Anna Lafratta

Crucial for coastal carbon sequestration, global seagrass organic carbon (OC) burial rates remain uncertain as early estimates were derived from mixed methodologies across geographically and taxonomically biased datasets. Here, we present a data-driven reassessment from a synthesis of 332 sediment cores spanning the last century. Results show that seagrasses bury OC at 25 ± 3 g OC m ⁻² yr ⁻¹ (geometric mean), with an area-weighted global average of 33 ± 9 g OC m ⁻² yr ⁻¹ . Rates reflect a balance between sediment OC content and sediment accumulation, which share a negative exponential relationship driven by mineral dilution. Based on a revised mapped seagrass extent (247,700–366,400 km ² ), global burial scales to 6–15 Tg C yr ⁻¹ . Although one-fourth of earlier benchmarks, seagrasses account for 3–4% to 3–6% of total oceanic OC burial despite covering <0.1% of the seafloor. Combined with mangroves and tidal marshes, vegetated coastal ecosystems contribute 8–13% of oceanic OC burial.

Blue carbon ecosystems, classically defined as mangroves, tidal marshes and seagrasses, but increasingly expanded to include ecosystems such as tidal flats, macroalgal forests and shelf sediments, contribute to climate change mitigation and biodiversity support. Here, seven years after the last global assessment of research priorities, we conducted a priority-setting exercise to identify persistent knowledge and implementation gaps, and the strategic priorities that must be addressed to enable scalable, high-integrity and equitable management of blue carbon ecosystems in a rapidly evolving policy and finance landscape. The highest priority focuses on managing blue carbon ecosystems to support coastal communities while integrating traditional ecological knowledge, emphasizing the essential role of social legitimacy and equity in enabling scalable, long-lasting outcomes. Additional priorities focus on developing cost-effective restoration methods, improving the accuracy of greenhouse gas flux estimates, quantifying the impacts of human activities on carbon cycling and integrating co-benefits such as biodiversity and coastal protection into natural capital frameworks. Emerging technologies like remote sensing, machine learning and data-sharing platforms are also highlighted as transformative tools to fill knowledge gaps and scale solutions. Collectively, these priorities highlight the complexity of blue carbon science and the need for inclusive interdisciplinary approaches that support the resilience and livelihoods of coastal communities.

Seagrass ecosystems are pivotal contributors to coastal carbon sequestration through the long-term burial of organic carbon (OC) in sediments. Yet global burial estimates remain uncertain, with early values of 138 ± 38 g OC m-2 yr-1 derived from a limited dataset biased toward highly depositional communities and indirect, production-based approaches. We call for a downward revision, supported by a data-driven assessment based on a global synthesis of 326 dated sediment cores integrating OC burial over the last century. We find that seagrass meadows bury OC at a geometric mean rate of 26 ± 2 g OC m-2 yr-1, with an area-weighted global average of 33 ± 10 g OC m-2 yr-1 accounting for bioregional differences in seagrass distribution. Globally, these rates scale to 6–16 Tg C yr-1, based on current mapped seagrass extent (247,800–366,200 km2), and reveal that ~15% of seagrass net community production is retained and buried locally. Although our estimate is roughly one-fourth of earlier values, seagrass sediments still account for 3–6% of total oceanic OC burial, despite occupying <0.1% of the seafloor. Combined with mangroves and tidal marshes, OC burial in vegetated coastal sediments represents an estimated 8–13% of total oceanic OC burial.

Seagrass meadows play a key role in the global carbon cycle through storing carbon in their biomass and soils. However, the lack of global assessments of carbon stocks in seagrass biomass and net primary production (NPP) limits our understanding of their role in the carbon cycle. Here, we provide global estimates of biomass carbon stocks and NPP encompassing seagrasses with different life-history strategies, across bioregions and 66 countries. Seagrass meadows show up to 800-fold differences in biomass across different life-history strategies and bioregions (mean ± SE; 1551 ± 40 kg C ha⁻¹), whereas seagrass NPP (5833 ± 557 kg C ha⁻¹ yr⁻¹) ranks among the highest within photosynthetic ecosystems. We estimate seagrass biomass carbon stocks at 24–40 Tg C and NPP at 83–137 Tg C yr⁻¹ within 160,387 to 266,500 km² of global seagrass extent. This study showcases the role of seagrasses in the global carbon cycle and provides the basis for their inclusion in carbon crediting schemes towards implementing conservation actions for climate change mitigation.

