MEPS 351:287-300 (2007)  -  DOI: https://doi.org/10.3354/meps07174

ABSTRACT: The effects of grazing by the dugong Dugong dugon on benthic invertebrate assemblages in seagrass beds were examined in subtropical Moreton Bay, southeast Queensland, Australia. During feeding, dugongs leave distinct trails through seagrass beds where vegetation has been removed and sediments disturbed. The abundance of benthic fauna was examined along 3 recently created feeding trails and compared to 3 nearby patches of ungrazed seagrass within the same bed. A controlled, manipulative field experiment was then conducted, simulating the effects of dugong grazing, but distinguishing between the effect of removal of vegetation and the disturbance of the sediment during feeding. Dugong grazing was associated with declines in the abundance of benthic animals by up to 85% along trails, with the most noticeable impacts on amphipods and polychaete worms. Simulated dugong grazing caused a significant decline in the biomass of seagrass, through the removal of the vegetation but also from the physical disturbance during feeding. The combined and separate effects on the vegetation and from disturbance were associated with: (1) significant effects of grazing but not of physical disturbance for amphipods, capitellid and opheliid polychaetes; (2) significant effects of physical disturbance with no additional effect of grazing for terebellid polychaetes; (3) significant effects of physical disturbance with an additional effect of grazing for tanaids, bivalves and sabellid polychaetes; (4) significant short-term effects after 1 wk, no longer apparent after 4 wk, for ostracods, nereidid and syllid polychaetes and nemerteans; and (5) no effect of grazing or physical disturbance for isopods and spionid polychaetes.

KEY WORDS: Dugong · Grazing · Subtropical seagrass · Benthic infauna