Seagrasses provide multiple ecosystem services and act as intense carbon sinks in coastal regions around the globe but are threatened by multiple anthropogenic pressures, leading to enhanced seagrass mortality that reflects in the spatial self-organization of the meadows. Spontaneous spatial vegetation patterns appear in such different ecosystems as drylands, peatlands, salt marshes, or seagrass meadows, and the mechanisms behind this phenomenon are still an open question in many cases. Here, we report on the formation of vegetation traveling pulses creating complex spatiotemporal patterns and rings in Mediterranean seagrass meadows. We show that these structures emerge due to an excitable behavior resulting from the coupled dynamics of vegetation and porewater hydrogen sulfide, toxic to seagrass, in the sediment. The resulting spatiotemporal patterns resemble those formed in other physical, chemical, and biological excitable media, but on a much larger scale. Based on theory, we derive a model that reproduces the observed seascapes and predicts the annihilation of these circular structures as they collide, a distinctive feature of excitable pulses. We show also that the patterns in field images and the empirically resolved radial profiles of vegetation density and sediment sulfide concentration across the structures are consistent with predictions from the theoretical model, which shows these structures to have diagnostic value, acting as a harbinger of the terminal state of the seagrass meadows prior to their collapse.
Bibliographical noteKAUST Repository Item: Exported on 2023-01-13
Acknowledgements: D.G., T.S., and E.H.-G.acknowledge financialsupportthroughgrantsMDM-2017-0711,RTI2018-095441-B-C22,andPID2021-123723OB-C22andE.M.,I.E.H.,andN.M.throughgrants RTI2018-095441-B-C21 and PID2021-123723OB-C21 funded by MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe. T.S.and D.G. acknowledge grant PRD2018/18-2 funded by LIET from the D. Gral.d’Innovació i Recerca (CAIB). D.R.-R. is supported by the Ministry of Universitiesthrough the ”Pla de Recuperació, Transformació i Resilència” and by the EU(NextGenerationEU), together with the Universitat de les Illes Balears. E.M. wassupported by a PhD contract (PRE2019-089301) of the Spanish Ministry ofScience and Innovation. C.M.D. was supported by King Abdullah University ofScience and Technology (KAUST) through the baseline funding.
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