1st invaded the southeastern U.S. in the 1930's, probably in soil used as ballast in cargo ships. They are more aggressive than the black imported fire ants, which have been displaced by the red ants. Ice plant is native to South Africa but came to the U.S. in the 1800's. This ecosystem is already threatened due to loss of habitat. The ice plant makes matters worse by outcompeting native plants.
Ice plant is very strong, often stronger than the native plants themselves.
Also, once ice plant dies it leaves behind so much salt that other native plants don't want to live there. All of this lessens the diversity of wetland plants. This means that endangered species like the Clapper Rail lose their homes. Native to the Carribean, a strain of this saltwater aquarium plant has devastated the Mediterrean. Unfortunately it was discovered right here in San Diego, probably after someone dumped the contents of their aquarium in the lagoon.