Patterns of fish and sea urchin grazing on tropical Indo-Pacific seagrass beds

Thalassodendron ciliatum shoots were collected from natural populations of fished and unfished protected seagrass meadows to assess the herbivory of fish and sea urchins. Fish herbivory was restricted to unfished seagrass meadows, while sea urchin herbivory took place in fished as well as unfished areas where fish appeared not to be effective urchin predators. The results of this study confirm that grazing by sea urchins is important in tropical seagrass ecosystems and indicate that herbivorous fish graze, and probably consume, substantial amounts of seagrass production in fishing-protected habitats. The fact that much of the information on seagrass herbivory comes from heavily-fished meadows indicates that large-scale studies, which include unfished areas, are necessary to provide reliable spatial patterns of seagrass grazing distribution.