The tide coming and going twice a day constantly brings in objects that fascinate. Beachcombing provides endless interest and we may become absorbed looking for driftwood and artefacts both natural and man-made. Jellyfish washed up in vast numbers are beautiful when viewed close-up. The small common jellyfish reveals soft pinkish rings round its centre and does not sting. However, the large lion’s mane jellyfish has a powerful sting and its tentacles can become entangled in fishing nets, causing untold pain to fishermen as they haul them in. On shell-strewn Hebridean beaches, weird and wonderful goose barnacles float in attached to old ship’s timbers or discarded bottles. In the days before migration was properly understood, sailors thought that these elongated filter-feeding crustaceans were in fact emerging barnacle geese, since no one knew where the birds went, and certainly none had seen them breeding. Some even claimed to have witnessed the emergence of birds from these stalked barnacles. Though a beach is often our chosen destination, it is the rocky shoreline that provides the best habitat and encourages a far greater range of wildlife. The wealth of seaweeds in such a place provides enough moisture to protect large numbers of crustaceans, tiny fish and molluscs. The weed clinging on to the rocks is attached by a standfast or foot – a sucker that holds it tight to its anchor and enables it to remain there even in a heavy sea. Through photosynthesis, seaweed oxygenates the pools.

Life in miniature

Childhood memories of the rich rock pools round the rugged shoreline of the Ardnamurchan Peninsula, Britain’s most westerly point, still fill me with a frisson of excitement. After school and at weekends we would take sandwiches and bike to the shore. As the tide turned, an incredible world was revealed. A rock pool is one of nature’s miracles. A perfect aquarium replicating the sea in miniature, an oasis filled with life, from the tiniest phyto-plankton, and minute tendril of new green weed, to the birds and mammals at the top of the food chain. It is a fragile ecosystem subject to the constantly changing harshness of the environment. The creatures that live here have to be able to adapt as the water in their lagoon is changed twice daily.

Rock pools have always drawn me and I investigate them wherever I find them. However, none can compare with those particularly special ones of my youth. Hours were whiled away as we became totally absorbed, gently turning stones to see the wealth of tiny creatures underneath, and filling buckets with plant and animal life which we carefully put back before going home. We never noticed as our hands were grazed on the barnacles and became numb, and the salt stung the scratches we incurred. Nor did we care as we overstepped the mark, and the icy salt water filled our boots as we reached into deeper pools to unveil yet more treasure. We were simply oblivious to all the discomforts. The vivid colours of the plants and animals, the extraordinary, almost prehensile, worms and sea squirts, or the fascination of a hermit crab scuttling about in its borrowed shell, all proved intoxicating.

Providing we kept still we would watch enthralled as the crabs hid awaiting their next meal to pass by. Often we would go down to meet the Mull passenger ferry from Tobermory and wandered underneath the pier where huge succulent yellow-gold starfish clung on tightly, and the vast barnacle encrusted joists dripped with sodden fringes of emerald whiskered weed.

Turning stones

Recently I had the opportunity to take a young friend to Ardnamurchan on a flying visit to those very pools. And interestingly they, unlike so many influences of my youth, have miraculously remained intact, exactly as they were all those years ago. I found myself childlike once more as I saw the obvious delight and fascifascination of my young companion. He quickly became adept at turning stones in the gin clear water, and soon learnt to skirt round the rock overhangs to avoid startling the crabs and other creatures with his looming shadow. The best rock pools are those that retain sufficient salt water in them even during times of the lowest tides.

This enables a greater diversity of life to survive. In some areas where the pools are not so well covered, heavy rain can alter the salinity, which in turns changes the fragile ecosystem. When pools are unsheltered by rocks and the surrounding terrain, sun may also change the ecology as it beats down relentlessly. In the seaside environment, water evaporates quickly. With constantly fluctuating temperatures, the life therein has to be able to adapt; one moment the water in the pools may be tepid, but later it will once again be cold and hostile. An important feature of a rock pool is camouflage, and many of the creatures have colours and patterns to help with this. Fish blend perfectly with the weeds and stones that surround them – a sea anemone, a primitive member of the jellyfish family, has evolved to look flower-like. Its waving tentacles are stinging cells that immobilise prey as it passes.

Once the pools dry out then they close up their petallike tentacles to avoid both desiccation and predators till the water returns once more. Each new wave that sweeps over a pool will bring with it a nutrient rich soup to feed the creatures living in the rock pool ecosystem. Marine plankton is the first link in this complex food chain, together with microscopic worms and tiny jellyfish, copepods and minuscule crustaceans.

When rocks and stones are gently raised, sea urchins of all sizes are revealed, or perhaps common starfish, cushion stars, and brittle stars. The spines on the beautiful purple and green urchins are there for protection, and tiny protective spines may also be seen on the urchin’s close relative, the starfish. Sea urchins graze on a variety of weeds while the starfish eat mussels and other shellfish. The vulnerability of a rock pool cannot be overlooked. Increasing marine tourism and oil pollution can, and all too frequently does, wreak havoc. Litter, and toxic chemicals from farming and fish farming are also lethal, and our own interference may alter the delicate balance for the fauna. A rock pool is a pointer to the general health of the sea in that particular area. Introducing children to the world of the rock pool will open new doors and hopefully lead to a lifetime interest and desire to protect this, one of our most delicate habitats and one that deserves our utmost respect.