Trading on U.S. equity markets averaged 6.6 billion shares a day in March, according to Tabb Group. That was down from 6.9 billion in February.

As such, March was “a quiet month,” with market volatility fairly light, according to Tabb research analyst Cheyenne Morgan.

The main measure of market nervousness, the CBOE S&P 500 Volatility Index dropping below 15 during the month, she noted.

At the height of the credit crisis three years ago, the VIX climbed to 80. Last year, when Standard & Poor’s downgraded U.S. debt for the first time, the index hit 40.

The absence of volatility tends to mean less trading. “Volatility is highly correlated with equity volumes as traders find more opportunities for profits, so when prices reverberate back and forth, they tend to be more active,’’ Tabb noted.

Concerns about different European countries’ ability to pay their debts remained. But, “there was no earth-shattering news last month to light a fire under trading,’’ the research firm said.

NYSE Euronext, for instance, reported that its volume of trading in domestic stocks was down 24 percent in March 2012, compared to a year ago. And, as Securities Technology Monitor reported last week, trading volume is roughly on a par now with 2007.

Overall, volume in the first quarter of 2012 was down 19 percent from 2011, Tabb said.

Tabb quotes one unidentified trader as saying, “Every week, volumes get worse and worse and worse and it’s crushing me.”

“High-frequency traders are also suffering since low volatility makes it very difficult for highly quantitative, very short-term alpha traders to make any profits,’’ Tabb said.

Equity funds had an estimated $4.43 billion in net redemptions in the week ended March 28, Tabb noted. That is the most since $8.77 billion in redemptions in the week ended January 4, according to the Investment Company Institute, the U.S. mutual fund trade organization.

“Unless we were forced to experience another market-shocking event like the U.S. credit downgrade or 2011 flash crash – both of which we could all do without – volumes will most likely remain low through the fall,’’ Tabb said.