Environmental Engineering Reference
In-Depth Information
MARINE CAVES
Marine, or littoral, caves form special environments within rocky shores and Britain has the most varied
and extensive sea caves on the Atlantic coast of Europe. The communities present in caves vary consid-
erably depending on the structure and extent of the cave system, the degree to which they are submerged
and the exposure to scour, turbidity and surge, and their geology. Although the walls and roof are con-
structedofhardrock,thefloorofthecavecaneitherbesoftorhard.Cavesontheshoreandintheshallow
sublittoralzonearecontinuallysubjecttowaveactionandthereforetendtohavefloorsofcoarsesediment
and boulders that move and scour the inside of the cave. In Gower there is a high sand table and much
of the inside of the marine caves, such as Bob's Cave under Mumbles Head (Fig. 63), tends to be worn
by sand and therefore inhospitable to animals and plants. Where there is less sand, caves are typically
colonised by encrusting animal species, and often support shade-tolerant seaweeds in the 'twilight zone'
near their entrances. The caves themselves vary in size, from only a few metres in depth to more extens-
ive systems, which may extend a considerable distance into the rock. While the Countryside Council for
Wales has carried out several surveys of sea caves along the North Wales shoreline there has yet been no
similar survey ofthe Gower coast and it is quite likely that a number ofsmall, but species-rich, caves will
be discovered by divers.
Caves in deeper water are subject to fewer disturbances and may have silt on the floor. The sponges
Dercitus bucklandi and Thymosia guernei , solitary ascidians, bryozoans and the sessile larvae of jellyfish
are characteristic of these deeper caves. Small deep caves also provide shelter for crabs and lobsters.
FIG 63. Bob's Cave under Mumbles Head, a large sea cave scoured by sand. (Margaret Hodge)
Barry Stewart for Figures
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