Climate Mitigation through Biological Conservation: Extensive and Valuable Blue Carbon Natural Capital in Tristan da Cunha’s Giant Marine Protected Zone

Abstract

Carbon-rich habitats can provide powerful climate mitigation if meaningful protection is put in place. We attempted to quantify this around the Tristan da Cunha archipelago Marine Protected Area. Its shallows (<1000 m depth) are varied and productive. The 5.4 km2 of kelp stores ~60 tonnes of carbon (tC) and may export ~240 tC into surrounding depths. In deep-waters we analysed seabed data collected from three research cruises, including seabed mapping, camera imagery, seabed oceanography and benthic samples from mini-Agassiz trawl. Rich biological assemblages on seamounts significantly differed to the islands and carbon storage had complex drivers. We estimate ~2.3 million tC are stored in benthic biodiversity of waters <1000 m, which includes >0.22 million tC that can be sequestered (the proportion of the carbon captured that is expected to become buried in sediment or locked away in skeletal tissue for at least 100 years). Much of this carbon is captured by cold-water coral reefs as a mixture of inorganic (largely calcium carbonate) and organic compounds. As part of its 2020 Marine Protection Strategy, these deep-water reef systems are now protected by a full bottom-trawling ban throughout Tristan da Cunha and representative no take areas on its seamounts. This small United Kingdom Overseas Territory’s reef systems represent approximately 0.8 Mt CO2 equivalent sequestered carbon; valued at >£24 Million GBP (at the UN shadow price of carbon). Annual productivity of this protected standing stock generates an estimated £3 million worth of sequestered carbon a year, making it an unrecognized and potentially major component of the economy of small island nations like Tristan da Cunha. Conservation of near intact habitats are expected to provide strong climate and biodiversity returns, which are exemplified by this MPA.

Towards Incorporation of Blue Carbon in Falkland Islands Marine Spatial Planning: A Multi-Tiered Approach

“…Ideally this information can be overlayed with VME and infaunal assemblage mapping, biogeochemistry, and population genetics to estimate blue carbon connectivity from key model sequesters (e.g., corals, sponges and echinoderms). This type of information would validate carbon storage and sequestration estimates based on functional groups at finer temporal and spatial scales (e.g., per population, per area, per year over time) both offshore (e.g., Barnes and Sands, 2017;Barnes et al, 2021) and nearshore (e.g., Morley et al, 2022). However, such estimates also rely on knowledge of a taxon's traits such as feeding strategy, mobility and lifestyle, which is lacking for most benthic taxa (www.SCAR-MarBIN.be).…”

“…A better understanding of these potentially rare and sizable (in terms of area) negative feedbacks on climate change, is valuable in social carbon costs. Seabed biomass shallower than 1000 m in some South Atlantic habitats can accumulate carbon of considerable mitigation potential (Barnes et al, 2021). The eastern Burdwood Bank (adjacent to the NamuncuráMPA), is a proposed MMA, and preliminary research suggests it hosts high carbon storage and sequestration potential (Bax and Cairns, 2014).…”

“…habitats while healthy than to restore once degraded, with compromised carbon storage and sequestration capabilities (Barnes et al, 2021;Bax et al, 2021;Bayley et al, 2021). In the context of blue carbon, understanding key ecosystem information like the location, extent, and condition of broad scale habitat types, will be critical in understanding sequestration pathways and capacity.…”

Depth and latitudinal gradients of diversity in seamount benthic communities

“…OTUs were identified to the highest For these OTUs, values used were either 1% (as most were only present in very small abundances), or between 10% and 100% in 10% increments. The benthic assemblage composition is described in Bridges et al (2021) and blue carbon ecosystem services in Barnes et al (2021).…”

Assessing the carbon sink capacity of coastal mariculture shellfish resources in China from 1981–2020

“…In addition to forest and grassland ecosystems, the importance of carbon sequestration by marine organisms as an ecological carbon sink is becoming increasingly recognized (McKay et al, 2021). Remote islands and seamounts of the United Kingdom's Tristan da Cunha archipelago Marine Protected Zone support substantial biogenic carbon stocks, the conservation of which (and other such carbon-rich natural habitats) can significantly mitigate against climate change (Barnes et al, 2021). Macrophytic algae also sequester more carbon than seagrasses, salt marshes, and mangroves, and play an essential role in marine organic carbon storage (Raven, 2018).…”