Renewal after catastrophe
Extreme events such as the eruption of Mount St. Helens and the severe fires in Yellowstone National Park initially seemed to have left behind wastelands. Yet ecologists and other researchers discovered that in both cases, plants and other life rebounded much more quickly than anticipated. Now a new study of sandy beaches finds surprising resilience following the 8.8 magnitude earthquake and tsunami that rocked coastal Chile in February of 2010.
The Maule earthquake was the 6th largest event recorded by modern seismology and unleashed a tsunami, killing nearly 500 people. Communities in coastal areas around the world have been erecting seawalls for centuries in an effort to stem beach erosion and protect themselves against storms and tsunamis. Researchers from Southern University of Chile and the University of California, Santa Barbara had been researching the effects of such structures on plant and animal life on nine coastal beaches in Chile just prior to the earthquake. After it struck, they resurveyed the now dramatically altered areas.
As they had predicted, their pre-earthquake surveys found that species that live in the upper and mid-intertidal areas of sandy beaches are more affected by seawalls than those living in the lower shore areas. The upper intertidal zone is mostly terrestrial except during high tides and the mid intertidal zone is regularly exposed and submerged by tides. The low intertidal areas are only exposed during very low tides. Seawalls physically cover up part of the beach and cause sand in front of the walls to be lost until the beach eventually “drowns.”
The earthquake and tsunami brought about tremendous physical changes, drowning some beaches while creating sandy beach habitat in other areas. According to a press release by the National Science Foundation, which helped fund the study, the research team found that intertidal species were destroyed in the drowned beaches while newly widened beaches saw the return of life that had previously “vanished due to the effects of coastal armouring.”
From previous studies in California and Chile, said lead author Eduardo Jaramillo of the Universidad Austral de Chile, “…we knew that building coastal defense structures, such as seawalls, decreases beach area, and that a seawall results in the decline of intertidal diversity. But after the earthquake, where significant continental uplift occurred, the beach area that had been lost due to coastal armoring has now been restored,” said Jaramillo. “And the re-colonization of the mobile fauna [such as crabs] was underway just weeks afterward.”
Jaramillo E, Dugan JE, Hubbard DM, Melnick D, Manzano M, Duarte C, Campos C, & Sanchez R (2012). Ecological Implications of Extreme Events: Footprints of the 2010 Earthquake along the Chilean Coast. PloS one, 7 (5) PMID: 22567101
Photos: Researchers use sieves to find intertidal animals. Credit: Eduardo Jaramillo; Seawall at Arroyo Quemado, CA. Credit: David Hubbard.