Grazing by all members of an herbivore community can act to structure the ecosystems they feed on. The outcome of this grazing pressure on the plant community also depends on the interaction between different herbivore groups that are present. We carried out a three-month multi-level field exclusion experiment to understand how different groups of herbivores act both individually and interactively to structure a subtropical seagrass meadow in the Great Barrier Reef. Megaherbivore grazing had the largest impact on this seagrass meadow, significantly reducing aboveground biomass and shoot height, whereas there was no measurable impact of meso- or macroherbivores on seagrass metrics or epiphyte biomass. Megaherbivores here grazed broadly across the meadow instead of targeting grazing in one area. The principal seagrass-herbivore dynamic in this meadow is that megaherbivores are the main group modifying meadow structure, and other grazer groups that are present in lower numbers do not individually or interactively structure the meadow. We demonstrate that herbivory by large grazers can significantly modify seagrass meadow characteristics. This has important implications when designing and interpreting the results of monitoring programs that seek to conserve seagrass meadows, the ecosystem services that they provide and the herbivores that rely on them. Collectively, our results and those of similar previous studies emphasize there is unlikely to be one seagrass and herbivory paradigm. Instead, for individual meadows, their unique species interactions and differences in biotic and abiotic drivers of seagrass change are likely to have a strong influence on the dominant seagrass-herbivore dynamic.

食草动物群落的所有成员都可以放牧，以构成其赖以生存的生态系统。放牧压力对植物群落的影响还取决于存在的不同草食动物群体之间的相互作用。我们进行了为期三个月的多层次野外排除实验，以了解不同种类的草食动物在大堡礁中如何单独地和交互地构造亚热带海草草甸。食草性食草动物对该海草草甸的影响最大，大大降低了地上生物量和枝条高度，而中，大型食草动物对海草指标或附生生物量没有可衡量的影响。这里的大型食草动物在草地上广泛放牧，而不是在一个地区放牧。该草地的主要海草-草食动物动态是，大型食草动物是改变草地结构的主要群体，而其他数量较少的放牧者群体则不会单独或交互地构成草地。我们证明大型放牧者的食草性可以显着改变海草草甸的特征。这在设计和解释旨在保护海草草甸的监测计划的结果，其提供的生态系统服务以及依靠它们的食草动物时具有重要的意义。总的来说，我们的结果和先前类似研究的结果都强调，不可能有一种海草和草食动物范式。相反，对于单个草地，