CHICAGO – As Mazda Motor Corp. celebrates the 20th anniversary of the venerable MX-5 Miata sports car, the bottom has fallen out in the 2-seat roadster segment due to the ailing economy.

In 2008, the Middle Specialty car segment in which the Miata resides was off 27.2% vs. like-2007 to 191,213 units, while Mazda as a whole saw sales decline 10.9% to 263,949, Ward’s data shows. Miata sales for full-year 2008 were down 27.2% to 10,977 units, mirroring the segment decline.

A car such as the Miata is particularly vulnerable to economic downturns, as roadsters largely are bought as recreational vehicles and seldom used as daily drivers, Mazda North American Operations CEO and President Jim O’Sullivan says.

“The Miata, in some cases, was a bit of an indulgent-type vehicle, like the extra car for the garage,” O’Sullivan tells Ward’s at the recent auto show here. “We think when the economy comes back the segment will come back with it.”

To commemorate the Miata’s 20th anniversary, Mazda held a small celebration at the show, where the sports car made its debut in 1989.

Since then, Mazda has sold 857,201 Miatas globally, earning it a place in the Guinness Book of World Records as the highest-volume 2-seat sports car in history.

“The British roadsters were the ones that really defined the segment,” O’Sullivan says of iconic sports cars such as the Triumph Spitfire and MGB. “And when they exited (the segment), we came in because it provided an opportunity for us.”

For the ‘09 model year, the Miata has undegone a significant refreshening, receiving new front and rear fascias, a redesigned interior and a modest 3-4 hp bump in power output. The ‘09 model currently is hitting dealerships.

The Miata is now in its third generation, having been fully redesigned in 1998 and 2005.

Although sports-car sales are down, the Miata remains the No.1 seller in its segment and will benefit from the recent departure of the Honda S2000, O’Sullivan says.

Honda Motor Co. Ltd. last month announced it was pulling the plug on its S2000 roadster, saying the ‘09 model year will mark the 2-seater’s last year in production.

The S2000, which debuted in 1999 as an ‘00 model, currently is sold in 64 countries. Cumulative sales total more than 110,000 units worldwide, Honda says, with more than 65,000 sold in the U.S. since it bowed.

Last year, 2,538 S2000s were delivered in the U.S., down 41.0% from 2007 levels, according to Ward’s data.

“When there are fewer competitors, there are obviously more opportunities,” O’Sullivan says. “So with Honda vacating the segment, it could be an opportunity for us.”

Regardless of economic conditions, O’Sullivan says Mazda has no plans to drop the Miata from its lineup, noting the car is “very much a part of our cycle plan moving forward.”

Adds Sullivan: “We feel the Miata prepared Mazda for where we are in design, great driving dynamics and value. It helped make us a very relative brand for this economy and this environment.”