Sinking seaweed in the deep ocean for carbon neutrality is ahead of science and beyond the ethics

Sinking vast amounts of seaweed in the deep ocean is currently being proposed as a promising ocean carbon dioxide removal strategy as well as a natural-based solution to mitigate climate change. Still, marketable carbon offsets through large-scale seaweed sinking in the deep ocean lack documentation and could involve unintended environmental and social consequences. Managing the risks requires a number of urgent actions

Sinking seaweed in the deep ocean for carbon neutrality is ahead of science and beyond the ethics

Unidad de excelencia María de Maeztu CEX2019-000940-MSinking vast amounts of seaweed in the deep ocean is currently being proposed as a promising ocean carbon dioxide removal strategy as well as a natural-based solution to mitigate climate change. Still, marketable carbon offsets through large-scale seaweed sinking in the deep ocean lack documentation and could involve unintended environmental and social consequences. Managing the risks requires a number of urgent actions

High variability of Blue Carbon storage in seagrass meadows at the estuary scale

Seagrass meadows are considered important natural carbon sinks due to their capacity to store organic carbon (Corg) in sediments. However, the spatial heterogeneity of carbon storage in seagrass sediments needs to be better understood to improve accuracy of blue carbon assessments, particularly when strong gradients are present. We performed an intensive coring study within a sub-tropical estuary to assess the spatial variability in sedimentary Corg associated with seagrasses, and to identify the key factors promoting this variability. We found a strong spatial pattern within the estuary, from 52.16 mg Corg cm-3 in seagrass meadows in the upper parts, declining to 1.06 mg Corg cm-3 in seagrass meadows at the estuary mouth, despite a general gradient of increasing seagrass cover and seagrass habitat extent in the opposite direction. The sedimentary Corg underneath seagrass meadows came principally from allochthonous (non-seagrass) sources (~70-90%), while the contribution of seagrasses was low (~10-30%) throughout the entire estuary. Our results showed that Corg stored in sediments of seagrass meadows can be highly variable within an estuary, attributed largely to accumulation of fine sediments and inputs of allochthonous sources. Local features and the existence of spatial gradients must be considered in blue carbon estimates in coastal ecosystems

Comunidades de peces del atolón de Clipperton (Pacífico oriental tropical) y su relación con la cobertura de corales

Clipperton Atoll, one of the most isolated coral reefs worldwide, is of great scientific interest due to its geomorphology and high levels of endemism. This study explored the reef fish assemblage structure of Clipperton Atoll and its relationship with live coral cover. Nine stations were sampled at three sites and three depths (6, 12 and 20 m) around the reef, measuring fish species richness and biomass and hermatypic coral cover (at genus level). We evaluated variation in species richness, biomass and diversity of fish assemblages among sites and depths, as well as the relationship between the entire fish assemblage composition and live coral cover. The results showed that species richness and biomass were similar among sites, but differed across depths, increasing with depth. In contrast, diversity differed among sites but not among depths. Multivariate analyses indicated that fish assemblage composition differed among sites and depths in relation to changes in cover of coral of the genera Pocillopora, Porites, Pavona and Leptoseris, which dominate at different depths. The results showed that fish species richness and diversity were low at Clipperton Atoll and that, in isolated coral reefs with a low habitat heterogeneity and low human disturbance, live coral cover has a significant influence on the spatial variation of the reef fish assemblages. This study highlights the importance of coral habitat structure in shaping coral reef fish assemblages.El atolón de Clipperton, uno de los arrecifes de coral más aislados del mundo, presenta un gran interés científico por su geomorfología y endemismo. Este estudio analizó la estructura de las comunidades de peces de arrecife de este atolón y su relación con la cobertura de coral vivo. Para ello se muestrearon nueve estaciones alrededor del arrecife en tres sitios a tres profundidades (6, 12, 20 m), registrando, la riqueza y biomasa de peces, así como la cobertura de coral hermatípico a nivel de género. Se evaluó la variación de la riqueza, biomasa y diversidad de peces entre sitios y profundidades, así como la relación de la composición y biomasa de peces con la cobertura de coral vivo. Los resultados mostraron que la riqueza y biomasa fueron similares entre los sitios, pero diferentes entre profundidades, ya que incrementan con la profundidad. En contraste, la diversidad difirió entre sitios pero no entre profundidades. Los análisis multidimensionales indicaron que la comunidad de peces fue diferente entre sitios y profundidades, relacionándolo con la cobertura de coral de los géneros Pocillopora, Porites, Pavona y Leptoseris, que dominan a distinta profundidad. Los resultados evidenciaron una baja riqueza y diversidad de peces arrecifales en el atolón de Clipperton. En arrecifes de coral aislados, con baja heterogeneidad de hábitats y poca perturbación humana, la cobertura de coral vivo influye en la variación espacial de las comunidades de peces arrecifales. Este estudio resalta la importancia de la estructura del hábitat de coral en la conformación de las comunidades de peces arrecifales

