Diurnal carbon dioxide exchange rates of Saccharina latissima and Laminaria digitata as affected by salinity levels in Norwegian fjords

Abstract

The Norwegian fjords are strongly influenced by freshwater runoff from the mountain regions as a result of high precipitation. The macroalgae growing in the fjords may therefore be frequently exposed to low salinity levels. This may affect the potential for cultivating kelp in the fjords. In the present study, the sensitivity to salinity levels of 10, 16, 24 or 34‰ was studied by measuring the carbon dioxide exchange rate (CER) in young sporophytes of Saccharina latissima and Laminaria digitata continuously over several days. A positive CER was found down to the freezing point of −2 °C as well as a positive CER during darkness depending on the irradiance level of the previous day. Decreasing the salinity from 34 to 24, 16 or 10‰ reduced the daily CO2 uptake by 50, 85 or 100%, respectively, in S. latissima. The negative effect of decreasing salinity to 10‰ was irreversible. In L. digitata, the daily CO2 uptake was reduced by 20, 30 or 40% by decreasing the salinity from 34‰ to the respective salinity levels. The reduction in the CER at 10‰ was fully reversible. These results were consistent with the observations in a fjord dominated by brackish water where L. digitata was abundant and S. latissima absent.