Belize Blue Carbon: Establishing a national carbon stock estimate for mangrove ecosystems.

Mangrove ecosystems are among the most economically and ecologically valuable marine environments in the world. Mangroves are effective at long-term carbon storage within their sediments and are estimated to hold 12 billion metric tons of carbon worldwide. These ecosystems are therefore vitally important for carbon sequestration and, by extension, climate change mitigation. As part of the Paris Agreement, participating countries agree to provide plans to reduce their carbon emissions, or nationally determined contributions (NDCs). However, despite mangroves being recognized as important nature-based solutions, many countries still lack national data on carbon stocks and must use global or regional averages, which may not be sufficiently accurate. Here, we present the national carbon stock estimate of mangrove ecosystems for the NDC of Belize, acquired through a collaborative approach involving government agencies and NGOs. We conducted a comprehensive sampling of mangroves across the country, including a range of mangrove ecotypes. The mean total ecosystem carbon stock (TECS) for the nation was 444.1 ± 21.0 Mg C ha-1, with 74.4 ± 6.2 Mg C ha-1 in biomass stocks, and 369.7 ± 17.7 Mg C ha-1 in sediment stocks. Combining these data with a recent mapping effort, we provide the first national comprehensive mangrove carbon stock estimate of 25.7 Tg C. The national mean from this study varies from previous global analyses, which can under- or overestimate TECS by as much as 0.6 Tg C and 16.5 Tg C, respectively, depending on the study. These data supported the NDC update of Belize, and can be used to inform the country's mangrove protection and restoration commitments. The collaborative approach of this work should serve as a blueprint for other countries seeking to conserve natural blue carbon sinks as a strategy to achieve their climate targets.

Lack of genetic differentiation in yellowfin tuna has conservation implications in the Eastern Pacific Ocean.

Yellowfin tuna, Thunnus albacares, is an important global fishery and of particular importance in the Eastern Pacific Ocean (EPO). According to the 2019 Inter-American Tropical Tuna Commission (IATTC) assessment, yellowfin tuna within the EPO is a single stock, and is being managed as one stock. However, previous studies indicate site fidelity, or limited home ranges, of yellowfin tuna which suggests the potential for multiple yellowfin tuna stocks within the EPO, which was supported by a population genetic study using microsatellites. If numerous stocks are present, management at the wrong spatial scales could cause the loss of minor yellowfin tuna populations in the EPO. In this study we used double digestion RADseq to assess the genetic structure of yellowfin tuna in the EPO. A total of 164 yellowfin tuna from Cabo San Lucas, México, and the Galápagos Islands and Santa Elena, Ecuador, were analysed using 18,011 single nucleotide polymorphisms. Limited genetic differentiation (FST = 0.00058-0.00328) observed among the sampling locations (México, Ecuador, Peru, and within Ecuador) is consistent with presence of a single yellowfin tuna population within the EPO. Our findings are consistent with the IATTC assessment and provide further evidence of the need for transboundary cooperation for the successful management of this important fishery throughout the EPO.