Tank cultivation of the red alga Palmaria palmata: Effects of intermittent light on growth rate, yield and growth kinetics

Tank cultivation of marine macroalgaeinvolves air-agitation of the algal biomassand intermittent light conditions,i.e.periodic, short light exposure of thethalli in the range of 10 s at the watersurface followed by plunging to low lightor darkness at the tank bottom andrecirculation back to the surface in therange of 1–2 min. Open questions relate toeffects of surface irradiance on growthrate and yield in such tumble cultures andthe possibility of chronic photoinhibitionin full sunlight. A specially constructedshallow-depth tank combined with a darktank allowed fast circulation times ofapproximately 5 s, at a density of 4.2 kgfresh weight (FW) m^-2s^-1. Growthrate and yield of the red alga Palmaria palmata increased over a widerange of irradiances, with no signs ofchronic photoinhibition, up to agrowth-saturating irradiance ofapproximately 1600 mol m^-2s^-1 in yellowish light supplied by asodium high pressure lamp at 16 h light perday. Maximum growth rate ranged at 12% FWd^-1, and maximum yield at 609 gFW m^-2 d^-1. This shows that highgrowth rates of individual thalli may bereached in a dense tumble culture, if highsurface irradiances and short circulationtimes are supplied. Another aspect ofintermittent light relates to possiblechanges of basic growth kinetics, ascompared to continuous light. For thispurpose on-line measurements of growth ratewere performed with a daily light reductionby 50% in light-dark cycles of 1, 2 or 3min duration during the daily light period.Growth rates at 10 °C and 50 molphoton m^-2 s^-1 dropped in allthree intermittent light regimes duringboth the main light and dark periods andreached with all three periodicitiesapproximately 50% of the control , with noapparent changes in basic growth kinetics,as compared to continuous light.