Elevated CO2 Leads to Enhanced Photosynthesis but Decreased Growth in Early Life Stages of Reef Building Coralline Algae

Crustose coralline algae (CCA) are key organisms in coral reef ecosystems, where they contribute to reef building and substrate stabilization. While ocean acidification due to increasing CO2 can affect the biology, physiology and ecology of fully developed CCA, the impacts of elevated CO2 on the ear...

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Bibliographic Details
Published in:Frontiers in Marine Science
Main Authors: Alexandra Ordoñez, Daniel Wangpraseurt, Niclas Heidelberg Lyndby, Michael Kühl, Guillermo Diaz-Pulido
Format: Article in Journal/Newspaper
Language:English
Published: Frontiers Media S.A. 2019
Subjects:
ocean acidification
global warming
early stages
red algae
algal physiology
photosynthesis
Science
Q
General. Including nature conservation
geographical distribution
QH1-199.5
Ocean acidification
Online Access:https://doi.org/10.3389/fmars.2018.00495
https://doaj.org/article/1b7a58bf4f0e41ad81afd723a7d2a299
Description
Summary:Crustose coralline algae (CCA) are key organisms in coral reef ecosystems, where they contribute to reef building and substrate stabilization. While ocean acidification due to increasing CO2 can affect the biology, physiology and ecology of fully developed CCA, the impacts of elevated CO2 on the early life stages of CCA are much less explored. We assessed the photosynthetic activity and growth of 10-day-old recruits of the reef-building crustose coralline alga Porolithon cf. onkodes exposed to ambient and enhanced CO2 seawater concentration causing a downward shift in pH of ∼0.3 units. Growth of the CCA was estimated using measurements of crust thickness and marginal expansion, while photosynthetic activity was studied with O2 microsensors. We found that elevated seawater CO2 enhanced gross photosynthesis and respiration, but significantly reduced vertical and marginal growth of the early life stages of P. cf. onkodes. Elevated CO2 stimulated photosynthesis, particularly at high irradiance, likely due to increased availability of CO2, but this increase did not translate into increased algal growth as expected, suggesting a decoupling of these two processes under ocean acidification scenarios. This study confirms the sensitivity of early stages of CCA to elevated CO2 and identifies complexities in the physiological processes underlying the decreased growth and abundance in these important coral reef builders upon ocean acidification.

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