Inherent tolerance of extreme seasonal variability in light and salinity in an Arctic endemic kelp (Laminaria solidungula)

Abstract

The kelp Laminaria solidungula is an important foundation species in the circumpolar Arctic. One of the largest populations of L. solidungula in the Beaufort Sea occurs in Stefansson Sound, off the north coast of Alaska. We surveyed kelp populations in the Stefansson Sound Boulder Patch and found that inshore sites in close proximity (3.5 km) to river input and increased turbidity exhibited lower sporophyte densities (0.36 ± 0.44 · m^-2 ) than more offshore sites (>7 km) to the west (0.72 ± 0.48 · m^-2 ) and east (4.72 ± 1.51 · m^-2 ). We performed culture experiments to examine the possible combined effects of salinity and light on microscopic sporophyte production. Gametophytes cultured in the low salinity treatment (10) were unable to produce sporophytes regardless of light level. The highest light level tested (40 µmol photons · m^-2 · s^-1 ) produced the greatest sporophyte densities (0.037 ± 0.08 · mm^-2 ) at a salinity of 30. Subsequent experimental work on the effect of salinity on microscopic stages revealed that haploid stages were not capable of producing sporophytes at a salinity of 10, but 3-month-old microscopic sporophytes were able to persist in the lower (10 and 20) salinity treatments. Although L. solidungula sporophytes have apparently acclimated to extreme salinity (<5-33) and light variations, the vulnerability of haploid microscopic stages to reduced salinity has the potential to affect future populations as the timing and magnitude of freshwater input to the Arctic Ocean changes.

Keywords: Arctic; acclimation; freshwater input; kelp; polar; recruitment; salinity; sexual reproduction.