The seashore is a habitat that contains a wide range of microhabitats and ecological niches for different creatures. This is mainly due to the effects of the tides, that rise and fall twice each day.
             Tides are the vertical movement of water in a periodical oscillation of the sea, due to the gravitational pull of the sun and moon. The tides are on a semi-diurnal cycle, so there are two high tides and two low tides each day.
             Due to the orbit of the moon, the tides also have a monthly cycle. This creates neap (very low) and spring (very high) tides.
             The seashore can be divided into several zones, which are illustrated on the diagram below:
             This is the highest zone on the shore, and lies above the EHWS mark, and therefore is never covered by seawater. However, it may be occasionally be spray wetted. Because of this, it is mainly inhabited by terrestrial species, such as lichen, that can live in areas of very high salinity.
             This zone is the area that is covered and uncovered by the tides, and therefore organisms that live here must be able to tolerate a large range of conditions. It can be further divided into the Littoral Fringe and the Eulittoral zone.
             This part of the Littoral zone lies above the area that is completely submerged by the sea in normal conditions. However, it is frequently covered by splash from waves, and so is far more marine in character that the Supralittoral Zone. Lichens still dominate this zone, but some species of periwinkles and topshells may graze them.
             This zone is the area of the beach that is regularly submerged by the tides, and can be divided into three more zones, the upper, middle and lower shores. It shows the greatest species diversity of any of the zones.
             This region of the shore lies between the EHWS and MHWN marks, and so is only immersed during spring tides. Because of this, organisms that live here must be adapted to survive long periods of desiccation. The two seaweeds t...