The fallout from a series of defaults at a New York hedge fund reverberated through markets for a second day on Monday, as global banks tried to size up their exposure to one firm’s string of bad bets. Shares in Credit Suisse, the Swiss bank, dropped 14 percent on Monday and the Japanese bank Nomura closed 16 percent lower, after the banks said they could face significant losses because of defaults by an American investment firm. U.S. stock futures fell on Monday, with the S&P 500 set to open 0.7 percent weaker.