Effects of Ocean Acidification and Temperature Increases on the Photosynthesis of Tropical Reef Calcified Macroalgae.

Fernando Scherner,Sonia Maria Barreto Pereira,Cristiano Macedo Pereira,José Bonomi Barufi,Paulo Antunes Horta,Gustavo Duarte,Clovis Barreira E Castro,Inés Álvarez

doi:10.1371/journal.pone.0154844

Abstract

Climate change is a global phenomenon that is considered an important threat to marine ecosystems. Ocean acidification and increased seawater temperatures are among the consequences of this phenomenon. The comprehension of the effects of these alterations on marine organisms, in particular on calcified macroalgae, is still modest despite its great importance. There are evidences that macroalgae inhabiting highly variable environments are relatively resilient to such changes. Thus, the aim of this study was to evaluate experimentally the effects of CO2-driven ocean acidification and temperature rises on the photosynthesis of calcified macroalgae inhabiting the intertidal region, a highly variable environment. The experiments were performed in a reef mesocosm in a tropical region on the Brazilian coast, using three species of frondose calcifying macroalgae (Halimeda cuneata, Padina gymnospora, and Tricleocarpa cylindrica) and crustose coralline algae. The acidification experiment consisted of three treatments with pH levels below those occurring in the region (-0.3, -0.6, -0.9). For the temperature experiment, three temperature levels above those occurring naturally in the region (+1, +2, +4°C) were determined. The results of the acidification experiment indicate an increase on the optimum quantum yield by T. cylindrica and a decline of this parameter by coralline algae, although both only occurred at the extreme acidification treatment (-0.9). The energy dissipation mechanisms of these algae were also altered at this extreme condition. Significant effects of the temperature experiment were limited to an enhancement of the photosynthetic performance by H. cuneata although only at a modest temperature increase (+1°C). In general, the results indicate a possible photosynthetic adaptation and/or acclimation of the studied macroalgae to the expected future ocean acidification and temperature rises, as separate factors. Such relative resilience may be a result of the highly variable environment they inhabit.

Highlights

Climate change is a key global threat to ocean ecosystems [1, 2]
According to the Intergovernmental Panel on Climate Change (IPCC) seawater warming and ocean acidification are still beginning in relation to the most negative scenarios forecasted by climatologists [7]
Our experiments have shown little effects of acidification and temperature rises on the tested species and groups

Summary

Introduction

Climate change is a key global threat to ocean ecosystems [1, 2]. Changes in ocean chemistry and seawater warming associated with increasing greenhouse gas concentrations have potential to affect the physiology of marine organisms [3] causing food webs changes [4] and leading to drastic shifts in marine communities [5]. Understanding the physiological and ecological effects of ocean acidification and increased temperatures on marine organisms is fundamental to predict future changes and assist with new management challenges of marine ecosystems. Marine macroalgae are an important component of coastal ecosystems, supporting a high biodiversity and forming the base of marine food webs [8]. Despite their great ecological importance, little attention has been given to the effects of climate change on macroalgae [6]. The experimental effort that has been devoted to understand the physiological responses of calcifying algae to ocean acidification and sea temperature increases is still relatively modest and focused mainly in coralline species, with little attention given to other important calcifying macroalgae groups. There is an urgent need for research on calcifying macroalgae responses to climate change [10]

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Results

Conclusion