The clean technologies sector fared the worst of all, with dollar investment plummeting 84 percent to $154 million.

It was the lowest level of venture investment in clean tech since 2005, according to the study, a fact that may seem unusual in light of the strong support the sector is receiving from the administration of U.S. President Barack Obama.

The drop is likely due to the "astronomical" amount of green-tech investments during the past couple of years, said Noubar Afeyan , managing partner and CEO of Flagship Ventures, during the conference call. "A lot of that money came in expecting a short-term pop ... which didn't happen. Having said that, I don't see it completely leaving. The most likely early beneficiary of a turnaround in the economy will be this sector."