Sea Caves

The intertidal and submerged sea caves of the Berwickshire and North Northumberland Coast SAC are home to an incredible diversity of marine life. Caves are formed when weak spots in the cliff are eroded by the sea which creates tunnels and caverns. They vary in size from a few metres across to extensive systems. The types of plants and animals found in sea caves are influenced by several key factors including. Height on the shore will determine how long the cave is uncovered by the tide. The orientation of the cave will determine the availability of light and the amount of wave exposure and scour, as small boulders and stones are washed around the cave floor. These factors can result in a zonation of marine life in a cave as the conditions gradually change from light and exposed near the mouth, to dark and sheltered further inside.

Caves on the shore and in very shallow water experience strong wave surges and tend to have floors of coarse sediment, cobbles and boulders. This material is swirled around by waves and only animals resilient to scouring, such as limpets (Patella vulgata) and periwinkles (Littorina spp.) can survive. These invertebrates graze on lichens and microscopic algae. Colonies of mussels, along with barnacles (Balanus crenatus), ascidians such as (e.g. Dendrodoa grossularia) and purse sponges (Grantia compressa) may also be present depending upon the degree of scouring.
The zoned pattern of plants and animals in caves occurring on the lower shore often consists of a turf of algae near the entrance. The red encrusting algae – Audouinella spp. – can occur in dense red mats which trap sand. Further into the cave, the walls become dominated by a colourful burst of sponges, hydroids and anemones.

Subtidal sea caves are generally subject to less water movement and may accumulate silt or sediment on the cave floor. Deep water caves remain submerged by the sea at all times and are less affected by wave energy. Consequently, more delicate animals such as corals, sea squirts and jelly fish can survive here. These caves also provide shelter for a host of mobile creatures such as starfish, lobsters, crabs and fish, many of which may be white as they live in complete darkness.

Within the moderately exposed reef system of the Berwickshire and North Northumberland coast, the shelter provided by these caves is an important part of the ecosystem. Intertidal caves can be found in the sandstone cliffs to the north of Berwick, in the limestone at Howick, and on the north side of Lindisfarne. Submerged sea caves, tunnels and arches occur in the volcanic rock off the Farne Islands and at St Abbs Head .