Abstract
The combination of ocean acidification (OA) and global warming is expected to have a significant effect on the diversity and functioning of marine ecosystems, particularly on calcifying algae such as rhodoliths (maërl) that form extensive beds worldwide, from polar to tropical regions. In addition, the increasing frequency of extreme events, such as heat waves, threatens coastal ecosystems and may affect their capacity to fix blue carbon. The few studies where the simultaneous effects of both temperature and CO2 were investigated have revealed contradictory results. To assess the effect that high temperature spells can have on the maërl beds under OA, we tested the short‐time effects of temperature and CO2 on the net photosynthesis, respiration, and calcification of the recently described species Phymatolithon lusitanicum, the most common maërl species of southern Portugal. Photosynthesis, calcification, and respiration increased with temperature, and the differences among treatments were enhanced under high CO2. We found that in the short term, the metabolic rates of Phymatolithon lusitanicum will increase with CO2 and temperature as will the coupling between calcification and photosynthesis. However, under high CO2, this coupling will favor photosynthesis over calcification, which, in the long term, can have a negative effect on the blue carbon fixing capacity of the maërl beds from southern Portugal.
Highlights
Between 1750 and 2000, the world's oceans have absorbed about one‐third of all the carbon dioxide (CO2) emitted by humans (Zeebe & Ridgwell, 2011)
We found a positive interaction between CO2 and temperature for all the metabolic rates of Phymatolithon lusitanicum, with tempera‐ ture being the factor that contributed the most to the differences observed on photosynthesis, light calcification, and respiration of the algae, while CO2 was the determinant factor on dark calcifica‐ tion
The response of Phymatolithon lusitanicum to increasing temperature is amplified by increasing CO2
Summary
Between 1750 and 2000, the world's oceans have absorbed about one‐third of all the carbon dioxide (CO2) emitted by humans (Zeebe & Ridgwell, 2011). At an unprecedented rate in geologi‐ cal history, atmospheric CO2 has risen from 280 ppm in 1750 to more than 400 ppm in 2016 (Betts et al, 2018) An increase in the fre‐ quency of extreme events, such as heat waves, threatens coastal ecosystems and their capacity to fix blue carbon (Arias‐Ortiz et al, 2018). Heat waves are becoming more fre‐ quent and extreme. This is expected to have an irreversible impact on marine organisms and push coastal ecosystems to the limits of their resilience (Frölicher, Fischer, & Gruber, 2018). There is an important gap of information on the effect that these rapid temperature changes will have on the metabolism of tem‐ perate maërl beds
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call