(CNNMoney) — Google’s recent change to its search algorithm has dramatically shaken up the businesses of websites that moved up or down its search rankings. Sites whose rankings rose to the top found that their traffic and revenue soared — but the adjustment had an equally devastating effect on those that were dropped.  The Online Publishers Association, a group of content producers comprising many of the Internet’s largest properties (including CNN.com), estimates that the algorithm change shifted $1 billion in annual revenue.

Some of the losers felt the hit immediately. Mahalo.com laid off 10% of its workforce last week thanks to what CEO Jason Calacanis called “a significant dip in our traffic and revenue.”  The stakes are high in the Google-placement game. The top spot on a search page typically attracts 20% to 30% of the page’s clicks, according to Adam Bunn, SEO director of Greenlight. After that comes an enormous tail-off: Positions 2 to 3 generate 5% to 10% of the clicks, and links below the fold receive less than 1% of users’ attention. Fall off to the second page and your search-engine-driven clicks will be negligible.  With control of two-thirds of the U.S. search market, Google (GOOG,Fortune 500) steers a tremendous amount of traffic to websites. Many of them rely exclusively on advertising dollars to make money.That means that positioning in Google’s search results can be a life-or-death issue for a business.

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