The natural history of the Hardangerfjord 7. Horizontal distribution of the fauna of rocky shores

Abstract

As part of a joint survey of the natural history of Hardangerfjorden, western Norway, a study of the fauna of rocky shores was made; this was carried out in the years 1955–63. In the mountains around the inner parts of the 180 km long fjord there are glaciers and numerous fields of eternal snow. Melting of snow and ice in spring and summer causes a lowering of the salinity in the surface layers of the fjord. In summer there is a gradient from euhaline conditions in the outer part to mesohaline waters in the inner parts. Detailed records of distribution and notes on ecology are given for all the species together with maps of distribution for selected species. The fauna changes in composition from the outer to the inner reaches of the fjord, and the fjord was therefore divided into four areas, an outer, an intermediate, and an inner fjord area, and the fjord branches, each characterized by the presence or absence of certain species. The features marking the change in fauna were 1) a decrease in the total number of species from the outer area to the fjord branches, and 2) dominance of boreal and southern or lusitanian-boreal species in the outer area and dominance of boreal and northern or arctic-boreal species in the fjord branches. The effects of certain environmental factors upon specific distribution are discussed. Exposure, low salinity in the surface layers in summer, and sea and air temperature ranges appear to be the main factors responsible for the changes in the fauna along the fjord.