Kan rødalgen Gracilaria vermiculophyllas invasivitet tilskrives en høj vækstrate i kombination med evnen til at dække næringsstofbehovet ved lave næringsstofkoncentrationer? Can the invasiveness of the red alga Gracilaria vermiculophylla be caused by a high growth rate in combination with the ability to cover its requirements for nutrients at low nutrient concentrations?

Kathrine Lørup Johnsen

Studenteropgave: Semesterprojekt


The invasive red alga Gracilaria vermiculophylla has its origins in Asia, but in recent years it has spread across the USA and Northern Europe, including Denmark, where it was first registered in 2003. Few years after its introduction it has become the dominant species in several areas. The aim of this project was to investigate the hypothesis that the success of G. vermiculophylla as an invasive species can be attributed to a combination of r- and K-strategic traits giving the alga a competitive advantage over native species. G. vermiculophylla has relatively high growth rates, which is typical for r-strategists. In the project it was investigated whether in addition G. vermiculophylla is efficient in taking up nutrients (nitrate, ammonium and phosphate) relative to its requirements, which is typical for K-strategists. In a series of experiments uptake rates were measured as a function of substrate concentrations of the three nutrients, and the data were combined with unpublished data from previous experiments, in which growth rates were measured as a function of nitrogen and phosphorus content in the algal tissue. On the basis of the two sets of data, the growth rate of G. vermiculophylla was determined as a function of external nutrient concentrations, and the results were compared to similar data for a number of native species of algae. In conclusion it was found that G. vermiculophylla needs relatively high ambient concentrations of all three nutrients, but of nitrate in particular, when this is the only source of nitrogen, to sustain maximum growth. Hence there is no indication that G. vermiculophylla is particularly efficient in taking up nutrients, and hence the results of this project do not support a confirmation of the hypothesis.

UddannelserMiljøbiologi, (Bachelor/kandidatuddannelse) Bachelor el. kandidat
Udgivelsesdato21 jan. 2014
VejledereMorten Foldager Pedersen


  • Gracilaria vermiculophylla