We keep getting spammers. I have seen in this section that new members can subscribe and do not need authorisation.
Adding Authorisation increases the work load for moderates and is not fool proof, unless you require them to send some sort of hobby CV or so which will increase the work load even more.
An in-between solution could be to allow new members to subscribe automatically but block them from posting for the first N days. That will increase the work load for THEM and deny them a shoot and forget type of spam.
I am not sure how much flexibility this platform offers but spammers generally like to post in the the Tube section because that is the most active one. If possible you could make it even less attractive for them to force them to make their first post in the "introduce your self" section and and make them wait an other day before they can start posting in general. Also to be fair to regular users and discourage spammers beforehand, this should be explained in the sign on section.