Physical and Ecological Responses of Sandy Beaches to the 1997-98 El Nino

El Nino events elevate water levels, change wave direction and storm frequency, and provide an analogy to the likely impacts of climate change. Elevated sea levels intensify coastal erosion impacts affecting not only oceanfront property and recreational users, but also habitats and species that depend on the coast. This study examines physical and ecological responses to and recovery from the extreme 1997-98 El Nino along beaches of Isla Vista, California, a stretch of coastline dominated by unidirectional alongshore sediment transport. Using topographic light detection and ranging (LIDAR), physical measurements, and biological surveys we quantify physical changes and assess ecological responses. We quantify short-term reductions in beach widths (>60%) and sand volumes (similar to 80%). Although dune-backed beaches lost greater sand volumes, bluff-backed shorelines lost greater percentages of beach width. Four erosion hot spots were identified consistent with a pattern of beach reorientations. Macrophyte wrack abundance, a primary food for sandy beach ecosystems, was significantly correlated with dry sand beach width. Macroinvertebrate biomass was reduced and a decline in mean size of individuals persisted for several species. Abundance and species richness of shorebirds were lower during the El Nino. Beach segments and reorientations recovered at different times, on the basis of littoral drift direction, shoreline orientation, and wave exposure. The reorientation at the updrift beach impounded sand for >3 years after the El Nino, catalysing an erosion wave that propagated downdrift affecting downcoast beaches. Recovery of the updrift beach led to the widest beach widths shown in the historic record, whereas the downdrift beach underwent continued erosion >6 years after the El Nino. Recovery of wrack abundance and shorebirds to pre-El Nino levels took >3 years. Reductions in biomass and mean size of invertebrates were detected 2 years after the event. Recovery time lines provide information for coastal managers evaluating impacts and timing of erosion mitigation alternatives.