TITLE	The effect of ulvoid macroalgae on the inorganic carbon utilization by an intertidal seagrass Thalassia hemprichii
AUTHOR	Shao-Lun LIU Department of Biology, National Changhua University of Education, Changhua 500, Taiwan Wei-Lung WANG Department of Biology, National Changhua University of Education, Changhua 500, Taiwan Danilo T. DY Marine Biology Section, Department of Biology, University of San Carlos, Cebu City 6000, Philippines Cheng-Chang FU Oldinburgh Company, Ltd., Taipei 100, Taiwan
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ABSTRACT	Blooms of ulvoid macroalgae (mainly Enteromorpha and Ulva) have covered 80% of the intertidal seagrass bed at Wanlitung, southern Taiwan, effectively shading the seagrasss species Thalassia hemprichii resulting in a decrease in photosynthetic performance and low inorganic carbon (Ci) uptake. We looked for evidence of Ci limitation and investigated the Ci utilization characteristics of ulvoid-free and ulvoid-covered T. hemprichii. The rapid light curve (RLC) function of the Diving-PAM (Diving-PAM, Walz, Germany) was used to measure in situ photosynthetic performance (based on the effective quantum yield of PSII [Y] values) of intact seagrasses that were placed in small incubating chambers. Significantly, a lower RETRmax (maximum relative electron transport rate) and Ek (light intensity at the onset of saturation) were noted in the ulvoid-covered compared to the ulvoid-free T. hemprichii, suggesting that the former has acclimatized to the low light environment becoming a "shade type" plant. The ulvoid-covered T. hemprichii showed some evidence of Ci limitation since a significant increase in RETRmax (up to 46%; P < 0.05) was noted after an increase in the concentration of NaHCO3 from 2.2 (normal seawater) to 6.2 mM. In terms of Ci utilization characteristics, T. hemprichii could directly absorb HCO3- as the major Ci source but partially depended on the extracellular carbonic anhydrase (CA) to convert HCO3- to CO2 prior to uptake in the ulvoid-free, high light-adapted populations. A wastewater stream with a high nutrient load coming from the urbanized area may have caused the frequent blooms of ulvoid macroalgae.
KEYWORD	Bicarbonate; Photosynthesis; Taiwan; Ulvoid bloom;
ARTICLE INFO	Botanical Bulletin of Academia Sinica, Volume 46 Number 3 July 2005, page 197-203, 7 pages
PUBLISHER	Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan, Republic of China