I tried again, and this time I get "Posts that look like spam are blocked", and a similar message if I try to leave a link in a comment.

I wonder if spammers have been vandalizing Wikispecies and posting the links, but unlike Wikipedia the editors of Wikispecies struggle to remove the spam in time? The project has hundreds of thousands of pages, but the vast majority would have very little content or oversight. It could be the Wiki project with the worst pages-per-editor ratio.

There isn't pornography, or at least only indirectly — Wikispecies doesn't host any images itself (says https://en.wikipedia.org/wiki/Wikispecies ).