lameshur Bay. 



(2) To evaluate (in general terms) the effects of fish 

 grazing on seaweed populations around the habitat. 



(3) To compare and contrast the subtidal flora of the 

 Virgin Islands (an area which is well known inter- 

 tidally) with those of New England, where we are 

 presently conducting detailed seasonal observations. 



(4) To compare the efficiency of a surface team and a 

 habitat team while conducting identical work. 



EQUIPMENT 



Metered transect lines, a 200-foot metal tape measure, a 0.6m2 quadrant 

 frame and several metal cages (0.9m x 0.6m x 0.45m and of 1.3cm^ mesh 

 hardware cloth) were employed in the field investigations. A drying oven 

 and an analytical balance were employed (by our support personnel) to 

 determine the dry weight of plant materials. The identification of sea- 

 weeds was made (in the habitat) with a research grade binocular microscope. 



DESCRIPTION OF TRANSECTS AND STUDIES 



Prior to entering the habitat , we made a number of preliminary collec- 

 tions and observations of the subtidal vegetation in the vicinity of 

 Great and Lesser Lameshur Bays, In addition, we established two 180m 

 transect lines in the vicinity of the habitat. The lines were marked off 

 at 3m intervals, and the distance from the reef (designated as zero m) 

 was recorded. The transect lines were held in position by driving pitons 

 into the substrate. Transect 1 was oriented at 240° from the reef near 

 the diving platform. Its depth varied from 12.4 - 18.7m, between 120m to 

 180m was relatively flat (Fig.l). Transect 2 was oriented at 278° from 

 the reef, due west of the habitat. Its depth varied from 17.3 - 21.5m 

 (Fig. 1), Transect 2 showed a more uniform distribution of depths than 1. 

 Both transect lines were established on sandy flat areas (algal plains) 

 below the coral reefs. An area of scattered patch reef was found on both 

 transects from about - 13.5m. Thereafter, only a few isolated coral 

 heads, rocks or shells were present. Table 1 summarizes the composition 

 of the sand grains on transect 2. The substrate was very silty towards 

 the end of the transect. Although it is not illustrated, transect 1 did 

 not show such a gradation. Most of our field work from the habitat was 

 conducted on transect 2. Transect 1 was monitored by two support 

 divers from the surface. The following types of studies were conducted 

 on the transects: 



VI-107 



