And to come back to the topic of the original post: there's an invasive species of Japanese oysters in the Dutch Wadden Sea that you're free to harvest if you're in the neighbourhood. Although the debate on whether they are an ecological disaster or help restore the environment is not set, it's probably going to be the former if left unchecked, so you'll probably be helping out in the process.

https://nl.wikipedia.org/wiki/Japanse_oester