Influence Of Ultraviolet Radiation On The Pigmentation And Growth Of The Red Alga, Gracilaria Salicornia

Abstract

Physiological damage to macroalgae from both UVA (320-400 nm) and UVB (280-320 nm) radiation is well documented in the scientific literature. Due to the occurrence of mycosporine-like amino acids (MAAs) in marine algae from the poles to the tropics, and their UV absorption maxima between 310 and 360 nm, it is assumed that MAAs act as sunscreens to counter this stress while allowing the light-harvesting pigments to absorb the maximum photosynthetically active radiation (PAR, 400-700 nm) for growth. This study agrees with previous investigations that MAA concentration is positively correlated with natural doses of UV radiation. In addition, this study addresses the metabolic cost of producing these photoprotective compounds. Specifically, does this metabolic cost impact growth rate? Gracilaria salicornia was grown in both UV transparent (full sunlight) and UV filtered (50% reduced irradiance below 350 nm) 40-liter tanks, and growth rate and intracellular concentrations of photosynthetic pigments were compared during two time-series experiments (14 and 21 days) between June and August, 2003. Of the five MAAs consistently detected, porphra-334 (λmax=334) showed the quickest and most substantial divergence in concentration between the two treatments (full sunlight = higher concentration). Shinorine (λmax=334) and palythene (λmax=320) responses generally lagged by two to three days and were less pronounced. The concentration of palythene (λmax=360) and mycosporine-glycine (λmax=309) also diverged, but differences were very small for most days in each time-series. Pigment responses also diverged midway through the experiment, with carotenoid concentration in the control treatment increasing relative to the experimental treatment. Growth rates between the two treatments were not statistically different.