Interactive effects of nutrient availability, temperature, and irradiance on photosynthetic pigments and color of the brown alga Undaria pinnatifida

Abstract

Color is one of the important factors that determine the commercial value of cultivated marine macroalgae such as the brown alga Undaria pinnatifida (Laminariales; Phaeophyta) in Japan. Macroalgal color is fundamentally derived from the algal photosynthetic pigment content, which is affected by abiotic factors. However, little is known about the quantitative relationship between pigment content and color and the direct effects of abiotic factors on the color of marine macroalgae. We conducted a 24-day indoor culture experiment to assess the combined effects of nutrient availability (enriched and nonenriched seawater), seawater temperature (15 and 5 °C), and irradiance (180 and 30 μmol photons m−2 s−1) on the concentrations of six pigments (chlorophyll (Chl) a, Chl c 1, Chl c 2, fucoxanthin, violaxanthin, and zeaxanthin) and three color values (lightness L*, redness a*, and yellowness b*) of U. pinnatifida sporophytes. Negative correlations between pigment content and color values of the cultured algae were detected. Reduced nutrient availability, decrease in temperature, and elevated irradiance resulted in decreased pigment contents and increased color values. Moreover, a significant interaction between nutrient availability and temperature indicated that the positive effect of nutrient enrichment was antagonized by a decrease in temperature. These results suggest that U. pinnatifida can discolor under nutrient-poor, winter temperature, and saturated irradiance conditions. To increase the commercial value of this species, artificial nutrient enrichment during spring or cultivation from a deeper depth may be effective.