THE EFFECTS OF LIGHT AND NITROGEN ON GROWTH, PIGMENT CONTENT, AND BIOCHEMICAL COMPOSITION OF GRACILARIA FOLIIFERA V. ANGUSTISSIMA (GIGARTINALES, RHODOPHYTA)1

Abstract

ABSTRACTThe combined effects of light intensity and nitrogen (NO3−) on growth rate, pigment content, and biochemical composition of Gracilaria foliifera v. angustissima (Harvey) Taylor was investigated using outdoor continuous cultures.Growth of Gracilaria increased linearly with increasing light to 0.43 doublings d−1 at high light levels (383 ly d−1 of in situ light), suggesting that light may often limit growth of this plant in nature. Chlorophyll a and phycoerythrin contents were inversely proportional to light level and growth rate. However, pigment content did not affect the growth capacity of Gracilaria. There was no increase in growth or pigment content with increasing additions of nitrogen. The low nitrogen treatment was unenriched seawater that had higher NO3− levels than most coastal waters (influent = 8.61 μM; residual = 0.94 μM). When growing near its maximum rate under high light intensities, Gracilaria had a significantly (P < 0.001) lower phycoerythrin: chlorophyll a ratio (phyco: Chl a) than did Gracilaria growing more slowly under lower light (Phyco:Chl a of 2.8 ± 0.2 vs. 3.8 ± 0.3). Faster growing plants also had C:N ratios above 10, indicating N‐ limitation. In addition to harvesting light the phycobiliproteins of Gracilaria may store nitrogen.Growth rates of Gracilaria correlated negatively with ash (r =–0.85) and positively with the carbon: phycoerythrin ratio (r = 0.85), suggesting that these two indices can be used to estimate growth in the field.