context-dependency in the effects of nutrient loading and consumers on the availability of space in marine rocky environmentscontext-dependency营养负荷的影响和消费者在海洋岩石环境空间的可用性.pdf

Context-Dependency in the Effects of Nutrient Loading and Consumers on the Availability of Space in Marine Rocky Environments 1,2,3 1 1 Fabio Bulleri *, Bayden D. Russell , Sean D. Connell 1 Southern Seas Ecology Laboratories, School of Earth and Environmental Sciences, The University of Adelaide, South Australia, Australia, 2 Dipartimento di Biologia, ` ` Universita di Pisa, CoNISMa, Pisa, Italy, 3 Dipartimento di Scienze Botaniche, Ecologiche e Geologiche, Universita di Sassari, Sassari, Italy Abstract Background: Enhanced nutrient loading and depletion of consumer populations interact to alter the structure of aquatic plant communities. Nonetheless, variation between adjacent habitats in the relative strength of bottom-up (i.e. nutrients) versus top-down (i.e. grazing) forces as determinants of community structure across broad spatial scales remains unexplored. We experimentally assessed the importance of grazing pressure and nutrient availability on the development of macroalgal assemblages and the maintenance of unoccupied space in habitats differing in physical conditions (i.e. intertidal versus subtidal), across regions of contrasting productivity (oligotrophic coasts of South Australia versus the more productive coasts of Eastern Australia). Methodology/Principal findings: In Eastern Australia, grazers were effective in maintaining space free of macroalgae in both intertidal and subtidal habitats, irrespective of nutrient levels. Conversely, in South Australia, grazers could not prevent colonization of space by turf-forming macroalgae in subtidal habitats regardless of nutrients le