Physiological response to irradiance, temperature and co-cultivation in Antarctic engineering brown algae (Desmarestia menziesii and D. anceps)

The Western Antarctic Peninsula (WAP) is a hot spot of global warming, including decreased sea-ice cover during winter and increased sedimentation during summer due to glacial melt. Subsequently, an altered irradiance and temperature regime in the water column may affect the performance of primary producers and change competitive structures. The brown, subtidal macroalgae Desmarestia menziesii and D. anceps are ecosystem engineers and of extreme importance for the Antarctic coastal ecosystem. Individuals of both species were collected from the field during the austral summer and exposed in two experiments to different temperatures (2 and 7 degrees C) or different irradiances (high and low) in combination with co-culturing the two algal species together (two-factorial design). No temperature, irradiance or co-cultivation effects on growth rates of D. menziesii and D. anceps were detected, but effects were possibly masked by the very low growth rates. Both D. menziesii and D. anceps are season anticipators, showing highest growth in late winter/spring and a dormancy state during summer. Photosynthetic efficiency was usually higher at 2 degrees C and low irradiance conditions compared to 7 degrees C and high irradiance and no co-culturing effects were detected. Parameters derived from P-E curves (rETR(max), E-k and alpha) were higher in D. menziesii compared to D. anceps, reflecting zonation patterns in the field. Future multifactorial experiments, taking seasons and different life-stages into account, are particularly needed to elucidate year-round effects of global warming on macroalgal key species that form the energetic base of the Antarctic coastal food webs.