Thalli of Corallina officinalis Linnaeus were harvested at 1-h intervals during low tide in Barrancas Blancas (Patagonia, Argentina) on clear days to examine diurnal changes of the UV-absorbing mycosporine-like amino acids (MAAs) shinorine and palythine. Corallina officinalis is found in two growth forms in the mid and the lower intertidal zone, which were collected and analyzed separately. Recovery was measured in algal samples kept in large open containers and sampled every hour overnight. The samples were dried and the amount of MAAs analyzed by means of high performance liquid chromatography (HPLC). The average MAA concentration was 0.17 mg/g (range: 0.04 – 0.34) dry weight (DW) for shinorine and about 1.24 mg/g (0.11 – 5.2) DW for palythine in samples from the low intertidal zone and about 0.18 mg/g DW for shinorine (0.05 – 0.58) and 1.89 mg/g (0.2 – 5.76) DW for palythine in the mid intertidal algae. In the low intertidal strain the concentration of palythine, and not so pronounced for shinorine, significantly increases during the morning and shows a sudden decrease in the afternoon at around 15:00 h. Samples were taken on different days at the same time but had a different preirradiation (due to the rhythm of the tide). In most cases an increase of palythine upon longer preexposure to solar radiation was visible. In contrast, no correlation was found between MAAs and radiation dose. Corallina thalli growing in the mid intertidal zone did not show such pronounced daily changes in MAA composition but higher concentrations of shinorine and palythine at the same local time upon longer preexposure to solar radiation.
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