Seagrass herbivory: evidence for the continued grazing of marine grasses

Unlike the majority of marine plants, seagrasses are believed to experience little damage from the feeding activities of marine herbivores. Based on our previous work, plus a review of the literature, we suggest that this paradigm significantly underestimates the importance of seagrass herbivory in nearshore environments. In this review, we provide evidence from over 100 publications, showing that grazing on seagrasses is widespread in the world's oceans. Overwhelmingly, reports of grazing on seagrasses are based on observations, laboratory measurements, and bioenergetic calculations. To date, few field experiments have been conducted to evaluate the importance of seagrass grazing in the nearshore environment. Of these, even fewer have considered the possibility that herbivores may stimulate rates of primary production of the role of belowground nutrient reserves in determining the impacts of grazers on seagrasses. We contend that the currently accepted view that herbivory plays a minor role in the energetics of seagrass habitats needs to be reexamined by measuring seagrass responses to grazer induced tissue losses in controlled field manipulations. Only then will we be able to determine the importance of the seagrass-grazing pathway in marine food webs.