Tales From The Tideline

Forest and Bird, Issue 291, 1 February 1999, Page 44

Tales From The

Tideline

—Anne Graeme.

ANN GRAEME

ew things are more pleasant than a on the beach — the dance and sparkle of the waves, the sand crisp under foot, the sharp freshness of the air. ‘Smell the ozone, people say, but really it is the tang of seaweed and spray. And to top it off, there is the pleasure of scanning the tideline for the debris of the previous tide. Here you find the treasures cast up by the sea, clues about the life out of sight, under the waves. Regrettably you find rubbish too, the thoughtless debris of the smartest animal on Earth. I carry two bags, one for rubbish and one for treasure. Shells are the houses of the myriad species of molluscs that live in the sea. OT = The single shells of tuatua, cockle, morning star are really half shells, for these are bivalve or ‘two-shell’ molluscs, having two ‘wings’ hinged together to make a container protecting the soft body of the shellfish. When they wash up on the beach, seagulls and sea lice feast on the soft bodies and the empty shells break apart at the hinge. Many bivalve shellfish live burrowed in the sand, the shells ajar to allow the feeding tubes to push up to the surface. The tubes strain the plankton from the sea water — a life of monastic simplicity compared to their roving relatives, the garden and sea snails. Some shells on the drift line have holes drilled right through them, so round and neat that the shells are ready to be strung into a necklace. But

no human drilled these holes. An inoffensive looking snail called a whelk twisted its rasping tongue back and forth to slowly erode a perfect hole through the heavy shell. This is a long job, but it will be a big feed for the whelk. It is careful not to kill its prey immediately, or the shells would gape open, letting the food smell escape and attract other scavengers. Instead, the whelk squeezes its thin proboscis through the drilled hole, first sucking

up and digesting the less vital organs of the unfortunate shellfish, then slowly consuming the rest of the living animal. The children’s favourite is the cat’s-eye, not an entire shell but the robust, protective ‘stopper’, or operculum, of the cat’seye snail. Another favourite is the little fan scallop, coloured orange, purple, cream or yellow. The fan scallop lives attached to the underside of rocks. Camouflage doesnt matter in these dark recesses, which may be why the shells are so varied and colourful.

It is after a storm that the private life of the sea is most exposed. Seaweeds torn from the rocks bring up on their ‘holdfasts’ little communities of sponges, tubeworms, mussel’s beard (small, sea anemone-like creatures), goose barnacles and shells. Shells, dislodged from the shelter of the sea bed, carry barnacles, strange egg cases and even hermit crabs. The scavenging gulls have a busy time but the next tides wash away the carnage of the storm. Fragile shells are broken by the pounding waves but some survive, and are blown higher up the beach against the dunes. Here you will find the delicate ram’s horn shell, so thin you can see right through it. It seems a miracle that it is undamaged, but this shell has only briefly seen the light of day, having been hidden inside the body of a little squid. Hold up the shell to the light and you will see that it is a coil of separate chambers, connected by a central tube. Just like a diver uses a buoyancy jacket, the squid can adjust the volume of air in the chambers and float effortlessly at the depth it chooses. Ram’s horn shells are often washed ashore in huge numbers. This tells you that far out to sea, driven by the primaeval influences of the seasons and the moon, squid have come into breeding and thus to the end of their short lives. On northern beaches you will find the violet snail shells, whose exotic

beauty is matched by a life story worthy of science fiction. No humble life crawling on the sea floor for these snails. Each builds itself a raft of strong bubbles. Then, like a pirate ship, the snail drifts in the ocean currents. Also drifting in the currents are other pirates, jellyfish like the Portuguese man-o’-war and the _ by-the-wind sailor, catching passing prey with their stinging tentacles. But catching a passing violet snail is a fatal mistake for them, as, immune to the stings, the snail consumes the jellyfish, and adding insult to injury, incorporates the purple jellyfish pigment to colour its shell violet! With the changing tides, every day is different on the shore. A walk on the beach offers us

beauty and inspiration and a chance to share the secrets of the sea.

is

national co-ordinator of the Kiwi Conservation Club, Forest and Bird’s junior arm. She lives in Tauranga.