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Ponies, plants adapt to harsh barrier island - June 26, 2013

Barrier islands are dynamic ecosystems, always in motion. With the ocean on one side and a coastal bay, sound or lagoon on the other, a barrier island is hounded all hours of the day and night by waves and wind coming off the surrounding bodies of water. But despite these harsh conditions, life still thrives on the narrow strips of sand and mud. Plant and animal species adapt to survive the difficult conditions they constantly face on these exposed islands.

Starting in the ocean and walking toward the shore, one would first encounter the beach/dune habitat that eventually gives way to the maritime forest habitat. As one continues into the forest, it gives way to marshes that eventually lead into the coastal body of water. Due to the dynamic nature of these habitats, animals and plants that have colonized these areas have adapted morphologically and behaviorally to take better advantage of their surroundings.­

A perfect example of animals adapting to these environments are the world famous Assateague ponies. The ponies are regular horses that were put on the island roughly 250-300 years ago by local colonists looking to evade taxes on livestock. Throughout the years, the ponies changed to look like the animals we are now familiar with today on the Assateague side of the island; the Chincoteague ponies are not wild and do not fend for themselves, therefore they have not undergone such a dramatic physical change as their Maryland cousins.­

The Assateague ponies have adapted to life on the barrier island well. They are now shorter than their mainland cousins and look much more bloated. This physical change is due to their food source. The Assateague ponies eat a lot of plants covered with salt from the ocean spray and many salt marsh grasses, which can contain large quantities of salt, as well. In order to stay hydrated, the ponies must drink 3 to 4 times more fresh water than a regular horse would, which gives them the bloated look.

The ponies have also adapted behaviorally to life on the island. During hot, summer days, the ponies will generally stay on the beaches and dunes to escape the swarms of mosquitoes and biting flies than inhabit the inland portions of the island. During storms and bad weather days, the ponies will move inland toward the maritime forests and use the trees and shrubs as buffers against the harsh wind and rain that occurs on the island.

The ponies are not the only ­organisms that have adapted to the island; the black and loblolly pines have also adapted well to life on this unforgiving stretch of sand. The trees on Assateague never reach full height; they are shortened due to a lack of vital nutrients and salt spray from the ocean. These pine trees also do not grow to their full height to avoid toppling in high winds which can reach between 25-30 mph in the winter and even higher in big storms like Hurricane Sandy.

The endangered sea beach amaranth is also perfectly adapted to life on a barrier island. These small plants live mostly in overwash areas on the island — areas where large waves from storm action have pushed sand further inland away from the beach. These plants have hard, thick leaves which collect and store water.

These plants and animals are only a few examples of the amazing adaptation strategies that have evolved to deal with the harsh and ever-changing conditions of Assateague island and barrier islands like it. Throughout countless generations, these species of flora and fauna have become altered from their mainland cousins in order to have a better chance to survive and reproduce in these difficult, dynamic islands.­
 

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