Impact of dugong grazing and turtle cropping on tropical seagrass communities

Abstract

The impact of grazing by two megaherbivores, the Dugong Dugong dugon and the Green Turtle Chelonia mydas on the community structure of intertidal seagrasses was investigated experimentally over two time frames (shorterterm: 1-4 months; longer-term: 10 and 13 months), at three levels of grazing intensity (leaf cropping, light grazing, intensive grazing), at two seagrass meadows in tropical Queensland, Australia: (1) a mixed species bed of Zostera capricorni, Halophila ovalis, Halodule uninervis, Cymodocea rotundata and Cymodocea serrulata, and (2) a monospecific bed of Halodule uninervis. From the perspective of the megaherbivores, grazing improved the structure and dynamics of the tropical seagrass communities by altering their biomass, volume of detritus, net aboveground biomass productivity and the species composition of the mixed-species bed, Recovery from grazing disturbance occurred after several months to a year.