Seagrass meadows mixed with calcareous algae have higher plant productivity and sedimentary blue carbon storage

Abstract

Seagrass meadows capture and store large amounts of carbon in the sediment beneath, thereby serving as efficient sinks of atmospheric CO2. Carbon sequestration levels may however differ greatly among meadows depending on, among other factors, the plant community composition. Tropical seagrass meadows are often intermixed with macroalgae, many of which are calcareous, which may compete with seagrass for nutrients, light, and space. While the photosynthetic CO2 uptake by both seagrasses and calcareous algae may increase the overall calcification in the system (by increasing the calcium carbonate saturation state, Ω), the calcification process of calcareous algae may lead to a release of CO2, thereby affecting both productivity and calcification, and eventually also the meadows’ carbon storage. This study estimated how plant productivity, CaCO3 production, and sediment carbon levels were affected by plant community composition (seagrass and calcareous algae) in a tropical seagrass‐dominated embayment (Zanzibar, Tanzania). Overall, the patterns of variability in productivity differed between the plant types, with net areal biomass productivity being highest in meadows containing both seagrass and calcareous algae. Low and moderate densities of calcareous algae enhanced seagrass biomass growth, while the presence of seagrass reduced the productivity of calcareous algae but increased their CaCO3 content. Sedimentary carbon levels were highest when seagrasses were mixed with low or moderate cover of calcareous algae. The findings show that plant community composition can be an important driver for ecosystem productivity and blue carbon sequestration.

Photosynthetic Toxicity of Enrofloxacin on Scenedesmus obliquus in an Aquatic Environment

“…The maximum reduction rates observed in the 10 µg/L treatment group could be attributed to the negligible damage to algae at a low concentration of ENR, consistent with the results obtained for the GIR of S. obliquus. For this reason, many researchers have used algae to clean water that has been slightly contaminated with antibiotics based on their uptake and metabolic ability [7,8].…”

“…As a basic type of biomass, algae are able to conduct photosynthesis, synthetize organic matter, and play an important role in carbon storage in aquatic environments [5,6]. For instance, lightly or moderately calcareous algae could help seagrasses store sedimentary carbon and greatly improve blue carbon sequestration [7,8]. Moreover, as the main producer in freshwater, algae are essential in providing energy to higher living organisms.…”

Carbon sequestration and climate change mitigation using macroalgae: a state of knowledge review

“…This suggests that other processes may be responsible for changes in alkalinity within macroalgal forests (Koweek et al ., 2017), or that CO 2 released by calcification can be immediately fixed. This would constitute a positive feedback whereby macroalgae favour calcification which, in turn, provides CO 2 for photosynthesis (Kalokora et al ., 2022). The ultimate effect of carbonate precipitation on CO 2 emissions will depend on whether the dissolved CO 2 is released to the atmosphere, as well as on the long‐term fate of the carbonate retained in sea water.…”