Ecological growth strategies in the seaweeds gracilaria foliifera rhodophyceae and ulva sp chlorophyceae photosynthesis and antenna composition
Rosenberg, G.; Ramus, J.
Marine Ecology Progress Series 8(3): 233-242
Photosynthesis (O2 evolution) and seasonal fluctuations in antenna pigments were observed in 2 seaweeds which co-occur in the vicinity of Beaufort, North Carolina, USA. G. foliifera (Rhodophyceae) and U. sp. (Chlorophyceae) were grown in outdoor continuous-flow cultures at ambient incident light (Io) and 0.13Io. Pigment contents and accessory pigment: chlorophyll a ratios were higher at 0.13Io than at Io. Total pigment levels were correlated with soluble N in seaweed tissue. During the spring/summer growing season, pigment levels were low and peaks in pigment content followed nutrient pulses in the ambient seawater. Pigment contents in both species were higher in winter. In G. foliifera, the R-phycoerythrin: chl a ratio was highest in fall-winter and lowest in summer. The higher growth rates achieved by Ulva sp. reflected the higher rates of photosynthesis measured in this species. Photosynthesis-light curves showed that Ulva sp. had a higher photosynthetic capacity (Pmax = 430 .mu.mol O2 evolved g dry wt-1 h-1) and initial slope (in shade acclimated plants) than G. foliifera (Pmax = 160 .mu.mol O2 evolved g dry wt-1 h-1). Increased pigment contents in shade plants of both species resulted in enhanced photosynthetic performance at subsaturating light intensities. Apparently, the effect of transient pigment increases in the summer was to increase Pmax temporarily while, in winter, the effect was to limit the decrease in integrated net photosynthesis in the face of decreased light and temperature.