Intertidal Biome

Intertidal Zone

The intertidal zone can be defined as the zone between the high and low tide mark.

Some of the hard conditions organisms in the intertidal habitat have to deal with are the ability to deal with both being submerged and exposed to the air, great physical impact of waves, desiccation, sunlight, the effects of freshwater during rains when exposed, lots of moving rocks and sediment in the water, and risk of predation both from predators in the water and on land.

Tidal background

The tides are formed as a result of the gravitational forces between Earth, the sun and the moon. Twice a month the three will be aligned as a result of Earth’s movement around the sun, and the moon’s orbit around Earth. When this happens the gravitational pulls will be the strongest and we will experience the greatest differences between high (flow) and low (ebb) tides. We call these tides Spring tides. On the contrary, the time half way between two spring tides, which occurs when we see the moon as half, the tidal difference will be the smallest, called Neap tides.

With this background it could sound like the size of the tide would only depend on the gravitational pulls between Earth, the moon and the sun, but this is not the case. The topography of the ocean bottom plays a great roll in how large the tide will be.

Different types and distribution

Intertidal habitats are found all over the world although the tidal range various extremely depending on location.
Some areas don’t even experience hardly any tidal difference at all. The west coast of Sweden in fact has a greater ocean surface level differences depending on changes in atmospheric high- or low air pressures, which has nothing to do with tides. On the opposite side of the Atlantic Ocean, in South Eastern Canada, we find the greatest tidal differences in world in the Bay of Fundy. Spring tides here create a 20m difference between high and low tides.

Adaptations by organisms

The type of organisms occupying the tidal habitat varies greatly depending on where we are on the planet. Temperate rocky intertidal areas will have totally different species than for example a tropical mangrove habitat. Coral reefs are also often affected by tidal differences, which may even totally expose the corals out of the water during low tides. The moving water exerts great demands on organisms in the area. If an organism lives on the substrate, it usually needs to have a way of either attaching itself to the substrate to prevent being washed away or being able to seek shelter. Barnacles settle and build a solid and permanently fixed structure on the rock. When under water, they reach out with a feathery appendage to strain the water for plankton and oxygen. When the tide goes back down, they close up the opening of the calcium structure with two plates to prevent desiccation and predation. Limpets are molluscs that stick hard to the rocky substrate by contracting the muscles in its foot and firmly grip the substrate. When times are not so rough, they use the foot to crawl on the substrate and graze tiny algae off the rock. Chitons are also mollusks with eight overlapping plates on their backs. The plates are flexible and allows the chitons to wrap around a stick to the hard surface with its muscular foot.

Life by the Tide

The Pacific inter-tidal zone is a harsh but beautiful ecosystem inhabited by creatures that developed bizarre and elegant forms in order to survive. The following film takes place during low tide on a foggy summer day when the sea pulls back from the land, exposing the peculiar life below. Winner of the 2009 International Wildlife Film Festival awards for Best Amateur Film and Best Music Video.