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Global Climate Change May Spread Snails Into Coastal Salt Marshes

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    Fw: [WildlifeConservationDepartment] ... for the WCD 16 December 2005 Snails mount attack on US wetlands Coastal salt marshes might be overrun by snails if
    Message 1 of 1 , Dec 16, 2005
      Fw: [WildlifeConservationDepartment]
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      for the WCD

      16 December 2005

      Snails mount attack on US wetlands
      Coastal salt marshes might be overrun by snails if droughts
      worsen with climate change.
      by Charlotte Schubert
      Nature

      Swarms of fungus-eating snails have laid waste to miles of US coastal
      wetlands that are already reeling from drought, say researchers in
      the southern United States. And global warming, they say, might
      exacerbate ecological breakdowns that give these plant-munching
      beasts the upper hand.

      The marsh periwinkle (Littoraria irrorata) could be considered
      charming by some standards. It is about 2.5 centimetres long and has
      a clever feeding trick: it rakes the surface of marsh grass, creating
      a home for tasty and nutritional fungi. But when the snails get
      together, it can get ugly.

      The snails graze on marsh cordgrass (Spartina alterniflora), which
      grows in vast fields in coastal areas down the eastern seaboard and
      into Louisiana. Usually the grass and snails live in harmony. But
      from 1999 to 2001, the region suffered from a drought. This made the
      grass more susceptible to fungal infection and snail infestation,
      says Brian Silliman, lead researcher of the study at the University
      of Florida in Gainesville.

      Climate models predict that droughts will last longer in a warming
      world, putting more stress on coastal ecosystems.

      Overkill

      In one part of a Louisiana wetland, Silliman counted 2,000 snails per
      square metre. "There were layers and layers of snails pressing down
      on the grass. Normally the grass is four feet tall, but it had been
      compressed to just one foot," he says. "There were snails on every
      inch of it." When the grass has been worn away, the snails take off
      at the unsnail-like pace of 15 metres per hour to find new gardening
      grounds.

      More than 250,000 acres of southern coastline has died off in the
      past six years. In places such as Louisiana, other factors related to
      human development clearly come into play. But the snails have
      certainly contributed to large patches of barren mud in many of the
      wetlands, says Silliman.

      To show this, he and his colleagues created snail-free zones in
      marshes by caging out the creatures. Spartina flourished in these
      zones but died outside of them. The researchers also mimicked the
      effects of drought by increasing the salinity of patches of marsh. In
      these areas, the grass became sickly and the snails thrived. The
      findings appear in the current issue of Science1.

      Snail explosion

      The idea that weakened wetlands can make way for explosions in
      herbivore populations is not new, says Bill Mitsch, a wetlands expert
      at Ohio State University in Columbus. But Silliman and his colleagues
      have gone a step further by proposing that the snails can cause so
      much havoc. Mitsch is not entirely convinced of the heavy impact of
      the snails, but notes that the work disturbingly suggests that other
      coastal areas, such as mangrove forests, might be similarly
      vulnerable.

      Silliman is now looking at a coastal environment in Argentina that is
      dominated by another herbivore, plant-eating crabs, to see whether
      they too take over vegetation weakened by drought.

      Since 2001, the US wetlands have begun to recover from the drought,
      and the grass is growing back, although many areas were again
      devastated by flooding after Hurricane Katrina.

      References

      1.Silliman B. R., et al. Science, 310. 1803 - 1806 (2005).

      �2005 Nature Publishing Group

      NOTICE: In accordance with Title 17 U.S.C. Section 107, this
      material is distributed to the WCD membership without profit, for
      research and educational purposes only.

      for the WCD








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