Seychelles Plateau's oil spill vulnerability.

Small Island Developing States, such as Seychelles, are highly susceptible to oil pollution incidents, with limited infrastructure for detection and mitigation. While an oil spill could significantly impact Seychelle's tourism industry, contributing to ~40% of its GDP, the archipelago's vulnerability remains largely unknown. Here, we developed a high-resolution ocean circulation model for Seychelles Plateau, simulating currents over three years (2018-2020) to model oil spill dispersal to six ecologically and economically significant coastal areas. Our findings reveal distinct seasonality in offshore risk distribution, driven by seasonal fluctuations in atmospheric and oceanic circulations. We show that an oil spill originating from any part of the plateau could potentially impact a sensitive coastal site in less than five days. By identifying high-risk areas, including the major north-south shipping route, we emphasize the importance of close satellite and airborne monitoring for early warnings to protect Seychelles' coastal ecosystems and tourism industry.

Trait-based approaches reveal that deep reef ecosystems in the Western Indian Ocean are functionally distinct.

Tropical deep reefs (>30 m) are biologically and ecologically unique ecosystems with a higher geographic reach to shallow (<30 m) reefs. Yet they are poorly understood and rarely considered in conservation practices. Here, we characterise benthic and fish communities across a depth gradient (10-350 m) in remote coral atolls in Seychelles, Western Indian Ocean. Using taxonomic and trait-based approaches we present the taxonomic and functional composition of shallow and deep reef communities, with distinct communities and traits dominating different depths. Depth-related changes in community metrics (taxa richness, abundance and biomass) and functional diversity metrics (richness, dispersion, and evenness) indicate complex relationships across different biological components (fish, benthos) that differ between shallow and deep reefs. These in turn translate into different patterns of reef resilience against disturbance or species invasions with depth. Notably, deep reefs host on average fewer and less abundant taxa but with higher functional contribution and originality scores, some of which are of conservation concern. Overall, the results highlight the unique nature of deep reefs that requires their explicit consideration in conservation and management activities.

Massive marine methane emissions from near-shore shallow coastal areas.

Methane is the second most important greenhouse gas contributing to climate warming. The open ocean is a minor source of methane to the atmosphere. We report intense methane emissions from the near-shore southern region of the North Sea characterized by the presence of extensive areas with gassy sediments. The average flux intensities (~130 µmol m(-2) d(-1)) are one order of magnitude higher than values characteristic of continental shelves (~30 µmol m(-2) d(-1)) and three orders of magnitude higher than values characteristic of the open ocean (~0.4 µmol m(-2) d(-1)). The high methane concentrations (up to 1,128 nmol L(-1)) that sustain these fluxes are related to the shallow and well-mixed water column that allows an efficient transfer of methane from the seafloor to surface waters. This differs from deeper and stratified seep areas where there is a large decrease of methane between bottom and surface by microbial oxidation or physical transport. Shallow well-mixed continental shelves represent about 33% of the total continental shelf area, so that marine coastal methane emissions are probably under-estimated. Near-shore and shallow seep areas are hot spots of methane emission, and our data also suggest that emissions could increase in response to warming of surface waters.