Warming enhances carbon dioxide and methane fluxes from Red Sea seagrass (<i>Halophila stipulacea</i>) sediments

Abstract

Abstract. Seagrass meadows are autotrophic ecosystems acting as carbon sinks, but they have also been shown to be sources of carbon dioxide (CO2) and methane (CH4). Seagrasses can be negatively affected by increasing seawater temperatures, but the effects of warming on CO2 and CH4 fluxes in seagrass meadows have not yet been reported. Here, we examine the effect of two disturbances on air–seawater fluxes of CO2 and CH4 in Red Sea Halophila stipulacea communities compared to adjacent unvegetated sediments using cavity ring-down spectroscopy. We first characterized CO2 and CH4 fluxes in vegetated and adjacent unvegetated sediments, and then experimentally examined their response, along with that of the carbon (C) isotopic signature of CO2 and CH4, to gradual warming from 25 ∘C (winter seawater temperature) to 37 ∘C, 2 ∘C above current maximum temperature. In addition, we assessed the response to prolonged darkness, thereby providing insights into the possible role of suppressing plant photosynthesis in supporting CO2 and CH4 fluxes. We detected 6-fold-higher CO2 fluxes in vegetated compared to bare sediments, as well as 10- to 100-fold-higher CH4 fluxes. Warming led to an increase in net CO2 and CH4 fluxes, reaching average fluxes of 10 422.18 ± 2570.12 µmol CO2 m−2 d−1 and 88.11±15.19 µmol CH4 m−2 d−1, while CO2 and CH4 fluxes decreased over time in sediments maintained at 25 ∘C. Prolonged darkness led to an increase in CO2 fluxes but a decrease in CH4 fluxes in vegetated sediments. These results add to previous research identifying Red Sea seagrass meadows as a significant source of CH4, while also indicating that sublethal warming may lead to increased emissions of greenhouse gases from seagrass meadows, providing a feedback mechanism that may contribute to further enhancing global warming.

Blue carbon as a natural climate solution

“…An unprecedented heatwave in 2010-2011 led to a 22% loss of seagrass cover in Shark Bay, Australia, resulting in an estimated increase in national CO 2 emissions from land-use change by 4-21% per annum 93 . Experimentally increasing the temperature up to 37 °C led to a fourfold increase in methane fluxes if compared with the community held at 25 °C from Red Sea seagrass sediments 143 . Temperature increase is likely to lead to a range of different responses in BCEs, including an increase or decrease in primary productivity, faster decomposition of organic matter and changes in BCE spatial distribution, but there are still many uncertainties regarding the nature and extent of these changes and how they might differ with latitude and environmental setting 108,118 .…”

“…Positive steps can be taken to mitigate sea-level rise through restoration projects that include a mix of species and at increased densities and scale, while taking into account local hydrology, the potential for landward 0123456789();: expansion of mangroves and tidal marshes, and relevance to the socio-economic factors affecting the local communities 109,111,141,142 . Anthropogenic warming can also have an impact; for example, increasing temperatures can result in changing gas fluxes in BCEs that lead to enhanced emissions 93,118,143 . The effect of temperature increase on greenhouse gas emissions in seagrass meadows has indicated the potential negative effects of climate change.…”

Methane emission and sulfide levels increase in tropical seagrass sediments during temperature stress: A mesocosm experiment

“…How seagrass systems might contribute to these emissions has received comparably little attention, although valuable studies have been published (Bahlmann et al, ; Barber & Carlson, ; Deborde et al, ; Garcias‐Bonet & Duarte, ; Oremland, ). Temperature increases have been shown to enhance methane emissions from freshwater systems (Yvon‐Durocher, Hulatt, Woodward, & Trimmer, ; Yvon‐Durocher, Montoya, Woodward, Jones, & Trimmer, ), and recently, it has been shown that methane emission from seagrass meadows rises substantially when seagrasses are disturbed (Burkholz, Garcias‐Bonet, & Duarte, ; Lyimo et al, ), and based on calculations of methane emission in seagrass sediments from the Red Sea, it has been suggested that the present estimations of methane emissions from natural systems might have to be increased by about 30% to account for hitherto unrecognized contributions from seagrass systems (Garcias‐Bonet & Duarte, ). In general, the methane production of biological systems is closely correlated with the productivity of the plants within the system (Borges, Speeckaert, Champenois, Scranton, & Gypens, ; Bridgham et al, ), and for wetlands in particular, there is a clear positive correlation between emission of methane and net ecosystem production (Whiting & Chanton, ).…”

Methane Emissions From Nordic Seagrass Meadow Sediments

“…This is substantially lower than what has been observed in other marine habitats; for example, saltmarshes can emit over 10,000 µg m −2 h −1 (Whiting and Chanton, 1993). However, stressors (such as light reduction, habitat fragmentation, and warming) can dramatically increase CH 4 emission in seagrass systems (Lyimo et al, 2018;Burkholz et al, 2020;George et al, 2020). Vegetation loss or alteration in macrophyte species composition may also stimulate methanogenesis in the sediment (Sutton-Grier and Megonigal, 2011;Lyimo et al, 2018;Al-Haj and Fulweiler, 2020).…”