The Laminariaceae off North Shapinsay: Changes from 1947 to 1953

Abstract

Four sublittoral surveys, off the north coast of the island of Shapinsay, Orkney, have been completed in May 1947, July 1951, July 1952, and July 1953. The calculated quantity of seaweed from 1 to 6 fathoms was 34,000 tons during the initial survey of May 1947 after a comparatively mild winter and before the period when bad weather brings about the loss of large quantities of the previous year's growth of laminaria fronds. The three resurveys were completed after this. The quantity of seaweed in July 1951 was 10,000 tons, and in July 1952 a further reduction was found, bringing down the quantity to 6,000 tons. In July 1953 the quantity had partially recovered, reaching 7,000 tons. The increase was reflected more in the seaweed cover than in density. Between 1952 and 1953 the weight of individual plants had decreased but the number of plants per unit area was greater, which, combined with an increase in the area of seabed covered, made an overall gain in quantity. Laminaria saccharina maintained its dominance in this area throughout the period 1947–53.