A number of high-frequency firms closing down in the midst of a sharp market drop can "widen markets out substantially," said Jamie Selway, managing director of New York broker White Cap Trading.
High-frequency firms have in recent years become central to how the market operates, growing to account for about two-thirds of daily market volume, according to industry estimates.
The firms use high-powered computers to send "buy" and "sell" orders to the market at rapid speeds. High-frequency traders have said part of the value they add to markets is the liquidity they bring—being at the ready to swiftly complete a trade. Some of these firms have said that, were it not for them, the 2008 market declines would have been worse.