Thanet Coast in the extreme south-east of England has been selected on account of the unusual communities that are found on this, the longest continuous stretch of coastal chalk in the UK. It represents approximately 20% of the UK resource of this type and 12% of the EU resource. This site contains an example of reefs on soft chalk along the shore. Thanet has sublittoral chalk platforms that extend into the littoral and form chalk cliffs. The sublittoral chalk reefs within the site are comparatively impoverished, owing to the harsh environmental conditions in the extreme southern area of the North Sea, but they are an unusual feature because of the scarcity of hard substrates in the area. Infralittoral kelp forests are characteristically absent, owing to the high turbidity of the water. The subtidal chalk platforms extend offshore in a series of steps dissected by gullies. Species present include an unusually rich littoral algal flora, essentially of chalk-boring algae, which may extend above high water mark into the splash zone in wave-exposed areas. Thanet remains the sole known location for some algal species.
Thanet Coast provides the second most extensive representation of chalk caves in the UK on the extreme south-east coast of England. The site is bordered by about 23 km of chalk cliffs with many caves and stack and arch formations. Partially submerged caves around Thanet vary considerably in depth, height and aspect and hence in the algal communities present. Some caves extend for up to 30 m into the cliffs and reach 6-10 m in height, although many are much smaller. They support very specialised algal and lichen communities containing species such as Pseudendoclonium submarinum and Lyngbya spp., some of which were first described from Thanet and have never been recorded elsewhere.