The aim of this thesis is to give insight into how a short term exposure to higher water temperatures affect photosynthesis in two of the most important species of the Norwegian kelp forest; Laminaria digitata and Saccharina latissima. In addition the effect of increased water temperature on kelp growing in the temperate regions, Trondheimsfjorden, will be compared the effect on kelp growing in the arctic region, Svalbard.