The Sound of Barra comprises a mixture of islands, extensive rocky reefs, sandbanks and shallow channels in a broad stretch between the southern end of South Uist and the north eastern shore of the island of Barra in the Outer Hebrides, off the west coast of Scotland. The range of subtidal sandbank habitat biotopes reflects the environmental conditions within the Sound. The area is highly exposed in the west (with highly mobile, impoverished sands), tide swept but reduced exposure in the mid-channel (increased diversity of fauna with some maerl) with deeper more sheltered areas to the east (stable fine sand with a diverse infaunal community). Moving further eastwards the sediment is gravelly with large pronounced ripples and small amounts of maerl. The southern part of the Sound is more sheltered and sediments are composed of fine sand with small amounts of silt. Sediment communities are variable in composition but are often dominated by algal mats in this southern part. The sea grass beds in the Sound generally occur on the sandy substrates in moderately exposed or sheltered environments and cover a large area although the density of the Zostera is often low. Maerl is also present over a wide area, located within deeper more, exposed environments of the Sound. Although the abundance of live maerl is often low, this habitat still provides a complex niche for a diverse group of species.
The Sound of Barra comprises a mixture of islands, extensive rocky reefs, sandbanks and shallow channels in a broad stretch between the southern end of South Uist and the north eastern shore of the island of Barra in the Outer Hebrides, off the west coast of Scotland. The reefs are most extensive in the western areas and, to a lesser extent, in the eastern parts of the Sound. The western part of the Sound is highly exposed with infralittoral rocky substrates dominated by tide-swept kelp forests Laminaria hyperborean communities, with a diverse associated fauna characteristic of accelerated tidal currents. There are also mixed kelp communities including Saccorhiza polyschides and Saccharina latissima in sand scoured areas. The depth in the site increases to the east, where shallower rock substrates also support kelp forests. Deeper rock surfaces are dominated by a turf of foliose red algae mixed with scour tolerant epifauna and with increasing depth there is an increased dominance of invertebrates similar to those of the shallower reefs. The intertidal rocky reefs support communities characteristic of a wide spectrum of exposure conditions. Exposed shores are dominated by the barnacle Chthamalus sp. with patches of small mussels, Corallina officinalis in the lower shore and a sublittoral fringe dominated by Dabberlocks algae Alaria sp.. Moderately exposed shores are characterised by a mosaic of the barnacleSemibalanus and Fucus vesiculosus and in the most sheltered shores are dominated by knotted wrack algae Ascophyllum nodosum .