Introduction

Abstract

Abstract From Shetland to Scilly, the British Isles extend through 11 degrees of latitude, a distance of about 1250 km. Between eastern England and western Ireland they range through 13 degrees of longitude, about 900 km. The northern and western boundaries of this region face the open Atlantic; oceanic influences, locally modified by geographical and topographical factors, largely modulate the character of the marine environment. The eastern side of the British Isles bounds a shallow epicontinental sea; oceanic influences in the North Sea decrease towards the south, where the proximity of the European landmass has a different modifying effect. In the south, the complex hydrography of the Channel results in rapidly changing physical characteristics along its length, again with discernible environmental consequences. The Irish Sea, and major embayments such as the Bristol Channel, Liverpool Bay, the Scottish firths, and the Wash, are also characterized by particular physical conditions and, if geography is stretched to include the Channel Isles, the Gulf of St. Malo exemplifies further modifications of the marine environment. The effects of major physical factors are everywhere mediated by local geographical and topographical influences. Thus, throughout the region there exist marked gradients in the marine environment which are reflected in profuse variation in the characteristics of different marine habitats, with consequent effects on the nature of the marine fauna. Good illustrations of this have been provided by Holme (1961, 1966) and Cabioch (1968) in their studies of the environmental characteristics, bottom deposits, and benthic fauna of the Channel.