Invasion, competition, and nonlinear feedback, among others, are phenomena leading to alternating states in complex ecological systems. Changes of regime have profound consequences on the global ecosystem structure and its function, and poses dificult problems for remediation strategies [1,2]. In a class of the above phenomena occurring in lakes and in coastal shallow areas, free floating plants, which are optimal competitors for light, interact with rooted submerged macrophytes, which are effcient in recovering and storing nutrients from the sediments and from the water column. We introduce a model describing nutrient consumption and shadowing effects, with parameters adequate to competition among the rooted seagrass Zostera marina and the macroalga Ulva rigida in coastal areas such as the Thau lagoon (France) or Sacca di Goro (Italy). Successions of dominance states, with different resilience characteristics, are found when changing the input of nutrients and environmental variables.
1. S. Scheffer, S. Carpenter, J.A. Foley, C. Folkes and B. Walker: Nature 313, 591 (2001)
2. S. Scheffer, S. Szabo, A. Gragnani, et al.: PNAS 100, 4040 (2003)