Multibeam echosounders to map a reef
The reefs at Mingulay were discovered using a multibeam echosounder secured to the hull of the RV Lough Foyle in the summer of 2003 (see Mapping and View Location in Google Earth for images). By carefully going through historic coral records back to the mid-eighteenth century and using the available charts of the seafloor, researchers selected areas of the seabed with steep slopes where exposed rocks or piles of stones dropped by retreating icebergs thousands of years ago may have provided a perch for corals to settle and grow.
With limited time and money, the 2003 surveys had to focus in just a few areas and produced a series of multibeam maps showing not just the shape of the seafloor, but also something about its texture from strength of the acoustic return (the so-called ‘backscatter’).
The first area surveyed, till this day known as Mingulay Area 1, was immediately exciting – there were many lumps and bumps concentrated in one particular area and extending along a ridge that cut right across the seabed. As soon as video cameras were lowered onto this area it was clear that these lumps and bumps were in fact a whole series of Lophelia coral reefs, some growing more than 5 m above the surrounding seafloor (see Coral Reef Mounds Location for images). But why were there corals here and not in other areas? Why were they growing on the flanks of this large seabed ridge?
Figuring this out meant understanding the water flows - known as the hydrography - of the area.