Responses of three tropical seagrass species to CO2 enrichment

• Published in: Marine biology Vol. 162; no. 5; pp. 1005 - 1017
• Main Authors: Ow, Y. X., Collier, C. J., Uthicke, S.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.05.2015; Springer Nature B.V
• Subjects: Acidification; Algae; Biomass; Biomedical and Life Sciences; Carbon dioxide; Chemical analysis; Coastal ecosystems; Ecological function; Freshwater & Marine Ecology; Greenhouse gases; Life Sciences; Marine & Freshwater Sciences; Marine biology; Marine ecology; Microbiology; Ocean acidification; Oceanography; Original Paper; Photosynthesis; Physiological responses; Productivity; Seawater; Water analysis; Zoology; Specific Leaf Area; Photosynthetically Active Radiation; Dissolve Inorganic Carbon; Photosynthetic Rate; Ocean Acidification
• ISSN: 0025-3162; 1432-1793
• DOI: 10.1007/s00227-015-2644-6

Increased atmospheric carbon dioxide leads to ocean acidification and carbon dioxide (CO 2 ) enrichment of seawater. Given the important ecological functions of seagrass meadows, understanding their responses to CO 2 will be critical for the management of coastal ecosystems. This study examined the physiological responses of three tropical seagrasses to a range of seawater pCO 2 levels in a laboratory. Cymodocea serrulata , Halodule uninervis and Thalassia hemprichii were exposed to four different pCO 2 treatments (442–1204 μatm) for 2 weeks, approximating the range of end-of-century emission scenarios. Photosynthetic responses were quantified using optode-based oxygen flux measurements. Across all three species, net productivity and energetic surplus ( P G : R ) significantly increased with a rise in pCO 2 (linear models, P  < 0.05). Photosynthesis–irradiance curve-derived photosynthetic parameters—maximum photosynthetic rates ( P max ) and efficiency ( α )—also increased as pCO 2 increased (linear models, P  < 0.05). The response for productivity measures was similar across species, i.e. similar slopes in linear models. A decrease in compensation light requirement ( E c ) with increasing pCO 2 was evident in C. serrulata and H. uninervis , but not in T. hemprichii . Despite higher productivity with pCO 2 enrichment, leaf growth rates in C. serrulata did not increase, while those in H. uninervis and T. hemprichii significantly increased with increasing pCO 2 levels. While seagrasses can be carbon-limited and productivity can respond positively to CO 2 enrichment, varying carbon allocation strategies amongst species suggest differential growth response between species. Thus, future increase in seawater CO 2 concentration may lead to an overall increase in seagrass biomass and productivity, as well as community changes in seagrass meadows.