Description: In natural environments, marine biotas are exposed to a variety of simultaneously acting abiotic factors. Hereof, temperature, irradiance and CO2 availability are major factors influencing the physiological performance of marine macroalgae. In order to test whether elevated levels of CO2 may remediate the otherwise reduced performance of uncalcified seaweeds under other stressful abiotic factors, we performed multi-factorial experiments with the red alga Chondrus crispus rom Helgoland (North Sea) with two levels of CO2, temperature and irradiance, respectively: Low and high pCO2 levels were tested in combination with either (1) optimal and low irradiances or (2) optimal and sub-lethal high temperatures for growth. Performance of C. 33 crispus was evaluated as biomass increase and relative growth rates (RGR), gross photosynthesis, and pigment content. Acclimation of growth and photosynthesis was measured after 4 and 8 days. Acclimation time was crucial for elucidating single or combined CO2 effects on growth and photosynthesis. Significant CO2 effects became evident only in combination with either elevated temperature or reduced irradiance. Growth and photosynthesis showed divergent pattern: the RGR and biomass significantly increased only under a combination of high pCO2 and elevated temperature; gross photosynthesis was significantly reduced under high pCO2 conditions at low irradiance. Pigment content varied in response to irradiance and temperature,respectively, but was independent of pCO2.

Description: Macroalgae in Kongsfjorden were surveyed by divers down to 30 m depth at Hansneset, Blomstrand (78° 39’N, 11°57’E). In total, 62 species were identified, 16 Chlorophyta, 25 Phaeophyceae and 21 Rhodophyta. The majority of species (53.5%) belonged to the Arctic cold-temperate group, followed by species distributed from the Arctic to the warm-temperate region (25.9%). Four endemic Arctic species (Laminaria solidungula, Acrosiphonia flagellata, A. incurva, Urospora elongata) were found. Two species (Lithosiphon filiformis, Mikrosyphar polysiphoniae) were new for Svalbard. Chlorophyta, Phaeophyceae and Rhodophyta extended from the eulittoral zone down to 11, 21 and 〉30 m depths, with maximum biomasses at 1- 5 m, 5- 10 m and 5- 30 m depth, respectively. Annual and pseudoperennial species had highest biomasses in the upper 5 m, while perennials were distributed deeper. The highest biomass (8600 g m-2) at 5 m depth included mainly Laminaria digitata, Saccorhiza dermatodea, Alaria esculenta and Saccharina latissima. The biogeographic composition of macroalgae at Hansneset was relatively similar to that of Northeast Greenland, but different from that of Northern Norway, which is characterised by a higher proportion of temperate species. Climate warming and ship traffic may extend some of the distribution ranges of macroalgae from mainland Norway to Svalbard.

Description: We did a survey on macroalgal diversity along a transect off Hansneset (78°39′N, 11°57′E), Kongsfjorden, western Svalbard, between 0- and 〉 15-m depths in 2012/2013. One major intention was to compare our data to a similar study performed in 1996/1998 at the same site and to document possible changes. We identified 58 species of macroalgae, 12 Chlorophyta, 31 Phaeophyceae, and 15 Rhodophyta. One species (Sphacelorbus nanus) is a new record for Svalbard. Fourteen species are new records for the Kongsfjorden area. Fertile tetrasporophytes of Turnerella pennyi (Cruoria phase) and the microscopic Chlorochytrium stage of Spongomorpha aeruginosa are also recorded for the first time from Svalbard. An increase from 20 to 45 species in the littoral in 2012/2013 compared with 1996/1998 was recorded. This study increases the total macroalgal species diversity of Kongsfjorden to 76. While 62 species were found in 1996/1998 and 58 in 2012/2013, only 42 were common to both investigations. We have made some taxonomic annotations to 20 species/ genera. Strikingly, we did not find again some red algae, such as Hildenbrandia rubra, Palmaria palmata, Polysiphonia spp., or Scagelia pylaisaei, that had been recorded in 1996/1998. Possible reasons for the changes based on recent knowledge from Kongsfjorden are discussed.