With 25 firms within the city limits, New Haven is at the center of Connecticut’s substantial biotechnology sector. But biotech companies have not been immune to the slumping economy, finding it difficult to continue the expansion of the past decade.

The biotech sector is responsible for 16,500 jobs in Connecticut, many of which are lucrative positions in research and development, said Gary Wilson, a representative of Connecticut United for Research Excellence, an industry trade group. In addition, the sector supports over 57,000 jobs in other fields, with an estimated $6.4 billion impact on the Connecticut economy.

But the latest economic downturn has hurt many of Connecticut’s biotech firms, Wilson said.

“A number of companies have had appropriate downsizing,” he said. “But we hope to see the appropriate management moves when the venture capital becomes available again.”

Connecticut currently receives 12 percent of all dollars spent nationwide on pharmaceutical research. The mean salary for positions in research and development is $63,000, with about a third of researchers holding doctorates, Wilson said.

“The state has been vigorous in assisting the development of these companies,” said Michael Morand, Yale’s associate vice president for New Haven and state affairs.

The state recently passed a research tax credit that reimburses 65 percent of the cost of research in bioscience companies, Wilson said. The estimated cost of developing a successful pharmaceutical has been estimated by industry experts to be as high as $800 million.

“New Haven is an enterprise zone,” Wilson said. He added that New Haven has tried to draw in companies with numerous incentives — including other tax credits, abatements and loan guarantees — and that New Haven is home to many “quality companies.”

Morand said research from Yale has also spurred several biotech companies.

“President [Richard] Levin has worked hard to take research from the lab to the market,” he said.

CuraGen Corp., one of New Haven’s larger biotech firms, started in 1993 in the basement of a Yale alumnus, Jonathan Rothberg GRD ’91.

Rothberg now serves as chief executive officer of a company that employs roughly 500 people and has over $450 million targeted toward research, said Shannon Slapierre, a CuraGen spokeswoman.

“CuraGen has recruited a number of people from Yale — including a number of spouses of Yale students,” Slapierre said.

CuraGen, which focuses on the intersection of information technology and molecular biology, has not been severely affected by the economic downturn.

“We’re fortunate that we’re able to raise enough money to sustain research,” Slapierre said. The company has three to five years of financial resources at this point, she added.

Although Curagen has not laid off any employees, Slapierre did say management is taking a “conservative approach” in expanding the company right now.

“It’s been a challenge,” she said.