By Tony and Jenny Enderby
Small fish swirl in front of us and crabs scuttle across the sand. Shrimps with bulging eyes duck back into their perfectly-circular holes. A piece of green codium seaweed drifts past in the incoming tide. It has a tiny passenger – a bright yellow seahorse.
Everywhere small snails move across the sand. Some have their original inhabitants but others move much faster with new owners, hermit crabs, that stop and peer at us from underneath the shells.
We are drifting with the tide in the Whangateau Harbour, an hourâs drive north of Auckland, New Zealand. The water temperature in the estuary exceeds 25ÂºC in summer. The clear water, fish schools and invertebrate life almost gives the impression of an aquarium. Large numbers of fish come in with the tide and school around the estuary. Yellow-eyed mullet, kahawai, snapper, goatfish and even the occasional predatory kingfish cruise in.
The normal residents: parore, flounder, goatfish, stingrays,
eagle rays and eels, come and go around us; sometimes in large numbers, other days hardly seen.
As we drift over the sandy bottom, flounder move rapidly away leaving trails of sand then stop again, almost invisible, a metre or two away. They are masters of camouflage. We approach slowly as one lies partly buried in the sand, eyes protruding, staring blankly, pretending to be just part of the sea floor. I brush the leaves off its back and it doesnât move, allowing me to take close up photographs. Smaller sand blennies, only a few centimetres long sit with their pale colour blending perfectly, inspecting what weâre doing.
Beneath the sand is the realm of the bivalve sea shell communities: cockles, pipis and wedge shells. Their breathing siphons protrude from the sand. Mounds of whelks pinpoint the demise of a fish that theyâre feeding on. Further out, at the edge of the visibility nearly 15 metres away, larger fish are just shadows.
A large part of the harbour is home to millions of cockles. These edible bivalves measure up to five centimetres in diameter and are found by digging just under the sand. Rather than over-collecting the biggest danger to the cockles is from excessive silt that could wash into the harbour after heavy rain.
Amongst the cockles are the largest and most aggressive crabs, the swimming paddle crabs. I follow one that dashes away and buries itself, leaving only eyes protruding. At night Arabic volutes, the estuaryâs largest gastropods, with dark brown lightning patterns against a tan background, surface to hunt. The purple and yellow animal rapidly drags its 15cm shell below the sand when disturbed.
Spider crabs, resplendent in a coating of hairs scuttle across the sand and settle, becoming almost invisible. They adopt a threatening pose, white nippers pointing upwards to ward off these giant intruders into their domain.
Crabs and shrimps, move in and out of their burrows as we pass. The only sound is the constant cracking from the shrimps snapping shut their claws. Occasionally a mantis shrimp emerges from its hole, grabs food, and quickly darts back to the safety of its home. Some are translucent while others have red and green markings down their backs.
Closer to the mangrove trees the sea floor becomes a moonscape with pneumatophores, the aerial breathing roots of the mangroves, pointing upwards. The surface reflections ripple on the sand creating unusual patterns amongst the forest of air roots. Patches of Neptuneâs Necklace seaweed lie scattered around, providing havens for more tiny marine life.
Mangrove is a name more synonymous with swamps rather than a place to snorkel. The mangrove forests closer to the city have become muddy with little visibility because of silt, fertiliser and run off from subdivisions and stormwater.
Most people are surprised to learn that the water in the harbour is usually much clearer than the open coast. The reason is the huge number of filter feeding animals that live in the harbour. The bivalve molluscs, barnacles, anemones, crabs and tube worms combine to act as a giant filter. They strain the minute plankton particles from the water leaving it much clearer. The sub-species name of the local mangrove, Avicennia marina resinfera was a reference to the lumps of kauri gum or resin often found in mangrove estuaries and incorrectly attributed to the mangrove trees.
It was only recently that the importance of mangrove areas became known. The bottom end of the food chain starts with microscopic larvae. Larger animals feed on these and on up the chain to the larger fish predators such as snapper.
Small mud crabs and brilliant blue half crabs with their filter feeding mechanisms nestle among the mangrove branches. Other crabs climb along the branches of the mangrove trees, racing around to the opposite side of the trunk as we near. Schools of parore, yellow-eyed mullet and tiny kahawai move in and out of the branches. If we move too fast they vanish into the branches and hover near the trunk.
Peering in we can see the sunâs rays sparkling down through the branches creating a magical scene. The light reflects off the little fish as they dash for cover on the far side. Rather than just somewhere to get into the water when the coast is too rough the mangroves are now somewhere worth a look in their own right.
Weâve been in more than an hour now, the tide has turned and the visibility is dropping. The gentle current will carry us back up the harbour to where we entered. Maybe weâll see something different as we cruise back but with water as warm as this, thereâs no hurry.
The best time to snorkel in the harbour is after at least a week without rain. Any downpour leaves a layer of fresh water on the surface above the salt water, causing a strange blurry effect.
The hour prior to high tide has the best visibility and higher tides, around the full and new moon, have greater flows of water providing clearer water.