SAN FRANCISCO — Alex Andon, 24, a graduate of Duke University in biology, was laid off from a biotech company last May. For months he sought new work. Then, frustrated with the hunt, he turned to jellyfish.

In an apartment he shares here with six roommates, Mr. Andon started a business in September building jellyfish aquariums, capitalizing on new technology that helps the fragile creatures survive in captivity. He has sold three tanks, one for $25,000 to a restaurant, and is starting a Web site to sell desktop versions for $350.

“I keep getting stung,” he said. And his crowded home office is filled with beakers and test tubes of jellyfish food. “But it beats looking for work. I hate looking for work.”

Plenty of other laid-off workers across the country, burned out by a merciless job market, are building business plans instead of sending out résumés. For these people, recession has become the mother of invention.

Economists say that when the economy takes a dive, it is common for people to turn to their inner entrepreneur to try to make their own work. But they say that it takes months for that mentality to sink in, and that this is about the time in the economic cycle when it really starts to happen — when the formerly employed realize that traditional job searches are not working, and that they are running out of time and money.

Mark V. Cannice, executive director of the entrepreneurship program at the University of San Francisco, calls the phenomenon “forced entrepreneurship.”

“If there is a silver lining, the large-scale downsizing from major companies will release a lot of new entrepreneurial talent and ideas — scientists, engineers, business folks now looking to do other things,” Mr. Cannice said. “It’s a Darwinian unleashing of talent into the entrepreneurial ecosystem.”

Even in prosperous times, entrepreneurs have a daunting failure rate. But those who succeed could play a big role in turning the economy around because tiny companies are actually big employers. In 2008, 3.8 million companies had fewer than 10 workers, and they employed 12.4 million people, or roughly 11 percent of the private sector work force, according to the Bureau of Labor Statistics.

Economists say there are some peculiarities to this wave of downturn start-ups. Chiefly, the Internet has given people an extraordinary tool not just to market their ideas but also to find business partners and suppliers, and to do all kinds of functions on the cheap: keeping the books, interacting with customers, even turning a small idea into a big idea.

The goal for many entrepreneurs nowadays is not to create a company that will someday make billions but to come up with an idea that will produce revenue quickly, said Jerome S. Engel, director for the center for entrepreneurship at the Berkeley Haas School of Business. Mr. Engel said many people will focus on serving immediate needs for individuals and businesses.