Salinity and irradiance effects on growth and maximum photosynthetic quantum yield in subarctic Saccharina latissima (Laminariales, Laminariaceae)

Abstract

In subarctic regions, melting of glaciers creates stressful environmental conditions, such as reduced salinity and irradiance, in coastal benthic habitats such as kelp beds. Our goal was to determine whether these stressors differently affect kelp juveniles of Saccharina latissima originating from two environmentally distinct shores; one under oceanic and one under estuarine glacial influence. Laboratory tests assessed the effects of varying salinities and irradiances on growth and maximum quantum yield (Fv/Fm) of photosystem II of S. latissima. Overall, growth rates decreased with decreased salinity and irradiance. Growth rates of juveniles from the glacially influenced shore were significantly lower than those of the oceanic shore in most salinity and irradiances treatments. Juveniles from both shores grew negligibly at salinities below 13 and an irradiance of 5 μmol photons m-2 s-1. At salinity 10, Fv/Fm was significantly reduced but Fv/Fm was not affected by decreased irradiance. S. latissima proved to be relatively tolerant to reduced salinities and irradiances but we detected limits to its resilience. Our results suggest that S. latissima populations exhibit phenotypic plasticity in their growth responses. This plasticity appears to be constrained within specific seasonal growth patterns in accordance with their environment of origin.