Rocky reefs

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Rocky reefs - Paul NaylorRocky reefs - Paul Naylor

Rocky reefs that are exposed at low tide are great places to explore as there are many animals and some plants that can survive out of the water for some time. The presence of rockpools, crevices, and boulders increases the diversity of life because of the shelter provided.

What are they?

Rocky Reefs are fascinating habitats that are rich in life. Many marine animals and plants need to attach themselves to something solid for their survival. In the UK many of our rocky reefs are covered in a rich assortment of animals and plants. They act as important breeding, feeding and nursery sites for a great range of species such as fish and shellfish. In addition, they provide coastal protection by reducing the impact of waves upon shores.

The animals and plants that live between the high and low tide have to cope with a wide variety of challenges to the survival and live in an environment that is constantly changing. Many species occupy different parts of the shoreline based upon their adaptations and ability to cope with the rise and fall of the tides.

Where are they found?

Rocky reefs can be found widespread around the UK coast. They are found where rocks occur above or below the waterline. As the rocks are eroded by the action of water, cracks and holes appear which increase the availability of shelter for living things. Different rock types weather in different ways and may have different species.

Below the low tide mark rocky reefs can support extensive communities of marine plants which can form kelp forests. Reefs that are hidden from sunlight in deeper water, or under ledges, often have brightly coloured communities of invertebrates, which can rival coral reefs for colour and diversity.

Why are they important?

Rocky reefs, from the exposed high tide mark, down to the sublittoral (below the low tide) sections are teeming with wildlife. The intertidal rocky shore is an extreme habitat that is in a state of almost constant change when compared with the land or the sea. Because of water movements associated with tides, waves and spray, the conditions affecting different levels on the rocky shore vary continuously throughout the day.

Exposure to air is stressful to marine organisms just as submersion in water is stressful to terrestrial species. However, it is this dynamism which makes them special places for marine wildlife.

The constant disturbance by physical factors — such as wave action and sedimentation — and the activities of large, grazing predators — particularly sea urchins — creates intermittent barren patches, which account for the unexpected biological richness of rocky reefs. This ‘free space’ is continually recolonized by the larvae or juveniles of nearby adults or by the spread of local colonial animals. Competition for limited space among these recolonizers is fierce, resulting in a rich variety of different species.

Many of these species are at various stages of their lifecycles, each with different needs. The result is an incredibly dynamic ecosystem, with a high turnover of unsuccessful competitors. These unsuccessful competitors provide a rich food source for predators, which — in turn — attract ever-larger predators.