MEPS 124:201-213 (1995)  -  doi:10.3354/meps124201

Impacts of dugong foraging on seagrass habitats: observational and experimental evidence for cultivation grazing

Preen A

In Moreton Bay, Australia, dugongs (Dugong dugon) often graze in large herds at the same location for weeks to months. Such grazing reduced seagrass shoot density by 65 to 95%, aboveground biomass by 73 to 96% and belowground biomass by 31 to 71% at 3 sites ranging in size from 2 to 75 ha. Following even the most intense and sustained grazing, the space between surviving tufts of seagrass remains small (<1 m2) and recovery is usually rapid (months). In this regard, intensive grazing differs from disturbances caused by storms, sedimentation or disease. However, recovery of seagrass meadows can be suppressed by low levels of sustained grazing pressure. The species composition of seagrass meadows can be altered by intensive grazing, which favours rapidly growing, early pioneer species, such as Halophila ovalis, at the expense of slower growing but dominant species such as Zostera capricorni. In Moreton Bay, H. ovalis is the most nutritious (high nitrogen, low fibre) and the most preferred seagrass grazed by dugongs. Z. capricorni is the least preferred species. By preventing the expansion of Z. capricorni and increasing the abundance of H. ovalis, this grazing system, termed cultivation grazing, can improve the quality of the dugong's diet.


Cultivation grazing . Seagrasses . Dugongs


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