Abstract
Seaweed aquaculture, the fastest-growing component of global food production, offers a slate of opportunities to mitigate and adapt to climate change. Seaweed farms release carbon that maybe buried in sediments or exported to the deep sea, therefore acting as a CO2 sink. The crop can also be used, in total or in part, for biofuel production, with a potential CO2 mitigation capacity, in terms of avoided emissions from fossil fuels, of about 1500 tons CO2 km-2 year-1. Seaweed aquaculture can also help reduce the emissions from agriculture, by improving soil quality substituting synthetic fertilizer and, when included in cattle fed, lowering methane emissions from cattle. Seaweed aquaculture contributes to climate change adaptation by damping wave energy and protecting shorelines, and by elevating pH and supplying oxygen to the waters, thereby locally reducing the effects of ocean acidification and de-oxygenation. The scope to expand seaweed aquaculture is, however, limited by the availability of suitable areas and competition for suitable areas with other uses, engineering systems capable of coping with rough conditions offshore and an increasing market demand for seaweed products, among other factors. Despite these limitations, seaweed farming practices can be optimized to maximize climate benefits, which may, if economically compensated, improve the income of seaweed farmers.
Highlights
With an annual production of 27.3 million tons in 2014 and a growth rate of 8% year−1, seaweed aquaculture comprises 27% of total marine aquaculture production
We evaluate the role of seaweed aquaculture in adaptation to specific impacts of climate change in the marine environment, such as ocean acidification, deoxygenation, and shoreline erosion (e.g., Gattuso et al, 2015)
We recently summarized 105 reports of sequestration of seaweed to carbon sequestration in sediments or the deep sea, and showed that 25% of the carbon exported from macroalgal stands, which represents about 43% of their net primary production, is sequestered in continental shelf sediments or in the deep-sea (Krause-Jensen and Duarte, 2016)
Summary
With an annual production of 27.3 million tons in 2014 and a growth rate of 8% year−1, seaweed aquaculture comprises 27% of total marine aquaculture production. Providing economic incentives associated with the benefits for climate change mitigation and adaptation may be instrumental in supporting increased seaweed production into the future Seaweed production, both from wild stocks and from aquaculture, represents an important conduit for CO2 removal from the atmosphere, with strongly autotrophic seaweed communities globally taking up 1.5 Pg C year−1 via their netproduction (Krause-Jensen and Duarte, 2016). The potential of managing seaweed production to mitigate climate change by sequestering CO2 has not yet been fully incorporated into the emergent concept of Blue Carbon, referring to climate change mitigation strategies based on the capacity of marine plants to bind CO2 (Nellemann et al, 2009; McLeod et al, 2011; Duarte et al, 2013) The reason for such neglect is the belief that the large majority of seaweed production is decomposed in the ocean and does not represent a net sink for CO2. It is unlikely that seaweed aquaculture will comprise a sizeable fraction of vegetable production on land, as food demand is growing with increasing human population
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