When I was maintaining my own site using wordpress, I got lots of SPAM similar to what I see in here. Mostly gibberish, nonsense ramblings, lots of text and tons of links to who knows where.
The key is to obviously ignore them and never by any means click on any of the links or respond to them directly, that will just make it worse.
I used askimet on my old wordpress site and it helped tremendously, it works similar to that of email filtering and rules. The main thing is selecting certain keywords or ip addresses as the filtering process, and maybe adding in the policy where only registered and/or approved users can create posts. Since I am not sure what technology this site is using to drive their forums, I’m not sure if askimet or something similar to it would work here.
It can be a daunting task to filter traffic, you never want to steer people away unless they are up to no good, but it is better to be proactive then reactive.