Forty new deepwater reefs discovered off the south-west coast have been described as 'precious hotspots of marine biodiversity,' writes MICHAEL VINEY
IN THE gliding beams of the spotlights, the reefs rise up like islands in a sea of creamy sediment, some of them to 100 metres high. Their base is a chalky rubble, but, travelling up the slopes, the lights find the first living coral – scattered bushes, then spiky thickets of white, pink and gold. In bitter cold and darkness, 300 metres below the ocean surface, these sudden, vivid gardens, thronged with life, take on an almost hallucinatory air.
Close up, the coral’s branches are misted with movement, as the tiny, reef-building polyps put out their tentacles to feed. The whole tangled fabric pulses with organisms – little crowns, cups, tubes, mats, fans and plumes of animals that look like plants, all feeding on particles carried in the swirl of currents. Among them climb squat lobsters, giant crabs and gleaming, spidery starfish, and above them swim fish like strange craft in the sky of a science-fiction city.
The first pictures from this month’s discovery of some 40 new deepwater reefs at the tip of the Porcupine Bank, south-west of Ireland, bear out the excitement of Dr Anthony Grehan and his team of Irish and French marine scientists aboard the Celtic Explorer, the Marine Institute’s research vessel. Its ROV (remotely operated vehicle) had found, said Dr Grehan, “by far the most pristine, thriving and hence spectacular examples of cold-water coral reefs that I’ve encountered in 10 years of study”.
It is exactly 140 years since chunks of the coral Lophelia pertusa, landed on the deck of the HMS Porcupine, a paddle-driven steam vessel carrying the scientist Charles Wyville Thomson out past the edge of the bank to dredge the abyssal bed of the Atlantic, more than 4,000 metres down. He was out to disprove the belief, general in the 19th century, that life could not exist in the deep ocean, far beyond the reach of sunlight. His haul of seabed ooze and coral fragments with its molluscs, echinoderms, worms and sponges, was confirmation that “life goes all the way down”. The nature and extent of the deep, cold-water reefs – hundreds of them clustered on the slopes of the continental shelf in a great arc from Spain to Norway – began to be realised in the 1990s, with seismic seabed prospecting for oil and gas reserves. Their extraordinary abundance off Ireland, notably on the slopes of the Rockall Trough and Porcupine Basin, was confirmed by the multi-beam sonar of the Irish National Seabed Survey.
Many of them started life thousands of years ago, anchored to the surfaces of rocks dropped by melting icebergs at the end of the last Ice Age; since then the reefs have built up on the debris of dead coral skeletons forming carbonate mounds. Indeed, the oldest dead coral branches have been dated to some 2.6 million years ago.
Unlike the sun-warmed corals of the tropics, nourished by symbiotic, microscopic algae, the cold-water corals and their invertebrate neighbours are largely fed by the fall of “marine snow” – fragments of dead plankton and other organisms drifting down through the water column. But while they might be insulated from the global warming that is bleaching and killing corals in shallow seas, they could still face long-term damage from man-made CO2 acidification of the ocean. This threatens the structures of all calcium-shelled sea creatures, including the corals.
More immediately, many of the reefs off Ireland have been ploughed by deep-sea trawling gear, or tangled with discarded nets and ropes. This is why Dr Grehan is urging protection of the new “province” of the corals – a cluster across some 200sq km as an EU Special Area of Conservation (SAC). It would add to four existing Irish offshore SACs that already protect coral mounds on 2,500sq km of seabed at the north-west and south-west of the Porcupine Bank and on the slopes of the Porcupine Seabight.
The EU and its scientists have acclaimed the reefs as hotspots of marine biodiversity, precious in themselves but also as feeding-grounds and reservoirs of species for the wider ocean. Among them are fish specially adapted to life in darkness or the twilight zone, with strikingly large and sensitive eyes for a world a-flicker with luminescent signals. Many species are eel-like or “rat-tailed”, their bodies tapering to a point to serve buoyancy in high pressure at the bottom of a heavy ocean.
Raised in huge trawls and suitably filleted, many strange-looking fish have been ending up as human food: not only rat-tails such as grenadiers but ferociously-fanged scabbard fish and small deep-water sharks. The long lives and slow reproduction of such species have brought a special urgency to halting a ruthless overfishing of the deeps.
The isolated and extreme conditions of the coral reefs now promise alternative human benefits. In total darkness, great pressure and temperatures down to four degrees, organisms have evolved that are highly unrelated to similar species elsewhere in the ocean, and with a different and exotic biochemistry. These are the target for new compounds for anti-viral or anti-bacterial drugs and new industrial technologies – a research strategy high on the Marine Institute’s agenda. Protection of the pristine, deep-water Edens is for nature’s biodiversity but also, as always, with human interests in mind.
Staff from the dept of earth and ocean sciences at NUIG will be giving presentations in the explorers tent at the Volvo Ocean Race on Monday afternoon
Ireland's Ocean: A Natural History, by Michael Viney and Ethna Viney, is published by The Collins Press