These form the natural separation between lagoon and sea. Unlike the salt marshes, which are muddy or silty, the barrier islands are sandy and made up of dunes variously anchored by psammophile (sand-loving) vegetation typical of sandy coasts. Behind the sand bars in the direction of the lagoon, the sandbanks often extend some distance. The psammophilic plants have a number of adaptations including: long roots to reach water in depth that is in short supply at the surface, resistance to the salty environment, buds at different heights to avoid complete burial by windblown sand, accumulation of water in the leaves that they often look fleshy (succulent). They have also low transpiration to prevent excessive evaporation caused by strong sunlight. Man has flanked or replaced the barrier islands with embankments that recall the murazzi or “sea walls” of the Venetian lagoon. In the lagoons of Friuli Venezia Giulia, however, there are still long stretches of natural sandy coastline on the banks of the Orio and on the islands of S. Andrea and Martignano. Like with the salt marshes, river mouths and lagoons in general, the barrier islands are constantly changing, determined by the amount of sediment deposited or removed from the various sites. Due to many factors, the lagoon areas are currently subject to a prevailing erosive process with a reduction of areas emerging above water level, although there are some sites that run counter to this trend.