Net occupied space in Greater Boston shrank by 4.4 million square feet during 2009 and the vacancy rate increased from 15.5 percent to 18.4 percent, according to a new report by Colliers Meredith & Grew.

The fourth quarter 2009 market snapshot details occupancy and absorption statistics for the Boston, Cambridge and suburban Boston office/R&D markets. It found the fourth quarter represented the sixth consecutive quarter of contraction, with 540,000 square feet of negative absorption.

Although the pace of the market’s deterioration slowed over the latter half of 2009, nearly 5 million square feet has been vacated since the recession began in December 2007, according to Colliers Meredith & Grew.

Many of the tenants who signed leases in 2009 chose to renew at their existing locations, rather than relocate. Weighted average asking rents varied depending on market segment, but on average were approximately 20 percent lower than they were a year ago, the report found.

This year, deterioration in rental rates is expected to be more modest. Although the market appears to be bottoming out, conditions will remain challenging at least through the first half of 2010 or until the labor and financial markets stabilize, according to the report.