It appears that, with multiple exchanges, the closure of some markets may just increase the reliance on more peripheral, less liquid alternatives. The traditional specialist on the floor of the NYSE is no longer a backstop to prevent a collapse in price.
But all of this changes market microstructure in insidiously destabilizing ways. For the first time we have large providers of this shadow liquidity, algorithms and high-frequency sorts, that individually account for large percentages of daily trading activity, and, at the same time, that can be turned off with a switch, or at an algorithmic whim. As a result, in market crises, when liquidity was always hardest to find, it now doesn't just become hard to find, it disappears altogether, like water rushing out sight via a trapdoor to hell. Old-style market-makers are standing aside as panicky orders pour in, and they look straight at shadow liquidity providers and say, "No thanks. You battle bots take it". And, they don't
The FT on algorithmic trading.
The FT looks at the regulatory impact.
Larry Tabb, chief executive of consultancy The Tabb Group, says: “We really need to step back and think about centralisation versus fragmentation and who is providing liquidity. It opens the up market to a whole series of questions about how we want our markets to function.”