The Raising of Intertidal Algal Zones on Fair Isle

Abstract

Fair Isle lies (59? 35' N.-44? W.) off the north coast of Scotland, 20 miles south of the southern tip of Shetland and approximately half-way between Shetland and Orkney. During the course of a preliminary survey of the marine algae on the coast of Fair Isle at the end of June 1952, it became obvious to the authors that the algal vegetation of the island differed in many respects from that found on other parts of the British coast with which they were familiar. The position of the algal zones in relation to tide levels particularly showed features of interest when considered in relation to the sea and atmospheric conditions of the island. The stormy sea conditions and the prevalence of low cloud and fog during the summer months of the year (see Fig. 1) seemed to be of great importance in influencing the occurrence of algal vegetation on the shore. In such an open-sea position, swift tidal currents, meeting the steep cliffs which compose the greater part of the coastline of Fair Isle, produce surf even on the calmest day. On the steepest cliffs only a limited algal vegetation is found, owing, no doubt, to the considerable battering by enormous waves during gales. The authors were unable to make a close inspection of such cliffs, because, although the weather was fairly calm during the period of the survey, there was no day when it was sufficiently calm to use a small boat. In places where the cliffs inclined from the vertical and resolved into series of sloping walls and rock ledges, an algal vegetation was found in which zones, normally intertidal in position, extended far above high-water mark. In illustration of this a survey was made (as detailed as possible under the very difficult working conditions) of a steep exposed area of shore at North Gavel, Bu Ness (Fig. 2, point B). For comparison with it a second survey was made on the north side of the sheltered bay of North Haven (Fig. 2, point A). The method of survey was the same in both areas and was based on a transect line. A chain was thrown through the intertidal region along the chosen line and vertical and horizontal distances were worked out by means of 2 m. rules. Any more accurate method was precluded by the severe working conditions. General views of the North Gavel area are shown in P1. 15. In recording the presence of plants on the transect lines, the rock