Facebook surpassed Google as the top source of referral traffic online publishers in July, it was reported by Parse.ly’s network of nearly 400 digital publishers. Facebook’s share of referral traffic reached 38.3 percent, compared to Google’s 35.8 percent.

The website traffic may not cover the entire Internet, but the Pars.ly list of 400 media outlets includes major publishers, such as Wired, The Atlantic, Reuters and The Daily Telegraph, as well as high-profile digital-only publishers like Mashable, The Next Web and Business Insider. All together, the publishers have 6 billion pages views and over a billion unique visitors a month.

Facebook Instant Articles

Facebook’s effort to form partnerships with publishers to curate and promote content is a major reason behind the shift, Parse.ly Chief Technology Officer Andrew Montalenti told Social Times. With Instant Articles, Facebook users view articles from publishers in their news feeds, as opposed to accessing them by linking to the publishers’ websites. Facebook realized that many online conversations were happening around major news, media and information, but the user-generated content was not enough to sustain the interest of Facebook’s users, he said. Facebook is courting media companies to encourage them to care about Facebook content optimization as much as they care about search optimization.

Predicting an overall trend with certainty is difficult. Referral traffic fluctuates. Referral traffic from Facebook was slightly higher than Google’s in October 2014, but then jumped significantly in July.

Montalenti predicts Facebook will continue developing publisher relationships and prioritize content in the News Feed. However, its portion of referral traffic may have plateaued. The Parse.ly data reveals a trend in the media industry, but not necessarily the overall web. Facebook and Google will probably remain roughly equal as referral giants.

The Growth of Social Media

The revelation underscores how social media in general — and Facebook in particular — has grown as a major traffic referral source. Shareaholic, a content marketing hub, had previously reported that social media has become the largest driver of website referral traffic. Social media generated over 31% of all referral traffic at the end of 2014, up from 22.71% the previous year.

“There’s a lot of effort among media companies being placed on specific social channels like Twitter, but our data shows that Twitter is basically a distant traffic source,” Montalenti told Fortune. “That’s unfortunate because Facebook is a lot less transparent around things like how the algorithm functions. There’s a lot more useful data from Twitter about their content, but FB is more like a black box in terms of how it operates. And yet it’s this huge and growing traffic source.”

The Facebook Impact on PR

The rise of Facebook as a top traffic referral source for major publishers has implications for PR. It may change how content is packaged and consumed and how PR creates content and works with publishers. Clearly, effective PR placement will now require placement in Facebook news feeds. How to do that isn’t yet clear, since the Facebook algorithm for creating news feeds is still a mystery.

PR professionals’ relationships with journals may change. Publishers may rearrange job functions of staff members or perhaps hire new writers with knowledge of writing for Facebook readers.

PR pros with multimedia skills will gain a greater advantage. Although publishers could simply upload their long-form articles, the social media network places greater emphasis on photos, maps and especially videos.

The Instant Articles may also change tracking of media coverage. It’s not clear how PR will track and measure coverage and compare coverage of different media outlets. For example, should an article viewed on Facebook be rated differently for purposes of PR measurement than when it is viewed on the news organization’s own website? Is there a difference in the value of readers who search out and read/view an article on a website as opposed to a reader where the article is automatically placed in front of the reader?

If PR cannot obtain Facebook data, PR measurement would miss a major segment of readership when measuring the impact of news releases and other news mentions.

Bottom Line: Facebook overtook Google as a traffic referrer for major Internet publishers, a fact that has major ramifications for the media industry and public relations. News outlets may focus of optimization for Facebook as much as search engine optimizations, and PR could gradually change how it creates content and works with publishers.