Acclimation of brown algal photosynthesis to ultraviolet radiation in Arctic coastal waters (Spitsbergen, Norway)

In field studies conducted at the Kongsfjord (Spitsbergen) changes of the i rradiance in the atmosphere and the sublittoral zone were monitored from th e beginning of June until the end of August 1997, to register the minimum a nd maximum fluxes of ultraviolet and photosynthetically active radiation an d to characterise the underwater light climate. Measurements of photosynthe sis in three abundant brown algal species (Alaria esculenta, Laminaria sacc harina, Saccorhiza dermatodea) were conducted to test whether their photosy nthetic performance reflects changing light climate in accordance with dept h. Plants sampled at various depths were exposed to controlled fluence rate s of photosynthetically active radiation (400-700 nm), W-A (320-400 nm) and UV-B (280-320 nm). Changes in photosynthetic performance during the treatm ents were monitored by measuring variable chlorophyll fluorescence of photo system II. In each species, the degree of inhibition of photosynthesis was related to the original collection depth, i.e. shallow-water isolates were more resistant than plants from deeper waters. The results show that macroa lgae acclimate effectively to increasing irradiance levels for both photosy nthetically active and ultraviolet radiation. However, the kinetics of accl imation are different within the different species. It is shown that one im portant strategy to cope with higher irradiance levels in shallow waters is the capability for a faster recovery from high light stress compared to is olates from deeper waters.