Morphodynamic study of a 2018 mass-stranding event at Punta Umbria Beach (Spain): effect of Atlantic Storm Emma on benthic marine organisms

Very few mass stranding events of invertebrates have been reported. In this paper, we report a mass stranding of multiple benthic organisms occurred at Punta Umbría beach (S Spain) after the passage of storm Emma (28 February to 5 March 2018). The most abundant organisms were identified, and exceptional meteorological and oceanographic events were analyzed, as a basis to understand the causes of stranding. The morphodynamic changes affecting the beach profile during the storm were inferred using a cross shore depth-integrated and time averaged numerical model (CSHORE). Among the stranded species, decapods (Upogebia spp., Atelecyclus undecimdentatus), sipunculids (Sipunculus nudus), starfish (Astropecten sp.), and sessile tunicates were dominant. Storm Emma involved extreme significant wave heights of up to 7.27 m, low pressures, strong SW winds, precipitations and spring tides that modified the seabed elevation to depth as deep as −10 m. Simulations suggest that benthic organisms living at a water depth between −10 to −0.3 m were buried under a layer of sediment of up to ca. 10 cm deposited during the storm. This burial preceded the transport of intertidal and subtidal benthic organisms to the dry beach, causing their stranding. Impacts on the quality of habitat, biodiversity and the productivity of coastal ecosystems are discussed.