Localised Effects of a Mega-Disturbance: Spatiotemporal Responses of Intertidal Sandy Shore Communities to the 2010 Chilean Earthquake

Abstract

Determining the effects of unpredictable disturbances on dynamic ecological systems is challenged by the paucity of appropriate temporal and spatial coverage of data. On 27 February 2010, an 8.8 Mw mega-earthquake and tsunami struck central Chile and caused coastal land-level changes, massive damage to coastal infrastructure, and widespread mortality of coastal organisms. Wave-exposed sandy beaches showed significant changes of species abundances from before to after the earthquake, but the highly dynamic biotic and abiotic conditions of these habitats make difficult to draw clear-cut conclusions from these patterns. Here, we analysed a beyond-BACI (Before-After Control-Impact) sampling design to test whether the effects of the Maule earthquake on sandy-shore species diversity, abundance, and structure were heterogeneous along the shore. Invertebrate species abundances were quantified before (i.e. February 2010) and after (i.e. March 2010, September 2010, and March 2011) the earthquake at three sandy shores randomly located within the earthquake rupture area and three sites within a "control" area located >400 km southward from epicentre. Immediately after the earthquake took place, the three sites located in the rupture area showed anomalous beach-profile uplifts that did not comply with the erosion (i.e. "negative" uplifts) that regularly occurs during late summer in the region. Species richness, abundance, and community structure significantly varied from before to after the strike, but these patterns of change varied among sites within both areas. Only the site with the strongest and persistent beach-profile uplift within the rupture area showed significant concomitant changes in species richness and community structure; after 13 months, this community showed a similar multivariate structure to the before-disturbance state. This site, in particular, was located in the section of the rupture area that received most of the impact of the after-earthquake tsunami. Therefore, our results suggest that the effects of the Maule mega-earthquake on the ecological communities were spatially heterogeneous and highly localised. We suggest that high mobility and other species' adaptations to the dynamic environmental conditions of sandy beaches might explain the comparatively high resilience of these assemblages. With this work we hope to motivate further experimental research on the role of individual- and population-level properties in the response of sandy-beach communities to interacting sources of disturbances.

Fig 1. Map of the sampling sites in the central Chilean coast.

The Maule earthquake epicentre is indicated by a red star. Cocholgüe, Hualpén, and Llico were located within the earthquake rupture area (red area) and <150 km of lineal distance to epicentre (∼36°S). Mehuín, La Misión, and Maicolpué were located within the “control” area (blue area) and >400 km away from the epicentre (∼40°S).

Fig 2. Profile of beaches in the earthquake rupture and control areas.

For each site, each line represents the profile of the sampling beach at each sampling time. “Metres above MLW” (mean low water) denote the height of the beach at a given distance from the coastline. Profiles are given for before (February 2010, blue line) and after (March 2010, red; September 2010, green; and March 2011, black line) the earthquake and tsunami of February 27, 2010.

Fig 3. Coastal uplift and changes in species richness and total abundance from before (February 2010) to immediately after the earthquake (March 2010).

Mean change was calculated by randomly pairing replicate transects from before- and after-earthquake samples and then averaging these values for each site. Values are given as mean ± 1 S.E.

Fig 4. Number of invertebrate species in the intertidal sandy shores.

Values are given for before (February 2010) and after (March 2010, September 2010, and March 2011) the earthquake and tsunami of February 27, 2010. Error bars denote ± 1 S.E.

Fig 5. Total species abundance in the intertidal sandy shores.

Values are given for before (February 2010) and after (March 2010, September 2010, and March 2011) earthquake and tsunami of February 27, 2010. Error bars denote ±1 S.E. *Note difference y-axis scale for Cocholgüe.

Fig 6. Principal Coordinates Analysis (PCoA) of the spatiotemporal patterns of community structure of six intertidal sandy shores.

Ordination plot includes the rupture and control areas (empty and filled symbols, respectively) before (February 2010) and after (March 2010, September 2010, and March 2011) the earthquake and tsunami of February 27, 2010. Each symbol represent the centroid of five replicate transects deployed in each site and time.