Dr Thierry Chopin Investing in nature-based actions and seaweed farming: One of the five opportunities to make the Ocean part of the solution to climate change
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n my October column, I reported that we (19 researchers and policy analysts) published the report, The Ocean as a Solution to Climate Change: Five Opportunities for Action, for the High Level Panel for a Sustainable Ocean Economy (HLPSOE). It was endorsed by its 14 serving head of state and government members at the United Nations Secretary-General’s Climate Action Summit in New York, on September 23rd, 2019. Against the backdrop of the speech of Greta Thunberg, the rather bleak picture of the Intergovernmental Panel on Climate Change (IPCC) report on the Ocean and the Cryosphere, and the never ending Trump saga at the UN and domestically, it was not easy to position our more optimistic report. We believe that, through five opportunities for action, the Ocean could be a substantial solution to climate change. It could deliver up to 21 percent (11.82 GtCO2e/ year) of the annual greenhouse gas (GHG) emissions cuts needed by 2050 to keep global temperature rises below 1.5°C. In this column, I will develop one of the opportunities for action that should be of interest to the readers of International Aquafeed and the aquaculture sector.
Investing in nature-based climate solutions
Conserving and restoring coastal and marine ecosystems, including mangroves, salt marshes, seagrass beds and wild seaweed beds, as well as developing seaweed aquaculture, should have significant mitigation impacts. Mangroves, salt marshes, and seagrass beds are highly productive vegetated coastal ecosystems, which are referred to as “blue carbon” ecosystems, analogous to “green carbon” ecosystems on land. They are hotspots for carbon storage, with Table 1: Estimates of mitigation potential from blue carbon ecosystems and seaweed farming Mitigation option Conservation/protection
Restoration/expansion
Description
Mitigation potential by 2050 (GtCO2e/year)
Mangroves
0.02-0.04
Salt marshes
0.04-0.07
Seagrasses
0.19-0.65
Wild seaweed beds
?
Mangroves
0.16-0.25
Salt marshes
0.01-0.03
Seagrasses
0.03-0.05
Wild seaweed beds Mitigation potential from blue ecosystems Expansion of seaweed farming Total mitigation potential
? 0.45-1.09
Seaweed aquaculture
0.05-0.29 0.50-1.38
soil carbon sequestration rates per hectare up to 10 times larger than those of terrestrial ecosystems. Most of their carbon (5090%) is stored within the soil where saltwater inundation slows decomposition of organic matter, leading to the accumulation of extensive soil carbon stocks. When these ecosystems are degraded and converted, carbon in their biomass and soils, which may have accumulated over hundreds or thousands of years, is oxidised and emitted back to the atmosphere in a matter of decades. Thus, protection of blue carbon ecosystems offers an efficient pathway to avoid CO2 emissions, particularly for nations with large areas of coastal vegetation and high rates of loss. For example, conversion of mangroves to aquaculture accounts for 10 to 20 percent of CO2 emissions associated with land-use change in Indonesia. The area covered by blue carbon ecosystems is equivalent to only 1.5 percent of terrestrial forest cover, yet their loss and degradation are equivalent to 8.4 percent of CO2 emissions from terrestrial deforestation because of their high carbon stocks per hectare. The most extensive and productive coastal vegetated ecosystems are formed by seaweeds. Their areal coverage is estimated - though with large uncertainty - to be 3.5 million km2 of coastal regions. Seaweeds lack root structures that would sequester and trap soil carbon, which means that the climate mitigation value of wild seaweed habitats is largely through the export of organic carbon in their biomass to sinks located in shelf sediments and in the deep ocean. There are currently too many knowledge gaps to enable us to provide a robust estimation of the sequestration and mitigation potential of wild seaweed beds (one study puts it in the range of 0.22–0.98 GtCO2e/year).
Estimating the mitigation potential from blue carbon ecosystems and seaweed farming
Three mitigation options can be considered for these coastal and marine ecosystems: • Conservation and protection of blue carbon ecosystems, by halting the loss and degradation of these ecosystems, thus avoiding direct land-use change emissions of carbon that is currently stored in soils and vegetation, and additional emissions from alternative land use, such as agriculture • Restoration and expansion of degraded blue carbon ecosystems, involving rehabilitating the soil and associated organisms and thereby restoring their ability to sequester and store carbon • Expansion of seaweed biomass through aquaculture The potential mitigation contribution from coastal and marine ecosystems is estimated to be between 0.45 and 1.09 GtCO2e/ year by 2050. Due to a lack of data, this estimate does not include the potentially significant mitigation effects associated with the conservation and restoration of wild seaweed beds. Knowledge gaps are currently too large because the extent of lost macroalgal habitats that could be restored is unknown. Moreover, methods and success rates of restoration and protection measures (including sustainable harvest methods) need to be explored and reviewed.
Expansion of seaweed production through aquaculture
Adding seaweed farming to the nature-based solution set could remove an additional 0.05-0.29 GtCO2e/year by 2050, for a total mitigation potential of 0.50-1.38 GtCO2e/year from the conservation, restoration and sustainable management of coastal and marine ecosystems (See Table 1). There are still some uncertainties regarding the rates of expansion of the seaweed farming industry and the proportion of production that would be directly sequestered (through export of dissolved and particulate macroalgal carbon to oceanic sinks during the production phase). Scaling up seaweed production via aquaculture offers different potential mitigation pathways:
14 | November 2019 - International Aquafeed