Assessing the risk of carbon dioxide emissions from blue carbon ecosystems

“Blue carbon” ecosystems, which include tidal marshes, mangrove forests, and seagrass meadows, have large stocks of organic carbon (Corg) in their soils. These carbon stocks are vulnerable to decomposition and – if degraded – can be released to the atmosphere in the form of CO2. We present a framework to help assess the relative risk of CO2 emissions from degraded soils, thereby supporting inclusion of soil Corg into blue carbon projects and establishing a means to prioritize management for their carbon values. Assessing the risk of CO2 emissions after various kinds of disturbances can be accomplished through knowledge of both the size of the soil Corg stock at a site and the likelihood that the soil Corg will decompose to CO2

Key biogeochemical factors affecting soil carbon storage in Posidonia meadows

Unidad de excelencia María de Maeztu MdM-2015-0552Biotic and abiotic factors influence the accumulation of organic carbon (Corg) in seagrass ecosystems. We surveyed Posidonia sinuosa meadows growing in different water depths to assess the variability in the sources, stocks and accumulation rates of Corg. We show that over the last 500 years, P. sinuosa meadows closer to the upper limit of distribution (at 2-4m depth) accumulated 3- to 4-fold higher Corg stocks (averaging 6.3 kg Corg m¯²/ at 3- to 4-fold higher rates (12.8 gCorg m¯² yr¯¹/ compared to meadows closer to the deep limits of distribution (at 6-8m depth; 1.8 kg Corg m¯² and 3.6 g Corg m¯² yr¯¹/. In shallower meadows, Corg stocks were mostly derived from seagrass detritus (88% in average) compared to meadows closer to the deep limit of distribution (45% on average). In addition, soil accumulation rates and fine-grained sediment content (< 0.125 mm) in shallower meadows (2.0mm yr¯¹ and 9 %, respectively) were approximately 2-fold higher than in deeper meadows (1.2mm yr¯¹ and 5 %, respectively). The Corg stocks and accumulation rates accumulated over the last 500 years in bare sediments (0.6 kg Corg m¯² and 1.2 g Corg m¯² yr¯¹/ were 3- to 11-fold lower than in P. sinuosa meadows, while fine-grained sediment content (1 %) and seagrass detritus contribution to the Corg pool (20 %) were 8- and 3-fold lower than in Posidonia meadows, respectively. The patterns found support the hypothesis that Corg storage in seagrass soils is influenced by interactions of biological (e.g., meadow productivity, cover and density), chemical (e.g., recalcitrance of Corg stocks) and physical (e.g., hydrodynamic energy and soil accumulation rates) factors within the meadow. We conclude that there is a need to improve global estimates of seagrass carbon storage accounting for biogeochemical factors driving variability within habitats

La desaparició dels boscos submarins pot portar a la pèrdua de biodiversitat, la disminució de la qualitat de l'aigua i la desprotecció de la costa

[EN] In this May's "In Depth" we interview Aurora M Ricart, who has just landed at the ICM-CSIC to delve deeper into the effects of climate crisis on marine ecosystems, but specifically on underwater forests[ES] En el "A fondo" de este mes de mayo entrevistamos a Aurora M Ricart, que acaba de aterrizar en el ICM-CSIC con el objetivo de estudiar el impacto de la crisis climática sobre los ecosistemas marinos, pero especialmente sobre los bosques marinos[CAT] A l'”A fons” d'aquest mes de maig entrevistem l’Aurora M Ricart, que acaba d'aterrar a l'ICM-CSIC amb l’objectiu d’estudiar l'impacte de la crisi climàtica sobre els ecosistemes marins, però especialment sobre els boscos marinsPeer reviewe