The online giant’s move to slash prices on everything from organic baby kale to fair-trade bananas on the same day its $13.7 billion acquisition of Whole Foods Market Inc. closes showed the “High-velocity decision making” Amazon founder Jeff Bezos claims as his hallmark, and sent shares of Kroger Co., Costco Wholesale Corp. and Wal-Mart Stores Inc. reeling Thursday.

While this won’t exactly bring responsibly farmed salmon to the masses – after all, Whole Foods stores will remain in high-rent neighborhoods – the price reductions could draw in curious new shoppers and present brick-and-mortar retailers with a dilemma.

For years, organic food was a niche category, but Whole Foods showed t was growing demand as it opened more than 400 stores across the country.

As organics became more widespread, the traditional supermarkets undercut Whole Foods on price, and the chain’s same-store sales have fallen for eight straight quarters as it struggled to respond.

Amazon will speed those efforts by layering on discounts for Prime members, who are typically shopping at Whole Foods already.

Nearly two-thirds of Whole Foods’ regular customers are Prime members, according to retail consultancy Magid.

“That’s a good thing but with this deal, Amazon bought the same customers it already had. So they have to expand beyond current Whole Foods customers by offering more value.” Whether Amazon can convert those value-seekers into long-term customers will be the challenge, Barthashus said.

Even with all this attention, Whole Foods is still a small player in the U.S. grocery market compared with Wal-Mart and Kroger, who together garner more than 30 percent of sales.