The distribution and morphology of Fucus distichus in an estuarine environment and the effect of selected ions on the uptake of inorganic carbon and nitrate

Abstract

The morphology, distribution, and habitat of dwarf and normal forms of Fucus distichus in Nehalem Bay were examined. The dwarf form lacked the holdfast and sexual structures of the normal form and was more highly branched. Examples of the dwarf form were found growing as outgrowths of fragmented normal forms indicating that both forms are the same species. The normal form occurred attached to rocks near the mouth of the bay in waters of oceanic salinity. The dwarf form occurred as a free-living form in the salt marshes and in waters of lower salinity. These observations suggested that the occurrence of the dwarf form is related to salinity. Nutrient uptake studies with nitrate and carbon demonstrated that both forms have similar responses to changes in salinity. The dwarf form however, was better adaptated to the lower salinities than the normal form. Both forms showed a drop in carbon uptake and a slight rise in nitrate uptake as salinity was decreased, but the dwarf form maintained near maximal carbon uptake rates to a much lower salinity. It was shown that carbon uptake is sensitive to sodium and potassium ions, and nitrate uptake is sensitive to potassium ions. Reducing the sodium ion concentration by changing the medium composition decreased the carbon uptake rate. This rate was reduced further by the addition of potassium ion. The addition of sodium and potassium specific ionophores to the medium also depressed the uptake rate of carbon. Nitrate uptake was relatively unaffected by decreased sodium concentrations, but was drastically reduced by elevated potassium levels. The potassium specific ionophore valinomycin also produced a significant drop in the nitrate uptake rate. These data suggested that chemical potentials for sodium and potassium drive the uptake of carbon and that potassium is involved in the uptake of nitrate in F. distichus.