Similarly, following short-term or low levels of sedimentation, structural (i.e. polyp re-colonization) (Wesseling et al., 1999) and functional (i.e. photosynthetic activity) (Philipp and Fabricius, 2003) recovery within days to weeks has been demonstrated for some, but not all, coral species. Coral growth recovered within weeks following short-term enrichment of N, and of PI3K inhibitor drugs N and P combined, but not of P (Ferrier-Pages et al., 2000). It is unlikely for such swift recovery to occur following restoration of more natural freshwater, sediment

and nutrient fluxes, given that coral ecosystem processes would have been chronically impacted for years to decades, if not centuries. The well-known case of Kane’ohe Bay, Hawaii, is the only example demonstrating partial reversal of coral reef degradation following a reduction in terrestrial nutrient fluxes. Following sewage diversion in 1978, turbidity, nutrients and chlorophyll a concentrations, as well as macroalgae biomass, declined within months ( Laws and Allen, 1996 and Smith et al., 1981). In the next few decades, coral cover more than doubled and subsequently

stabilized, however, further recovery may at least be partly constrained by nutrient sources other than sewage outfalls, by modified freshwater and sediment fluxes resulting from historical and recent changes in the Bay and its catchments ( Hunter and Evans, 1995), and by additional impacts of introduced macroalgae

( Conklin and Smith, 2005). To reverse coral reef degradation, Afatinib chemical structure it is critical to define the different ecosystem states of a coral reef system, and understand the ecological processes that drive the change from one state to another. This relates to the concept of resilience, i.e. the capacity of an ecosystem to absorb perturbations before it shifts to an alternative state with different species composition, structure, processes and functions (Folke et al., 2004). For coral reefs, multiple alternative states can exist and have been documented for coral reefs, generally dominated by organisms other than reef-building coral (Gardner et al., 2003, Hughes et al., 2010 and Mumby et al., 2007). Chronic environmental pressures such as changes in terrestrial fluxes of freshwater, sediment, and nutrients (De’ath and Fabricius, Myosin 2010, Dubinsky and Stambler, 1996 and Fabricius, 2011) reduce resilience by decreasing the threshold at which the coral-dominated state shifts into a different state. A return to the more desirable coral-reef dominated state by reducing chronic drivers of change such as land-based pollution may be difficult to achieve due to the inherent stability of the degraded state, known as hysteresis (Mumby and Steneck, 2011). We identified multiple examples in the global literature where reductions of land-based pollution to coastal ecosystems have been achieved (Table 2).