Can storms and shore armouring exert additive effects on sandy-beach habitats and biota?

Increased storminess is a likely consequence of global climate change; its effects may be most dramatic on coasts dominated by sandy beaches. This scenario demands that the impacts of storms and the role of armouring structures, constructed as storm defences, are better understood. Here, we assess how a relatively small storm affected beach morphology and macrobenthos, and whether a seawall can modulate such impacts. The study system was a small (< 1.5 km long) beach, bisected into parts with and without a seawall. The beach became narrower and steeper during the storm, when 26% of the subaerial sediment prism eroded from the armoured section; sand losses on the unarmoured part were one-fifth of those on the armoured part. Densities of ghost crabs (Ocypode) dropped significantly (36%) and were to some extent modulated by shore armouring; losses were high (62%) just seawards of the seawall where post-storm densities remained consistently lower. There was no ecological recovery in the short term, with most (83%) post-storm density values of crabs being lower, and crab counts in front of the seawall being depressed up to 3 months after the storm. Seawalls can change the resilience of beaches to storms, which may result in stronger ecological effects on armoured coasts.