Users and moderators of Reddit's newest default subforums have reacted in varying ways – from fighting back to opting out – after being thrust into the limelight as part of the site's recent redesign.

The front page of the news and networking site's biggest community for women, r/TwoXChromosomes, was dominated for much of Friday and Saturday with fairly graphic posts about menstruation and toilet habits. This was the result of a protest by regular members who felt undermined by an influx of new – and not always entirely genuine – contributors.

Meanwhile, moderators of r/dataisbeautiful, a subreddit devoted to data visualisation, tightened up the rules submitters have to follow, requiring original creations to provide the data source, and banning contributions from members who are not explicitly subscribed to the subreddit.

The music forum r/listentothis, with the help of a large collection of automated moderation tools, has managed to keep its rules rigidly enforced. Bands with more than 500,000 listeners on last.fm and songs with more than a million views are automatically removed, as is anything that's not a song. But the submission rate on the forum has doubled and there has been a spike in spam, which the robots can't handle.

Each is reacting to the influx of new members of the community brought by inclusion of their subreddits on the site's default list, to which all new members are automatically subscribed and which is shown to users who aren't logged in.

TwoXChromosomes, for example, had 180,000 members subscribed as of last week, but over a course of an average month the reddit front page receives 100 million unique users.

At their worst, those new members flood the subreddits with submissions out of character for the forums, which have often spent years building up codes of conduct and their own community norms. "There has never been a default sub that didn't suffer in quality, and there never will be," says user LinuxLinus on the DataIsBeautiful subreddit. "It's a numbers game: we can report and downvote as much as we like, but unless you have 50 mods, the shitposting will overwhelm everything else, just as it has on every default sub."

KaylaS, a user of TwoXChromosomes, agrees. "There were a few trolls and ignorant people on here before but most people on here were serious subscribers and there were enough of us to counteract them with downvotes and report. Not anymore. We can all say goodbye to a safe place on reddit for women. I know I won't feel comfortable here anymore."

While most users only found out that their favourite subreddits were becoming default subs when Reddit announced it publicly on Wednesday, the moderators of each sub were given advance warning – and the opportunity to decline. Some redditors, such as KaylaS, wish they'd taken that chance, but others have placed their trust in the moderators.

"I know that a lot of people are afraid of the defaulting of the sub," writes KennysConstitutional on r/listentothis "but… we have very dedicated moderators who are resourceful and determined to keep this place from going to shit."

But moderators can only do so much, particularly against an influx of users who are not so much clueless as actively hostile. That was the problem faced by TwoXChromosomes, which has to deal with being the most prominent space for women on a site known more for being the home of numerous communities of "men's rights" activists and "pick-up artists".

Some members of those communities begrudged having a subreddit just for women included in the defaults, seeing it as an example of discrimination against men. Just hours after the change was instituted, users reported abuse in the private message system of Reddit, something no moderator can prevent.

But rather than being cowed, many users of TwoXChromosomes are fighting back; hence the rush of "TMI" posts. "For those of you not wanting to see girl-talk on your frontpage because we are "gross", you can unsubscribe," says the author of "Oh the period shits…" a front page post with 1144 comments and 1672 net upvotes.

"Serious question: is this how it normally is around here?" asked one new user in response.

"I've never known TwoX to shy away from the more gnarly TMI [too much information] topics that women talk about, so in a way, yes," confirmed another. "But I think we might be pulling out all the stops in retaliation."

• Reddit shakes up the defaults again: which are the best of the new intake?