The Bottom Fauna of the English Channel

Extract

A survey has been made of the bottom fauna in ca. 10–50 m along the south coast of England, using a modified anchor-dredge. Particular attention has been paid to the molluscs (both living and dead) and to the echinoderms, only larger or more conspicuous members of other groups being identified.

Within the Channel there are considerable variations in temperature and other hydrographic conditions, and these are discussed in relation to their possible role as limiting factors in distribution. The fauna and bottom deposits of the different areas covered in the survey are briefly described.

Distribution trends are classified as:

(1) Species generally distributed in the Channel. This is the largest group, and includes three species reaching their northern limits in British waters.

(2) Species confined to the western parts of the Channel.

(a) Western species. Four or five species common at Plymouth in the 1920's, but now absent or very rare. Small numbers are found today only off the south Cornish coast, and those which occur in the North Sea are restricted to the north-western areas. Apart from one species, these forms are not at their geographical limits in the English Channel, and their occurrence may be partly related to the presence of ‘western’, but not necessarily Sagitta elegans, water.

(b) Cornubian species. These are near the northern end of their range, and occur quite commonly off the south Cornish coast, becoming progressively less common farther up-Channel. It is suggested that their distribution is related to an intolerance of the lower winter temperatures in the more eastern part of the Channel.