Caulerpa, like most seaweeds, can reproduce by producing eggs and sperm cells which fertilise in the water, and then, obviously, spread for kilometers by tidal currents. Although fragmentation also can spread it, once it is established, the action of a few fragments from anchoring ain't going to make much difference.
Once again, like the over reaction to kauri dieback, decisions made without scientific evidence. We pay all the time for the foreign species brought in by international travelling ships. Does anyone really think that ships are carefully and fully compliant about emptying thei