Many of the species in this genus occur in the Indo-West Pacific region and in the Tropical Eastern Pacific, where they are found in large numbers on the trunks, trees and prop roots of tropical mangrove forests a few metres above high tide level.
22.
Comprising three spans of 150 ft ( 45.7m ), it was 67 ft ( 20.4m ) above the high tide level . 12 ft ( 3.7m ) of the width of the bridge was reserved for rail and 23 ft ( 7m ) for general traffic.
23.
There have also been calls for a barrage across the River Usk to be incorporated with the M4 bypass, so that the level of the river would stay permanently at high tide level, although possible plans for a Severn barrage across the River Severn would reduce the need for a River Usk barrage.
