The high Arctic Kongsfjorden (Spitsbergen, Norway) implies extreme conditions for sea-weeds. Strong seasonality leaves only a few summer month for photosynthetic activity and growth. Thus, seaweed primary production as key process in the polar marine carbon cycle needs to be very effective. However, there is a lack of information on the photosynthetic per-formance and light requirements in the polar Svalbard archipelago region and the Arctic in general. Estimates on the primary production of macroalgae do not even exist. Nevertheless, such data are essential for the quantification oft the local marine carbon cycle and understand-ing the functional relationships of the marine food web or estimating potential effects of cli-mate change on marine primary production. This thesis aims at supplying parts of the missing basis data as a contribution to the long term research project “Biology of Arctic benthic algae“ of the Alfred-Wegener-Institute, Helmholtz-Centre for Polar- and Marine Research. In this respect between July and August 2013 four brown and three red algae species were collected along a sublittoral depth transect in depths of 2.5 to 20 m off Hansneset in Kongs-fjorden in order to determine their photosynthetic performance in a light gradient. Pulse Am-plitude Modulation (PAM) fluorometry and measurements of oxygen gas exchange via fibre optical sensors resulted in relative electron transport rates and oxygen production rates, re-spectively. Those formed the basis for generating light response curves fitted in use of the model by JASSBY & PLATT (1976). The model suited the data but not as good as expected since in reality there seem to exist two (or more) overlapping response curves, one for the illuminated front and one for the shaded back of the samples. Nevertheless, the used model displays an acceptable compromise of the overlapping curves. Therefore, the resulting photo-synthesis parameters maximum net oxygen production Pmax, photosynthetic efficiency Alpha and photosynthetic light saturation point Ik may be used for future productivity estimates. PAM fluorometry in the phylloid gradient of the kelps Alaria esculenta, Laminaria digitata and Saccharina latissima revealed significantly higher values for the photosynthesis parame-ters maximum relative electron transport rate (rETRmax), Alpha and Ik in 20 cm distance to phylloid base compared to 40 cm and 60 cm distance while values of 40 cm and 60 cm dis-tance resemble each other. Thus, representative sampling of the investigated kelp species should not be conducted in the vicinity of the basal meristematic zone. Moreover, species show significant differences between each other only at 40 cm and 60 cm distance to the phylloid base. All in all photosynthesis measurements in the depth gradient did not reveal any clear pattern of their variability. The results of PAM fluorometry and optical fibre measurements show consistency in most cases, but there are also clear exceptions, e. g. with regard to the resulting clear trends of brown algae photosynthesis parameters in PAM fluorometry contrary to com-pletely missing trends in optical fibre measurements. The photosynthetic efficiency Alpha shows almost no significant difference with depth for all investigated species, which could mean that all species are acclimated almost perfectly to the light conditions of their natural habitats. Hence, the study gives insight into the acclimation potential of the investigated species to-wards prevailing light conditions along the depth gradient. Moreover, it provides the basis for first primary production estimates of the Arctic kelp ecosystem of Kongsfjorden through cor-relation with in situ biomass and irradiance data.