Lessons by the sea

Spending a day on the coast or beach can be a great nature lesson on “the Intertidal Zone and Adaptations of the Marine Life”. Sandy beaches tend to be more popular with families with young children and teen beach bums. In Japan, going clamming (to get littleneck clams) with a bucket is a popular outing especially for families with little ones. But a rocky beach with lots of tidal pools is best for observing marine life forms.

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We visited Jogashima’s beaches several times from spring onwards and discovered that when we timed our visits to coincide with low tide, we were able to see the widest range of zonation from the high-tide line to the water’s edge.
At low tide, we were able to see the greatest numbers of marine life and shells since the low tide allows us examine the creatures that live down near the low-tide line (creatures that are barely able to withstand even a short spell out of saltwater) all the way to those living up near the high-tide line are able to withstand long periods exposed.

The intertidal zone

The intertidal zone is inhabited by an amazing variety and number of organisms. It is a harsh environment where living organisms get battered physically by the constant wave action that wears and washes at the shore as they live according to the rhythm of the rise and fall of the tides.

This is where the important concept of adaptation comes into play:

  • Any organism living here must be able to hold on tight, and withstand this battering by hiding away in cracks and crevices. A limpet is safe at home in a protected rock crevice, or in its well-worn socket on a less exposed rock (while a clam burrows into the sand).
  • To survive it must also endure the changes in temperature and salinity. A submerged home site is often first exposed to air and is then baked or boiled under the sun.
  • The sucking foot adaptation: E.g. limpets – a conical limpet clamps its shell on an exposed rock with its massive foot sucking itself down hard against the wave action – many times we tried prising limpets off the rocks, and it was near impossible even using another rock as a tool.
  • Burrowing action. Along more sheltered shores, muds and sands are more stable and form a soft habitat and home to very different organisms. Many of the species living in this kind of soft habitat are burrowers, delving to differing depths to avoid the fluctuations that come with the daily tides. For example, a clam or cockle finds safety by burrowing into sand or mud.
  • Look for creatures with protective armor adaptation: E.g. barnacles – burrowing is out of the question for species making rocky shores their home, unless they can find a crack, or crevice, or a rock to hide beneath. So many creatures take a medieval knight’s approach — heavy, protective armor so they can face up to the worst that nature’s waves can throws at them. Most of the immense array of mollusks secrete some sort of protective shell: the limpet has a conical one, the whelk, a spiral one or the bivalves (mussel or clam) have shells in two halves. In each case, the shape of shell was evolved as an adaptation to the mollusk’s environment.

Collecting seashells has been a popular past time for generations of kids … take your shell collection further as a lesson in taxonomy – label your shells and find scientific and common names for them. They make lovely displays for the bathroom / changing room.

The sea or ocean, the marine life found in it and the food chain are common topics for nature science studies in schools. Take it further … have a seafood meal and identify the kinds of sealife we are dependent upon, read a book and discuss the different habitats and zones for fishes and other forms of marine life. In Japan’s southern islands from Amami Oshima to Iriomote-jima support mangrove forests. We can teach the importance of these mangroves and other coastal wetlands as endangered but vital places where many forms of marine life receive shelter before they begin their journey out in the open sea.

Coastal topography lessons

Other lessons from nature can be gained by looking at the coastal topography as you take your walks on the shores.

Active shores, exposed to strong wind, waves, and surf, give us dramatic landscape features to look at and to explore. Lessons on erosion, wave action and currents can easily be combined with beach excursions. Sand and shingle beaches fronted by bays or lagoons make good opportunities for lessons on currents, wave direction or energy. Volcanic bluffs and jutting cliffs make good geology lessons. Discuss the impact of the weather and seasons on the coasts. Around northern Japan, exposed shorelines in winter will freeze. Even as the tide recedes, ice forms on the shore, and in some areas solid masses of floating drift ice bulldoze their way ashore. These forces of change shape both the coastal environment and the organisms that can live there.

Living in the Japan, there is little excuse to miss a nature lesson by the sea … there are after all 29,750 kilometers of coastline … and the sea is never more than 200 km from anywhere in Japan.


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