Zonation is an integral part of ocean life. Environmental conditions such as light, temperature, salinity and pressure change with depth. However, zonation can also be seen without diving thousands of metres deep.

Tides are an astronomical phenomenon that shapes life on our planet, especially marine life. They deform the surface of the ocean, leading to sea level fall and rise along coastlines. Ebb drains the water level to low tide and flood brings it back to high tide. The difference between high and low tide can be several meters. The zone between the tide marks is called the intertidal zone and is the most compressed zonation of marine life. This is where on rocky shores you can explore the fascinating world of rock pools. The splash zone above the intertidal is a very harsh environment and often bare because it is neither fully suitable for marine nor terrestrial life. This is the domain of lichen, a symbiosis between fungi and algae.

Only very few marine creatures can survive the long exposure to the atmosphere in the upper intertidal zone. Characteristic inhabitants include barnacles, limpets and periwinkles. As one wanders towards the sea, this sparsity is incrementally replaced by the full splendor of marine life including mussels, crabs, starfish, anemones, octopus and seaweeds. Not only do tides determine the position of life, they also influence foraging and reproduction. Due to its diversity, the intertidal has inspired important literary works like Rachel Carson’s The Edge of the Sea, and John Steinbeck’s books including Cannery Row which were inspired by rambles between Pacific tides with his friend Ed Ricketts. In contrast to its beauty, the intertidal helps us comprehend the scale of anthropogenic sea level rise.

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