How much of corals' nutrition comes from hunting?

When it comes to feeding, corals have a few tricks up their sleeve.
Most of their nutrients come from microscopic algae living inside
of them, but if those algae aren’t creating enough sustenance,
corals can use their tentacles to grab and eat tiny prey swimming
nearby.
Source: FS – All – Ecology – News 2
How much of corals' nutrition comes from hunting?