Black Coral


By Roger Grace

Black Coral

In my early days of diving at the Poor Knights in the mid-1960s, black coral was common in deep water. Our deep dives on air would not be approved of today, but by spending lots of time in the shallows using up the last air in our tanks we avoided getting bent. We stayed in the shallows a long time more through a passion for diving and looking at the rich life on the walls than through any conscious bend-avoidance plan.

Now I would never advocate all of our diving practices of the 1960s. I am convinced, however, that those long ‘safety stops’ which were built in to our dive routines kept us safe from gas bubbles, but narcosis was another matter.

One day we found the largest black coral tree I have ever seen. On the shortest day of the year in 1969, fellow students Tony Ayling, Barry Russell, Ian Briggs and I joined Wade Doak on a trip to the Pinnacles on Fred Cotterill’s boat Matira. It was one of those magic winter days with clear blue skies and flat calm seas.

Fred anchored Matira off the northern tip of the Pinnacles, on an underwater rock only 30 metres from the cliff. Fred used a small home-made grapnel on a rope – no chain, and barely more warp than the depth of water in which he anchored. Fred’s unique anchoring technique worked.

We swam to the cliff and dropped through clouds of demoiselle, exploring a new site we believed no-one had dived before. This was how most of the good spots at the Knights were originally found.

The sheer vertical wall was featureless till near the bottom. We could see a ghostly-white shape materialising below us. A huge black coral tree sprouted from a small rock at 210 feet! This tree was so tall we measured it with our depth gauges – close to 20 feet! (‘feet’ were our prefered units on dives in those days).

In the top of the coral tree perched a John dory, with black and white wavy stripes running along the sides. I approached closer and closer, taking several shots with my Nikonos II and black and white film – a classic photo which was used a lot in those days.

Three months later we were disappointed to learn that the huge black coral tree had gone. Probably several hundred years old, the spectacular giant was likely ripped off by unscrupulous divers, or perhaps innocently by an anchor (but I don’t believe so!) Those were the days before black coral was protected by law. Commonly divers’ wives or girlfriends sported black coral jewellery – pendants or ear-rings made from the ebony-like skeleton of the coral colony.

A friend of mine at the time had his attic filled with black coral trees, in anticipation of making black coral jewellery for a retirement income. But then a law change protected black coral, making it an offence to take or possess the stuff. So the coral in his attic became a white elephant. Black coral and red coral are now totally protected under the Wildlife Act.

To his credit, although he was a diver he did not collect black coral himself. His collection came solely from trawlers working mainly in the Hauraki Gulf! We can only guess at what damage was done by early trawlers to high-profile sealife growing on small rocky patches throughout the Gulf. ‘Oasis communities’ is the modern term – where rich assemblages of black coral, gorgonians and other corals, abundant sponges and a host of smaller invertebrate life occupied low patch-reefs. Trawlers used to work in pairs dragging a thick wire strop over the seabed to flatten any obstructions so they could later trawl safely over the area!

To find black coral it was usually necessary to dive to at least 180 feet. There were a few shallower colonies, for example one at 160 feet near Rikoriko Cave. But to see several together you had to go to 200 feet or more. There was a wonderful spot where a horse-shoe shaped ‘amphitheatre’ on the side of a deep pinnacle had 20 black coral trees bristling from the walls at 220 feet – now definitely the realm of tech diving!

On a day when the water was particularly clear, Wade Doak and I swam down the western side of the Sugarloaf. Hovering beside the cliff at 160 feet we surveyed an awesome scene through a school of splendid perch. The cliff continued vertically to 220 feet, and then a slope of large boulders ran away to the sand at what I guessed was 270 feet or more. That boulder slope was dotted with dozens of black coral trees – at least 50 within our field of view!

The most accessible black coral tree was at a mere 125 feet deep on the southern tip of Serpent Rock. I often visited it when I wanted to show someone black coral. But then in 1983 something terrible happened. A heavy plankton bloom, spawned by a strong El Nino year, completely killed all the black coral at the Poor Knights.

My next visit to the Serpent Rock coral tree revealed a dead black skeleton. Since then I have never seen a healthy black coral tree at the Knights. More recently the Serpent Rock coral skeleton became colonised by dozens of fluorescent jewel anemones, fluffy hydroids and bryozoans, and to my amazement two small patches of live black coral! I doubt that these are living remnants from the original tree. They are almost certainly a result of new larvae settling on the old skeleton.

Now if you want to see black coral Fiordland is the place to go. Because of the heavy rainfall (eight metres per year!) and calm conditions in the deep narrow fiords, a freshwater layer floats on the surface. This is stained by tannins and dyes leached out of rotting leaves and peaty deposits on the forest floor. The brown freshwater layer severely reduces light penetration to the clear seawater below, creating conditions for marine life in the Fiords similar to that in much deeper water offshore. Consequently normally deep water animals can be found in shallow diving depths.

In Fiordland, you can snorkel to black coral in six metres of water! Whole walls of black coral are accessible in only 20 metres. The best groups and largest trees are usually on the ends of points, where they are protected from occasional rock-slides which tend to fall to either side of the point rather than over the end. This gives the corals a chance to grow to a large size at their slow rate of less than 100mm per year.

Black coral does best in a gentle current, supplying plankton for tiny stinging tentacles on the anemone-like polyps. Nearly all black coral colonies have snake stars entwined around the branches. They come in several colours – reddish black, black with white stripes, and bright yellow. They don’t eat the coral, but at night clean detritus from the branches.

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