Why are there cold-water coral reefs at Mingulay?

The answer to this question took the joint efforts of scientists from several countries working together through the European HERMES project. Although shallow by deep-sea coral standards, the reefs at Mingulay are still too deep to study by diving and too remote for daily visits by a research ship. So how do you build up a picture of life in the Mingulay Reef Complex?

The answer is by using deep-sea landers that sit within the corals for up to a year recording information about their environment. The landers used at Mingulay were built by the Royal Netherlands Institute for Sea Research (NIOZ) who brought their research ship RV Pelagia to Mingulay in 2006 and 2007. The landers were equipped with current meters and optical sensors and set down carefully amongst the coral reefs.

The current meters on the landers gave researchers the first idea of the world experienced by Lophelia in its natural habitat within the Mingulay reefs. Even at depths of over 100 m, the corals still feel the effects of the tide. At Mingulay Area 1, the first area mapped in 2003, there was a strong pattern related to these tides. Every six hours the corals are washed by warmer water coming down from the surface. As well as being warmer, the water contained more plant plankton (or phytoplankton) – this was detected by the optical sensors because the pigments in the phytoplankton fluoresce.

By working with specialists in the physics of water flow, the researchers worked out that the corals were growing on the flanks of the large rocky ridge because the ridge interrupted the wave-like flow, creating turbulence and causing foods-rich surface waters to wash down across the seabed. Time and tide wait for no man, and every six hours the corals at Mingulay can expect a dose of warm, food-rich water.

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