Habitats

The rocky foreshore

The foreshore is an intertidal zone, exposed at low tide and submerged at high tide. We talk about the rocky foreshore when referring to areas of durable, friable rocks, which may also contain sand, which is brought there by the currents, during tidal cycles.

The rocks are shaped by the climate and the animal and vegetable organisms that live in them. Fluctuations in salinity, sea spray, and the great differences between the temperatures at night and during the day can erode the rock and change its aspect. When water flows over the rock it can crack it in places where it is most fragile or where there are pre-existing faults. As the rocky surface is not homogenous, its nooks and crannies provide many places for organisms to hide and protect themselves, while the flat parts allow others to gain a firm foothold. In the latter case, it is also possible to discern the places where organisms were attached as they often leave visible marks.

The organisms that live on the rocky foreshore have a good way of attaching themselves so that they are not dragged off by the tides. Limpets and barnacles need a rock that is regular enough to allow them to attach themselves without any daylight showing between the rock and their shell. Algae bind about them with a clamp. In order to avoid drying out at low tide, some organisms secrete mucus in order to maintain their required humidity level. For example, if a limpet cannot seal itself hermetically to the outside during low tides, it will lose its water reservoir and dry out. That is why its shell is perfectly adapted to the rock on which it is found.

Sand and shingle beaches

Beach sand, is a very general term to refer to particles that are more or less fine. These particles are classed according to their granule size (the French classification shown here is only gives an indication, as there are other scales:

• Vase / Argile [Clay] => particles with a diameter of less than 0.06 mm
• Sables [Sands] => particles with a diameter of between 0.06 mm and 2 mm
• Graviers [Grits/Gravels] => particles with a diameter of between 2 mm and 1 cm
• Galets [ Pebbles] => particles with a diameter greater than 1 cm

The species present on sandy and gravel beaches are very different, as these two environments differ greatly:

Sandy beaches - Even if the beach seems deserted when seen at low tide, this is just an appearance: a number of organisms are nestling there in order to avoid desiccation (water loss, drying out), as well as variations in temperature and salinity [salt levels]. It is at high tide that this life can be seen. On the supralittoral stage, and most particularly near to piles of algae deposited by successive tides, we can see sea roaches [ligia].

Pebbly beaches - A pebbly beach is made up of fragments of rocks with a particular form: they are very smooth and rounded. This outer appearance is the result of the repeated action of water, bad weather, friction, and of the waves, which has polished and shaped them.