Warming intensify CO₂ flux and nutrient release from algal wrack subsidies on sandy beaches

Abstract

Algal wrack subsidies underpin most of the food web structure of exposed sandy beaches and are responsible of important biogeochemical processes that link marine and terrestrial ecosystems. The response in decomposition of algal wrack deposits to global warming has not been studied in ocean-exposed sandy beaches to date. With this aim, passive open top chambers (OTCs) were used to increase soil temperature within the range predicted by the IPCC for western Europe (between 0.5 and 1.5°C), following the hypothesis that the biogeochemical processing of macroalgal wrack subsidies would accelerate in response to temperature increase. The effect of temperature manipulation on three target substrates: fresh and aged macroalgae, and bare sand, was tested. Results indicated that a small warming (<0.5°C) affected the wrack decomposition process through traceable increases in soil respiration through CO flux, inorganic nutrients within the interstitial environment (N and P), sediment organic contents measured through the amount of proteins and microbial pool through the total soil DNA. The different responses of soil variables in the studied substrates indicated that the decomposition stage of stranded macroalgae influences the biogeochemical processing of organic matter in sandy beaches. Thus, CO fluxes, releases of organic and inorganic nutrients and microbial activity intensify in aged wrack deposits. Our results predict that expected global warming will increase the release of inorganic nutrients to the coastal ocean by 30% for the N (21 Gg/year) and 5.9% for P (14 Gg/year); that increase for the flow of C to the atmosphere as CO was estimated in 8.2% (523 Gg/year). This study confirms the key role of sandy beaches in recycling ocean-derived organic matter, highlighting their sensitivity to a changing scenario of global warming that predicts significant increases in temperature over the next few decades.

Degradation of macroalgal detritus in shallow coastal Antarctic sediments

“…Even in cold environments with oxygen-rich waters such as those present in Potter Cove, macroalgal decay in sediments can locally lead to hypoxic conditions in the surface sediments (Pasotti et al 2014;Hoffmann et al 2018). With increases in water temperature as a result of global warming, the microbial degradation of macroalgal detritus could be intensified, increasing respiration and the release of nutrients (Lastra et al 2018). This can have a severe influence on the oxygen availability for sediment-inhabiting fauna and the nutrient content at the sediment-water interface.…”

The role of inputs of marine wrack and carrion in sandy‐beach ecosystems: a global review

“…Similarly, wrack on beaches can be three times more metabolically active than subtidal seagrass or macroalgal beds (e.g. Coupland et al ., 2007 ; Lastra, López & Rodil, 2018 ; Liu et al ., 2019 ). By contrast, methane emissions from wrack appear to be negligible, at least under dry conditions (Liu et al ., 2019 ), despite wrack having a demonstrated potential for biogas production (Kaspersen et al ., 2016 ; Misson et al ., 2020 ).…”

Flotsam and jetsam: a global review of the role of inputs of marine organic matter in sandy beach ecosystems

“…Similarly, wrack on beaches can be three times more metabolically active than subtidal seagrass or macroalgal beds (e.g. Coupland et al, 2007;Lastra et al, 2018;Liu et al, 2019). In contrast, methane emissions from wrack appear to be negligible (Liu et al, 2019), despite wrack having a demonstrated potential for biogas production (Kaspersen et al, 2016;Misson et al, 2020).…”