Rikoriko Cave, Poor Knights

Rikoriko Cave, Poor Knights

By Wade Doak

Reminding me of a bottle lying on its side half full of ocean, Rikoriko Cave must be one of the greatest sea caves in the world. No location at the Poor Knights affects me as deeply as Rikoriko, cave of echoes and dancing light. Topside its vastness fills visitors with awe, even terror.  The wave energy from the slightest surge excites this resonant sound shell with white noise.

At the neck of the bottle the entry foyer is high enough to clear my yacht’s mast top 15 metres above the surface. Within the main chamber the dome roof rises another nine metres. From the ceiling delicate ladder ferns dangle, seeking bounce light from the water.  A mauve tideline encircles the walls, and at low water this gives way to skirtings of yellow and red sponge.

Exploring the innermost sanctum (southwest corner) I was surprised to find that what appears to be streaky slime is actually a complex deposit of calcium carbonate in rills and whorls like icing on a wedding cake. Pigmented internally with algae, it is an abstract tonal artwork. Out by the eastern portal the water glows with a lovely turquoise radiance from light bouncing off the wall below.

A dive following the western wall from portal to rear is really a journey in to the abyss through a continuum of change. Diminishing light levels and food transport in Rikoriko Cave compress the living conditions of great ocean depths within the scope of one shallow traverse.

To document this I set out with Jan who carries a powerful movie light. I watched her swim in around the western entrance, passing a patch of tangerine sponge, a vertical fringe of kelp plants, and a small cloud of dainty butterfly perch. Just within the portal the upper wall is curiously eroded with thinly walled wave chambers, like cupboards. We glanced in one – a big speckled moray was in residence. Beside him two long white feelers waved. A cleaning station. Coral shrimp were advertising their services as surgeons. Their vivid colouration serves as a Red Cross symbol. No fish would eat a parasite picker, and the eel even let them clean its teeth.

As Jan finned along the wall of the entry hall eight metres down, the slope began to jut out into a complex of ledges and crags extending down to house-size rocks that rise from the bottom. At this stage the wall is spectacularly rich with delicate encrusting life, but until Jan illuminated the décor I only saw sombre shapes of muted colour. As the circle of light progressed an artist’s palette of brilliant hues glowed momentarily and receded to dimness as she passed. To dive these splendours without a torch is like exploring a shopping mall in darkness.

A brilliant orange sphere, segmented with white wedges glowed on sponge tapestry – a Trypneustes sea urchin from warmer climes. Long, delicate tubefeet waved beyond its short white spines. Thank goodness these vandals are sporadic visitors here. They climb kelp plants and gnaw through the stalk, wastefully severing the entire canopy.

Further along the  long sharp spines of a ruby red Diadema urchin bristled. Bulging on top was a mauve grape-like organ. The urchin stores its wastes in this sac. When full, it trips a valve and voids them clear of its body – a mini volcano.

As Jan swam towards the twilight, a retinue of wrasses followed. A leatherjacket busily inspecting the wall turned aside and rotated with gaping jaws. She passed over a huge flat rock elaborately carpeted with sponges of varying hues: orange, mauve, purple, red; each patch battling with its neighbour for dominance using subtle chemical warfare.

We could have spent hours exploring this region of the cave. With no wave violence and a supply of food transported by the oscillation of surges, the finest, most fragile of life forms adorns these rock surfaces. I once found a canary-yellow seahorse entwined amongst sponges that matched his colour perfectly. And photographer Glenn Edney discovered the lair of a tiny octopus with a coat of all the colours the spectrum allows.

Halfway into the cave, like an igloo entry, the hallway joins the sphere of the main chamber. This junction is a zone of turbulence. Swells see-saw along the wall and jostle on the corner. Nearby Jan lit up a big patch of brilliant yellow sea daisies or zoanthids with delicate circlets of 24 tentacles. These are really stalked corals that dispense with a calcerous house and settle on other creatures – an encrusting sponge or sea fan.

Rounding the corner to the right we entered another world. Light levels had fallen dramatically – we were on the edge of the abyss. As we travelled the curving cliff we noticed the effect of reducing food transport: less and less diversity until a bland region of tan or white knobbly, nodular structures predominated. Behind us the floor of the main chamber was a rubble field of boulders and rocks all similarly encrusted. But there were still some surprises. From the wall a massive yellow dinosaur’s foot with conical toes jutting out – truly a deep water sponge. On a small patch of sand I found a paper nautilus shell.

In the dimmest part of this giant dome Dr Tony Ayling discovered the fluorescent green solitary corals Paracyathus that hitherto had only been known from depths of around 1800 metres. In deep recesses and crannies crimson clusters of common cup corals are the main life form.

Rounding the cave’s innermost recess our journey along the eastern wall began. With a reverse slope that plunges 30 metres to white coralline sand, it supports a luxuriant forest of sea fans, all oriented at right angles to the prevailing water movement. Interspersed are massive vase and castle sponges, tube sponges like organ pipes, gnarled hydroid trees, pink lace corals, orange soft corals, and stunning carpets of jewel anemones.

Near the eastern portal within two deep recesses we found a range of creatures normally at much greater depths. Feather stars waved their spiral arms, gorgonian fans formed dense thickets, and in a slot there was another medical centre: a coral shrimp couple displayed their white feelers, awaiting customers. One carried teal blue eggs beneath her tail.

The darkest crevices swarm with big eyes, feeders of the night plankton. Close by clouds of demoiselles flit around the sunlight entrance, sapping up day plankton that swarm close to the vertical kelp forest.

A virtue of the Rikoriko wall journey is that there is no current to contend with, little need for decompression, no long surface swim, and you gain the experience of a whole series of deep dives without venturing deeper than 15 metres.

Stop Press…

This summer at the Poor Knights increasing numbers of yellow banded perch and black spotted groupers have been seen, along with more and more Lord Howe coralfish. With the tropical groupers, this could be reserve effect.


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