Mangrove planting has been employed for decades to achieve aims associated with restoration and afforestation. Often, survival of planted mangroves is low. Improving survival might be aided by augmenting the understanding of which planting methods and environmental variables most influence plant survival across a range of contexts. The aim of this study was to provide a global synthesis of the influence of planting methods and background environment on mangrove survival. This was achieved through a global meta-analysis, which compiled published survival rates for the period 1979–2021 and analyzed the influence of decisions about minimum spacing and which life stage to plant, and environmental contexts such as climate, tidal range and coastal setting on the reported survival of planted individuals, classified by species and root morphology. Generalized Additive Mixed Modeling (GAMM) revealed that planting larger mangrove saplings was associated with increased survival for pencil-rooted species such as Avicennia spp. and Sonneratia spp. (17% increase cf. seedlings), while greater plant spacing was associated with higher survival of stilt-rooted species in the family Rhizophoraceae (39% increase when doubling plant spacing from 1.5 to 3.0 m). Tidal range showed a nonlinear positive correlation with survival for pencil-rooted species, and the coastal environmental setting was associated with significant variation in survival for both pencil- and stilt-rooted species. The results suggest that improving decisions about which species to plant in different contexts, and intensive care after planting, is likely to improve the survival of planted mangroves.

Policies aiming to preserve vegetated coastal ecosystems (VCE; tidal marshes, mangroves and seagrasses) to mitigate greenhouse gas emissions require national assessments of blue carbon resources. Here, we present organic carbon (C) storage in VCE across Australian climate regions and estimate potential annual CO₂ emission benefits of VCE conservation and restoration. Australia contributes 5–11% of the C stored in VCE globally (70–185 Tg C in aboveground biomass, and 1,055–1,540 Tg C in the upper 1 m of soils). Potential CO₂ emissions from current VCE losses are estimated at 2.1–3.1 Tg CO₂-e yr^-1, increasing annual CO₂ emissions from land use change in Australia by 12–21%. This assessment, the most comprehensive for any nation to-date, demonstrates the potential of conservation and restoration of VCE to underpin national policy development for reducing greenhouse gas emissions.

We report severe bleaching in a turbid water coral community in north-western Australia. Towed still imagery was used for a benthic survey near Onslow in March 2013 to assess thermal stress in hard and soft corals, finding 51–68% of all corals fully bleached in 10–15-m water depth. Tabulate or foliaceous Turbinaria was the locally most abundant hard coral (46%), followed by massives such as faviids and poritids (25%) and encrusting coral (12%), thus over 80% of the local corals could be considered to be bleaching resistant. All coral groups were bleached in similar proportions (massive hard corals 51% < soft corals 60% < encrusting hard corals 62% < Turbinaria 62% < ‘others’ 68%). NOAA data and environmental assessments suggest previous recurrent thermal stress throughout the last 10 years in the study area. On the basis of these records this stress apparently changed the community structure from bleaching vulnerable species such as Acropora, leaving more tolerant species, and reduced coral cover. We could see no evidence for adaptation or acclimation of corals in this area. Towed still imagery was found to be a suitable means for rapid and large-scale bleaching studies in shallow, turbid areas where diving can be difficult or impossible.

TheMediterranean coralligenous substratum is a hard bottom of biogenic origin, mainly composed of calcareous algae, growing in dim light conditions. Sponges are among of the most representative taxa of the coralligenous assemblages, with more than 300 recorded species of different habits: massive, erect, boring and insinuating. When sponges die, their siliceous spicules remain trapped in the biogenic concretion, offering the opportunity to describe the coralligenous spongofauna over a very long span of time, virtually dating back to a large part of theHolocene period. The data reported here were obtained from core samples collected from four coralligenous concretions. Each block was collected in a different locality of theLigurianSea:SantoStefanoShoals,Bogliasco,Punta delFaro (PortofinoPromontory) andPuntaManara.Radiocarbon age determinations indicate for these conglomerates a maximal age between 1600 and 3100 years. The spicules trapped in the cores show deep dissolution marks in the form of circular holes on their surface or present an enlargement of the axial canal. However, their original shape, generally intact, suggests the absence of mechanical injuries and allows a tentative identification at the species level. The analysis of these old spicules reveals an ancient sponge assemblage composed of 30 recognisable species. This indicates that almost one half of the sponge community today settled on coralligenous substrata has been present in the conglomerates for their entire existence.