Trades of 8.91 million, down 16 percent from a year earlier, were at their lowest level since 2006 at 8.91 million, the Municipal Securities Rulemaking Board reported Wednesday.

The face value of bonds in the transactions were the smallest in over a decade with $2.77 trillion. The number represented an 11 percent decrease from 2013.

From the syllabus of Wall Street 101, trouble begets volatility, and half of the top eight traded muni bonds in 2014 were Puerto Rico issues.

The municipal bond market is a sea of small issues.