The UK’s expansive coastline, which is well over 6,000 kilometres long, varies dramatically and presents a number of different rocky habitats, ranging from calm, sheltered coves and rocky beaches to tall, imposing cliffs. Within each of these rocky habitats the conditions are highly dynamic, due to the ever-changing tides (1) as well as additional environmental factors such as temperature and wind (2). Rocky shores are formed when waves erode softer rocks, leaving harder rocks exposed (3).
Marine habitats are often divided into several zones, which are based on their position in relation to the tide. The sublittoral zone is the area of the shore which lies below the low tide line, and is therefore permanently submerged. This is the most stable environment within a rocky shore habitat, and also one of the richest, sustaining an abundance of different marine species (4).
The intertidal zone is the area between the high and low tide lines which is intermittently submerged or exposed to the air depending upon the position of the tide. Areas closer to the sea are the first to be submerged as the tide rises and the last to be exposed as it ebbs, and therefore spend a greater proportion of time fully submerged. Species present throughout the intertidal zone must be able to survive both in and out of sea water (4), and they vary in form and function according to their distance from the sea (2).
As the tide goes out, pools of seawater remain on uneven rocks. Rock pools are temporarily separated from the sea, with the pools further away being isolated for longer. The conditions in these small microhabitats are often harsh, with evaporation and rain causing the concentration of salt in the water (the salinity) to fluctuate dramatically. The temperature and oxygen levels can also vary immensely depending on sun exposure and plant activity (5). Species that live in rock pools must be able to cope with an ever-changing and often relatively extreme environment (5) (6), yet the pools frequently sustain a host of plants, crustaceans, anemones and fish (6).
Seaweed and other marine debris is deposited at the point reached by the highest tide (7), called the springtide (4), forming the strandline. This plant matter supports a variety of small invertebrates, which in turn are prey items for larger animals such as birds and small mammals (7).
Further up the shore, the splash zone is the area above the high tide point that is rarely, if ever, submerged by the water, although the rocks will occasionally be soaked by wave splashes. This harsh environment is unable to sustain as much diversity of life as the areas closer to the sea. However, some species such as lichens and sea slaters are able to survive there (4).