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. 2023 Nov 17;18(11):e0286661.
doi: 10.1371/journal.pone.0286661. eCollection 2023.

Effects of ocean acidification on growth and photophysiology of two tropical reef macroalgae

Heather N Page  1   2 , Sophie McCoy  3 , Robert G M Spencer  4 , Katherine A Burnham  1 , Clay Hewett  1   5 , Maggie Johnson  6
Affiliations

Effects of ocean acidification on growth and photophysiology of two tropical reef macroalgae

Heather N Page et al. PLoS One. .

Abstract

Macroalgae can modify coral reef community structure and ecosystem function through a variety of mechanisms, including mediation of biogeochemistry through photosynthesis and the associated production of dissolved organic carbon (DOC). Ocean acidification has the potential to fuel macroalgal growth and photosynthesis and alter DOC production, but responses across taxa and regions are widely varied and difficult to predict. Focusing on algal taxa from two different functional groups on Caribbean coral reefs, we exposed fleshy (Dictyota spp.) and calcifying (Halimeda tuna) macroalgae to ambient and low seawater pH for 25 days in an outdoor experimental system in the Florida Keys. We quantified algal growth, calcification, photophysiology, and DOC production across pH treatments. We observed no significant differences in the growth or photophysiology of either species between treatments, except for lower chlorophyll b concentrations in Dictyota spp. in response to low pH. We were unable to quantify changes in DOC production. The tolerance of Dictyota and Halimeda to near-future seawater carbonate chemistry and stability of photophysiology, suggests that acidification alone is unlikely to change biogeochemical processes associated with algal photosynthesis in these species. Additional research is needed to fully understand how taxa from these functional groups sourced from a wide range of environmental conditions regulate photosynthesis (via carbon uptake strategies) and how this impacts their DOC production. Understanding these species-specific responses to future acidification will allow us to more accurately model and predict the indirect impacts of macroalgae on coral health and reef ecosystem processes.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Photophysiology of Dictyota and Halimeda after 25 days of exposure to ambient pH (blue) and low pH (orange) conditions.
Data are mean ± 1 sd. Asterisk indicates statistically significant differences (p< 0.05) between ambient and low pH treatments.
See this image and copyright information in PMC

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