Stress physiology and reproductive phenology of Arctic endemic kelp Laminaria solidungula J. Agardh

Abstract

The reproductive phenology and the responses of the early life history stages of the Arctic endemic kelp Laminaria solidungula to global climate change stressors were investigated. This species inhabits low-light areas at depths up to 18 m and under the canopy of other large kelps in shallower depths. Around Svalbard, fertile sporophytes had been collected in late spring to early autumn. This observation suggests that sporogenesis starts in late autumn, continuing throughout the winter and ending in early spring, or that reproduction may occur throughout the year, especially among deepwater population where diel fluctuating low light may be perceived as short days to induce sporogenesis. Fertile sporophytes were induced to release spores that were subsequently exposed to different temperatures (2, 7, 12, 17 °C) in isolation and in interaction with ultraviolet radiation (UVR). Results showed a high temperature affinity up to 12 °C for meiospore germination and growth, but its photosynthesis was low-light-adapted and susceptible to UVR. After 16 days of cultivation, germlings died under 17 °C and gametophyte size was largest at 12 °C. After 48-day cultivation under continuous daylight, gametogenesis was not observed. The projected ocean warming will unlikely negatively affect photosynthesis and growth of micro- and macrostages of L. solidungula. Conversely, the susceptibility of meiospores and gametophytes to high PAR and UVR can disrupt the completion of the life cycle. However, sporogenesis and gametogenesis, which are the key processes for the survival of this Arctic endemic species that requires low temperature and short days, can still occur in deepwater habitats.