Glacial and depth influence on sublittoral macroalgal standing stock in a high-Arctic fjord

The motivation behind this study is the progression of global warming, which severely affects the entire Arctic and could have effects on macroalgal assemblages. Three sampling sites were located at different distances to glacier fronts to study the effect of glacial exposure on macroalgal community composition and standing stock. In addition, the variability between two depths (5 and 10 m) was investigated. The subtidal communities at each site and depth were dominated by brown macroalgae of the order Laminariales, which made up over 95% of the macroalgal biomass and at least 65% of the macroalgal abundance at each site. The mean macroalgal species richness and abundance were reduced at glacially impacted sites, but the differences were not statistically significant. The community structure based on abundance data varied between the clear and glacially exposed sites due to the higher abundances of Laminaria digitata, Phycodrys rubens and Alaria esculenta at the clear site and Saccharina latissima at the glacial sites. The biomass structure did not vary between sites. The kelp biomass distribution between depths was patchy and dependent on water properties. The maximum biomass was observed at the depth of 10 m at the clear site, while it was observed at shallower depths at the glacial sites. As deglaciation proceeds, new seabed areas are uncovered, and the number of ice-free days grows, creating favourable conditions for macroalgal expansion. However, due to increased turbidity close to the glacier fronts, decreases in species richness, abundance and biomass of macroalgae are likely to occur, as well as the reorganization of the community structure. Such changes may intensify with continued Arctic warming. The hypothesis about reduction of macrophyte abundance and biomass due to the glacial impact was not supported by our data.