Effects of marine warming on the spatial distribution of Posidonia oceanica in the marine ecosystems

The dynamics of Posidonia oceanica density, an endemic Mediterranean seagrass species supporting high biodiversity levels, is analysed using the Advection-Branching-Death model, which considers both long-range competitive and short-range facilitative processes [1]. The model exhibits two homogeneous equilibrium states: a continuous seagrass meadow and a bare soil, which may coexist under specific parameter regimes. The performed analysis shows that the mortality rate of Posidonia oceanica, linked to environmental variables, such as seawater temperature (including accumulated degree-day anomalies), is a key parameter predicting critical situations leading to biomass loss [2]. The model is therefore used to investigate the effects of environmental stressors on the spatial distribution of P. oceanica meadows. The numerical analysis indicates that even mild increases in mortality rate can destabilize the populated homogeneous state via a Turing bifurcation [3], leading to the emergence of spatial patterns. These patterns correspond to patchy heterogeneous configurations, that enhance the plant’s ability to cope with moderate environmental stress, revealing an intrinsic self-organizing and adaptive response of the ecosystem. However, when environmental changes-such as global warming or other persistent harmful conditions-push mortality rates beyond the threshold for the existence of patterned states, the system may undergo a transition toward desertification. In this case, this shift becomes irreversible, as simply reducing the mortality rate is insufficient to restore the original ecosystem. Overall, the model allows for the prediction of how adverse environmental factors may affect the spatial distribution and resilience of Posidonia oceanica meadows in Mediterranean marine ecosystems.