Influence of the seagrass Thalassia hemprichii on coral reef mesocosms exposed to ocean acidification and experimentally elevated temperatures

• Published in: The Science of the total environment Vol. 700; p. 134464
• Main Authors: Liu, Pi-Jen, Ang, Shin-Jing, Mayfield, Anderson B., Lin, Hsing-Juh
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.01.2020
• Subjects: Animals; Anthozoa - physiology; calcification; Climate Change; Coral Reefs; corals; Ecosystem metabolism; Ecosystem production; ecosystem respiration; environment; gross primary productivity; Hydrocharitaceae - physiology; Hydrogen-Ion Concentration; leaves; macroalgae; net ecosystem production; Ocean acidification; photosynthesis; Seagrass; seagrasses; Seawater - chemistry; Temperature; Thalassia hemprichii; Coral reefs; Climate change; Ecosystem metabolism; Seagrass; Ocean acidification; Ecosystem production
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.134464

Conceptual model of climate change (ocean acidification [OA] and seawater warming) effects on coral reef mesocosms that either do (light blue) or do not (blue) feature seagrass beds. Solid lines denote abiotic effects (i.e., OA or OA + warming to 31C), whereas dotted lines depict effects of co-incubation with seagrass. CCM = carbon concentrating mechanism. ER=ecosystem respiration, GPP = gross primary production, NEP = net ecosystem metabolism, and P/R = photosynthesis/respiration ratio. [Display omitted] •The combined effect of OA and rising temperatures stimulated the growth of macroalgae.•OA resulted in higher coral calcification rates when corals were co-incubated with seagrass.•Macroalgal growth was lower in seagrass-containing mesocosms.•Coral and macroalgal, but not seagrass, growth suffered at 31 °C under OA conditions.•Seagrass helped to stabilize the system’s metabolism in response to projected climate change stressors. Ocean acidification (OA) and warming currently threaten coastal ecosystems across the globe. However, it is possible that the former process could actually benefit marine plants, such as seagrasses. The purpose of this study was to examine whether the effects of the seagrass Thalassia hemprichii can increase the resilience of OA-challenged coral reef mesocosms whose temperatures were gradually elevated. It was found that seagrass shoot density, photosynthetic efficiency, and leaf growth rate actually increased with rising temperatures under OA. Macroalgal growth rates were higher in the seagrass-free mesocosms, but the calcification rate of the model reef coral Pocillopora damicornis was higher in coral reef mesocosms featuring seagrasses under OA at 25 and 28 °C. Both the macroalgal growth rate and the coral calcification rate decreased in all mesocosms when the temperature was raised to 31 °C under OA. However, the variation in gross primary production, ecosystem respiration, and net ecosystem production in the seagrass mesocosms was lower than in seagrass-free controls, suggesting that the presence of seagrass in the mesocosms helped to stabilize the metabolism of the system in response to simulated climate change.