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 a ecting 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