It said why in the first minute of the video. The corals overcrowd each other on the reef killing some of them. So they go in and thin out the corals giving space to some corals and moving the others to the racks.
It said why in the first minute of the video. The corals overcrowd each other on the reef killing some of them. So they go in and thin out the corals giving space to some corals and moving the others to the racks.