Figure 1

Model simulations of seagrass density Z (shoots m⁻²), sulfide concentrations S (µmol L⁻¹), organic matter OM (%) and Loripes density L (ind. m⁻²). (A) Model simulations at default setting without mutualistic interaction displayed damped oscillation (unstable) behaviour due to a negative feedback as a result of organic matter accumulation and sulfide toxicity. (B) When adding the mutualistic interaction, any produced sulfide is removed and oscillations disappear. (C) An increase (from m_n = 0.007 to m_n = 0.023) of seagrass background mortality causes slow-fast cycles in which the mutualism temporarily buffer against sulfide toxicity, but is not able to remove all sulfide produced, eventually causing seagrass collapse. Recovery occurs when organic matter and sulfide have disappeared from the system.