Seagrasses grazing

LeafN content is an important determinant of food preference and the quantity of seagrass material consumed for some herbivores. Several field and laboratory studies have found a positive relationship between leaf N content and grazing by parrotfish, turtles and dugongs (e.g., Goecker et al, 2005 McGlathery, 1995 ... 

Given the relatively low assimilation efficiency of most herbivores, little of the ingested leaf and epiphyte material will remain in consumer biomass. Most will be egested as feces or soluble compounds and will be remineralized. This suggests that where grazing is an important fate for seagrass material, most of the N bound in the plant material will be transferred to the decomposers. If the grazers are mobile, a portion of this N may be lost from the system (Preen, 1995). 

Figure 23.2 Conceptual model showing the possible fates of seagrass-hound nitrogen. Nitrogen temporarily immobilized in plant tissue can become available through exudation from live tissue, remineralization through decomposition, and grazing and subsequent excretion. Some material may be removed from the system through burial or export as dissolved or particulate organic matter.

McGlathery, K. J. (1995). Nutrient and grazing influences on a subtropical seagrass community. Mar. Ecol. Prog. Ser. 122, 239-252. 

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