HIRTH, KLIKOFF, and HARPER: SEA GRASSES AT KHOR UMAIRA 



400 n 



u. 350 



cr 



<i 



° 300 



X 



cr 



250- 



200- 



150 



100- 



50- 



Y = I0.4 +2 8X 

 r = .90 



10 20 30 40 50 60 

 PERCENT COVER 



70 80 90 100 



Figure 2. — Above-ground dry weight of Cymodocea 

 serrulata regressed on field estimates of plant cover made 

 at Khor Umaira. 



analyzed was a composite of five samples taken 

 at a depth of 0-2.5 cm. The pH was obtained 

 using a glass electrode, particle size was based 

 on material passing a 2-mm sieve, and the other 

 chemical parameters were determined using 

 standard soil testing techniques. The results are 

 as follows: pH 7.2; sand 97% ; silt 3% ; clay 0% ; 

 phosphorus 0.027 mg/g substrate; calcium 73.5 

 mg/g substrate. 



The regression lines in Figures 2 and 3 show 

 that given equal cover, standing crop is greater 

 in a mixed pasture of Cymodocea and Syriiigod- 

 inni than in a homogeneous stand of Cymodocea. 

 This may be due to the close packing of the 

 terete leaves of Syriitgodium in the mixed 

 pasture. 



The caloric content of four genera of sea 

 grasses collected in the bay at Khor Umaira and 

 one genus ( Thalassodendroii ) collected off the 

 nearby coast at a depth of 4.5 m, are given in 

 Table 1. The data show that the caloric content 

 of the five genera are very similar. 



The standing crop of an equally mixed pasture 

 of C. serrulata and S. isoetifolium at Khor 

 Umaira can be obtained from cover estimates in 

 Figure 3. Leaf blades of both species here were 

 less than 20 cm. On the average, water amounted 

 to 88.7% of the wet weight of the leaves (range 

 83-91%). 



In order to determine some chemical param- 

 eters associated with dense sea grass pasture, 

 water samples were collected just above the 

 leaves of an equally mixed stand of C. serrulata 

 and S. isoetifolium with 100% cover at a depth 

 of 1.75 m (at low tide) at 0915 h on 30 July 1972. 

 The pH was determined using colorimetric stan- 

 dards and the other chemical parameters were 

 obtained using standard methods for water anal- 

 yses. The results are as follows: temperature 

 29.2°C; salinity 36.50"/oo; chlorinity 20.19"/oo; 

 pH 8.2; free carbon dioxide 10 ppm; dissolved 

 oxygen 5 ppm; total alkalinity 122 ppm, with 

 36 ppm as carbonate alkalinity and 86 ppm as 

 bicarbonate alkalinity; magnesium chloride 

 4,000 ppm; and calcium chloride 999 ppm. 



Substrate samples were taken at the same 

 site and at the same time as the water samples. 

 The substrate of this site consists largely of 

 coarse fragments of shells. The bottom sample 





X 

 (J 



CE 



O 



< 



500i 



450' 



400- 



350 



300- 



250 



200 



150- 



100- 



50 



Y = 42 + 3 9X 

 r =90 



I 1 I I 



20 30 40 50 



PERCENT COVER 



— p— 

 60 



— r~ 

 70 



80 



90 100 



Figure 3. — Dry weight of a stand consisting of equal 

 quantities of Cyniodoceu serruUiia and Syriiiiiodiuiu 

 isoetifolium regressed on field estimates of plant cover. 

 All data are from Khor Umaira and include only above- 

 ground tissue. 



1095 



