83' 



26° 



TOTAL SEAGRASS. G M' 



0000 - 0009 

 OOIO - 0090 

 0100 - .0900 



I 



,1000- .9000 

 > .9000 



W^^i^tv 



'^'^^. 



5^. 



. .< 



D .■ ^^ 



26° 



25° 



83° 



82° 



Figure 25. Seagrass export from south Florida to the eastern Gulf of Mexico. In cer- 

 tain areas there is a substantial subsidy to the local carbon and nitrogen budgets by 

 material exported from nearby seagrass beds. 



limit the herbivores responsible for de- 

 tachment (primarily parrotfish, urchins, 

 and turtles). 



Freshly detached, healthy blades of 

 all species float better than senescent 

 ones. Because of the difference in size 

 and shape of turtle grass and manatee 

 grass blades, the effect of direct herbi- 

 vory on the two species is quite differ- 

 ent. When a parrotfish or urchin bites a 



turtle grass blade, 

 only a portion of the 

 attached. However, a 

 is typically only 1 

 one bite severs it, 

 portion to float 

 1979). Similarly, 



it usually removes 

 blade, which remains 

 manatee grass blade 

 to 1.5 mm wide and 

 allowing the upper 



away (Zieman et al . 



green turtles sever 



whole turtle grass blades during initial 

 grazing. 



Because of this difference in re- 

 sponse to grazing, Zieman et al . (1979) 

 found that in Tague Ray 60% to 100% of the 

 daily production of manatee grass was de- 

 tached and exported, whereas only 1% of 

 turtle grass was exported, and this was 

 primarily as bedload. This also indicates 

 the relative successional status of these 

 species. Turtle grass retains more of its 

 leaves within the bed, which thus become 

 part of the litter layer, promoting carbon 

 and nitrogen recycling in the seagrass bed 

 and enhancing its performance as a climax 

 species. By contrast, relatively little 

 of the leaf production of manatee grass is 



79 



