, Volume 176, Issue 3, pp 871–882 | Cite as

Seagrass response to CO2 contingent on epiphytic algae: indirect effects can overwhelm direct effects

  • Owen W. BurnellEmail author
  • Bayden D. Russell
  • Andrew D. Irving
  • Sean D. Connell
Global change ecology - Original research


Increased availability of dissolved CO2 in the ocean can enhance the productivity and growth of marine plants such as seagrasses and algae, but realised benefits may be contingent on additional conditions (e.g. light) that modify biotic interactions between these plant groups. The combined effects of future CO2 and differing light on the growth of seagrass and their algal epiphytes were tested by maintaining juvenile seagrasses Amphibolis antarctica under three different CO2 concentrations representing ambient, moderate future and high future forecasts (i.e. 390, 650 vs. 900 µl l−1) and two light levels representing low and high PAR (i.e. 43 vs. 167 µmol m−2 s−1). Aboveground and belowground biomass, leaf growth, epiphyte cover, tissue chemistry and photosynthetic parameters of seagrasses were measured. At low light, there was a neutral to positive effect of elevated CO2 on seagrass biomass and growth; at high light, this effect of CO2 switched toward negative, as growth and biomass decreased at the highest CO2 level. These opposing responses to CO2 appeared to be closely linked to the overgrowth of seagrass by filamentous algal epiphytes when high light and CO2 were combined. Importantly, all seagrass plants maintained positive leaf growth throughout the experiment, indicating that growth was inhibited by some experimental conditions but not arrested entirely. Therefore, while greater light or elevated CO2 provided direct physiological benefits for seagrasses, such benefits were likely negated by overgrowth of epiphytic algae when greater light and CO2 were combined. This result demonstrates how indirect ecological effects from epiphytes can modify independent physiological predictions for seagrass associated with global change.


Amphibolis antarctica Biotic interactions Filamentous epiphytes Global change Photosynthesis 



We would like to thank Nenah Mackenzie from The University of Adelaide for operating the mass spectrometer. S.D.C. and B.D.R. were funded by an ARC grant and S.D.C. received an ARC Future Fellowship. We would also like to thank two anonymous reviewers and the Associate Editor, whose comments improved an early draft of the manuscript.

Conflict of interest

The authors have no conflicts of interest to declare.

Supplementary material

442_2014_3054_MOESM1_ESM.docx (38 kb)
Table S1 ANOVA comparing the effects of CO2 and light on the biomass of calcified epiphytic algae on juvenile seagrass Amphibolis antarctica after 12 weeks. ACO 2  ambient CO2, MCO 2  moderate CO2, HCO 2  high CO2. Significant effects from ANOVA are highlighted in bold Fig. S1 Average hourly photosynthetically active radiation (PAR in µmol m−2 s−1) over 24 h for 12 weeks at different light treatments. Closed circles low light, open circles high light. Data points represent the mean ± SE (n = 84) Fig. S2a–b Calcified epiphytic algae on a shed leaves and b living plants of juvenile seagrass grown at different CO2 and light levels for 12 weeks. ACO 2  ambient CO2, MCO 2  moderate CO2, HCO 2  high CO2, LL low light, HL high light. Bars represent the mean ± SE (n = 6). Fig. S3a–b Regression analysis showing a total seagrass biomass (aboveground + belowground) vs.  % N in seagrass tissue, and b total epiphyte biomass (filamentous algae + calcified algae) vs.  % N in seagrass tissue. Linear regression analysis for total seagrass biomass (r 2 = 0.280, F 1,35 = 13.24, P < 0.001) and total epiphyte biomass (r 2 = 0.378, F 1,35 = 20.70, P < 0.001) (DOCX 38 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Owen W. Burnell
    • 1
    Email author
  • Bayden D. Russell
    • 1
  • Andrew D. Irving
    • 2
  • Sean D. Connell
    • 1
  1. 1.Southern Seas Ecology Laboratories, Darling Building (DP418), School of Earth and Environmental SciencesUniversity of AdelaideAdelaideAustralia
  2. 2.School of Medical and Applied SciencesCentral Queensland UniversityRockhamptonAustralia

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