The natural history of the Hardangerfjord

Abstract

Data on phytoplankton and hydrography from the 1955–56 survey of the Hardangerfjord area, western Norway, have been used for tracing environmental influences upon horizontal and vertical distribution in the phytoplankton from offshore waters to the innermost fjord branch. Examples are given of effects of temperature, salinity, and submarine light upon distribution in coccolithophorids, diatoms, and dinoflagellates. A more unusual effect of the hydrographic differences between the outer coastal waters and the fjord waters was recorded in the overall horizontal distribution of diatoms. Relative poverty in number of species of the diatom society in the fjord compared with the outer waters on a yearly basis had no counterpart in the dinoflagellate society. The low level of turbulent activity in the sheltered fjord compared with the outer waters is suggested to place the non-motile pelagic diatoms at a disadvantage with regard to maintenance of pelagic populations in the fjord. Skeletonema costatum, however, did not seem to be adversely affected. A discussion of presumably advantageous properties of this species is concluded with a suggestion that special flotation properties may give the clue to its exceptional position.