THis is one issue that should be worked on by the seasteading project because certainly there are marine species that maybe dislodged but if the project has enough study then maybe this can be taken care of. The idea that the project can have its own laws and be not under any country can be not an absolute not unless they can locate themselves in the middle of the Pacific Ocean which is actually not a viable one...in many cases the area is under a certain country's economic zone but what they do is to have a certain agreement with the country it is in as a sort of an experimentation and maybe the country is looking at the project as a possible tourist attraction which can mean a lot for the country's coffers later on so it can be a win-win situation. Anyway, the idea can be attractive and with the right technology can be a very viable one otherwise this can be just another failed human-made ideas.