Various geographical reasons can be given to explain why the marine life at Lundy is a little different from that of the adjacent mainland coasts and why different seabed habitats are present around the island. The main reasons are set out below.
The island’s location in south-west Britain
Western coasts of the British Isles are influenced by relatively warm water brought across the Atlantic by the Gulf Stream (also known as the North Atlantic Drift), originating in the Caribbean and the Gulf of Mexico. The island also lies at the northern extreme of the Lusitanian Province, which includes the warm temperate waters of the Mediterranean, the Azores and the Canary Islands. Thus, colourful species which have their centres of distribution further to the south can be found at Lundy, such as the pink sea fan Eunicella verrucosa, the sunset cup coral Leptopsammia pruvoti or the golden kelp Laminaria ochroleuca.
The island’s position in the Bristol Channel
Being an island lying some way off the mainland coast, Lundy’s marine life benefits from being bathed in clean oceanic water more often than in murky coastal water. This means that the island avoids the worst of any pollution that might emanate from mainland sources, such as from sewage outfalls or from agricultural run-off. In times past though, it has had to cope with the impacts of activities such as sewage sludge dumping and of marine gravel extraction.
The island’s geology
The island we see today consists largely of granite, some 52-59 million years old, with a small appearance of slate in the south-east corner. In geological terms, the island is relatively young when compared to the granite exposures of Exmoor and Dartmoor which are over 300 million years old. The granite intrudes into metamorphosed sedimentary rocks with a swarm of dykes cutting both granite and sedimentary rocks. The dykes, which are mostly dark-grey dolerites, are up to 2.3 m wide and are important for marine life as they are the places where caves often form and may create subtidal rock walls (Hiscock & Irving, 2012). One of the basalt dykes forms an impressive vertical face that can be seen to the south of the Castle.
The island’s orientation
The island has a north-south orientation, which means it acts as a breakwater to the tidal flow up and down the Bristol Channel. On flood tides (as water moves up the Channel), the current splits in two to pass around the north and south ends of the island. The opposite occurs when the tide is ebbing, some 6½ hours later. Both of these water movements create strong tidal races around each end of the island, giving rise to high energy conditions. At times of spring tides, the flow of water in these races can reach 6 m/s. The resulting turbulence provides strong-swimming fishes an opportunity to feed, which in turn attracts porpoises and dolphins to feed on them. Off the north end of the island, vertical rock surfaces are covered with colourful jewel anemones which thrive in such conditions.
The island’s intertidal and subtidal habitats
Prevailing winds are from the west/south-west which leads to the rugged west coast being exposed to pounding waves during westerly storms. This results in the shores here being dominated by hardy, well-protected organisms such as barnacles and limpets, with very few seaweeds apparent. By contrast, the east side of the island is relatively sheltered. Here the shores are dominated by a rich variety of seaweeds, harbouring many animal species characteristic of sheltered rocky shores.
Granite bedrock extends for at least 1 km off the west coast, its disappearance marking the western boundary to the MPA. Here can be found rocky outcrops with gullies in between, with a diverse array of sponges, pink sea fans, potato crisps bryozoans, sea urchins and sea cucumbers. The calmer water off the east coast allows for silt to settle out of suspension and onto the seabed, leading to extensive areas of mud gradually building up. Such soft sediment allows burrowing animals to take up residence such as angular crabs and red band fish. Subtidal bedrock may be covered by lush hydroid-bryozoan turf, clusters of red sea fingers and yellow cluster anemones.
Within the MPA, special protection is given to the following habitats: intertidal and subtidal reefs; shallow sediment seabeds; and submerged or partially submerged sea caves.
The following species are also afforded special protection(1-3): common dolphin Delphinus delphis1; bottlenose dolphin Tursiops truncatus1; Risso’s dolphin Grampus griseus1; harbour porpoise Phocoena phocoena1; minke whale Balaenoptera acutorostrata1; long-finned pilot whale Globicephala melas1; grey seal Halichoerus grypus2; basking shark Cetorhinus maximus1; pink sea fan Eunicella verrucosa1; and spiny lobster Palinurus elephas3.
- 1 Wildlife and Countryside Act, 1981
- 2 Protection of Seals Act, 1971
- 3 Marine and Coastal Access Act, 2009
