title: CO₂ and inorganic nutrient enrichment affect the performance of a calcifying green alga and its noncalcifying epiphyte.
abstract: Ocean acidification studies in the past decade have greatly improved our knowledge of how calcifying organisms respond to increased surface ocean CO2 levels. It has become evident that, for many organisms, nutrient availability is an important factor that influences their physiological responses and competitive interactions with other species. Therefore, we tested how simulated ocean acidification and eutrophication (nitrate and phosphate enrichment) interact to affect the physiology and ecology of a calcifying chlorophyte macroalga (Halimeda opuntia (L.) J.V. Lamouroux) and its common noncalcifying epiphyte (Dictyota sp.) in a 4-week fully crossed multifactorial experiment. Inorganic nutrient enrichment (+NP) had a strong influence on all responses measured with the exception of net calcification. Elevated CO2 alone significantly decreased electron transport rates of the photosynthetic apparatus and resulted in phosphorus limitation in both species, but had no effect on oxygen production or respiration. The combination of CO2 and +NP significantly increased electron transport rates in both species. While +NP alone stimulated H. opuntia growth rates, Dictyota growth was significantly stimulated by nutrient enrichment only at elevated CO2, which led to the highest biomass ratios of Dictyota to Halimeda. Our results suggest that inorganic nutrient enrichment alone stimulates several aspects of H. opuntia physiology, but nutrient enrichment at a CO2 concentration predicted for the end of the century benefits Dictyota sp. and hinders its calcifying basibiont H. opuntia.
authors: Marine Botany, Bremen Marine Ecology Centre for Research and Education, University of Bremen, Leobener Str. NW2, 28359, Bremen, Germany, laurie.c.hofmann@gmail.com.
authors: Laurie C
authors: LC
authors: Hofmann
authors: Kai
authors: K
authors: Bischof
authors: Cecilia
authors: C
authors: Baggini
authors: Andrew
authors: A
authors: Johnson
authors: Ketil
authors: K
authors: Koop-Jakobsen
authors: Mirta
authors: M
authors: Teichberg
mesh_terms: D018533:Biomass; D002118:Calcium / Q000378:metabolism; D002119:Calcium Carbonate / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D000460:Chlorophyta / Q000145:classification / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D017753:Ecosystem; D004579:Electron Transport; D005068:Eutrophication; D009566:Nitrates / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D010788:Photosynthesis; D013045:Species Specificity; D014877:Water Pollution, Chemical
chemical_list: D009566:Nitrates; D010710:Phosphates; D002245:Carbon Dioxide; D010758:Phosphorus; D002119:Calcium Carbonate; D009584:Nitrogen; D010100:Oxygen; D002118:Calcium
references: Oecologia. 1992 Apr;89(4):464-470
references: 28311874
references: Mar Pollut Bull. 2002 Nov;44(11):1194-205
references: 12523518
references: Oecologia. 2013 Jun;172(2):575-83
references: 23111809
references: J Photochem Photobiol B. 2003 Jan;69(1):21-30
references: 12547493
references: Oecologia. 1992 Sep;91(3):377-384
references: 28313546
references: Planta. 2001 May;213(1):64-70
references: 11523657
references: Oecologia. 1986 Jul;69(4):628-630
references: 28311627
references: Science. 1984 Jan 27;223(4634):405-7
references: 17829890
references: PeerJ. 2014 May 27;2:e411
references: 24918033
references: Science. 2007 Dec 14;318(5857):1737-42
references: 18079392
references: Science. 1975 Apr 18;188(4185):257-9
references: 17800402
references: PLoS One. 2012;7(3):e33841
references: 22439005