The empirical evidence for the social-ecological impacts of seaweed farming

Abstract

Seaweed farming is widely expected to transform the way we approach sustainable developments, particularly in the context of the ‘Blue Economy’. However, many claims of the social and ecological benefits from seaweed farming have limited or contextually weak empirical grounding. Here we systematically review relevant publications across four languages to form a comprehensive picture of observed—rather than theorised—social and environmental impacts of seaweed farming globally. We show that, while some impacts such as improved water quality and coastal livelihoods are consistently reported, other promulgated benefits vary across cultivation contexts or are empirically unsubstantiated. For some communities, increasing dependence on seaweed farming may improve or worsen the cultural fabric and their vulnerability to economic and environmental shocks. The empirical evidence for the impacts of seaweed farming is also restricted geographically, mainly to East Asia and South-East Asia, and taxonomically. Seaweed farming holds strong potential to contribute to sustainability objectives, but the social and ecological risks associated with scaling up global production remain only superficially understood. These risks require greater attention to ensure just, equitable, and sustainable seaweed industries can be realised.

Climate benefits of seaweed farming: estimating regional carbon emission and sequestration pathways

“…While our goal was to assess the potential climate benefits of kelp aquaculture in BC, its feasibility will also need to consider a number of societal, economic, and ecological questions. Seaweed aquaculture has often been shown to provide sustainable economic livelihoods and contribute to community well-being, however this is dependent on local and regional conditions [42,55,56] . In BC, seaweed aquaculture expansion would likely require development in remote coastal communities (e.g., transport costs may incentivise pre-processing such as drying to be done close to where kelp is harvested), many of which are within the territories of Indigenous people and governments.…”

“…Similarly, the potential positive and negative ecological effects of expansive seaweed aquaculture are myriad. Seaweed aquaculture can improve water quality [60,61] , protect shorelines [4,62] , create refugia from ocean acidification [4,63] , and provide habitat and nutrients to various marine species [61,[64][65][66] , however these benefits will be context species dependent [42] . On the other hand, the large areas required for effective CDR may lead to competition for nutrients and light, reducing productivity of wild seaweeds, phytoplankton, and benthic communities [6,47,67] .…”

“…Recent estimates have suggested that between 48-119 million km 2 of the global ocean (an area 24-60 times the size of Greenland) may be suitable for seaweed production [5,40] , however the industry remains nascent in most countries [5,41] . Farming seaweeds also has other potential benefits including reducing excess anthropogenic nutrients in ocean water, nourishing coastal ecosystems, and reducing wave impacts on shorelines [4,42,43] . As such, there is considerable excitement around seaweed aquaculture and substantial marketing, investment, and media attention focused on the climate and ecosystem benefits of the industry [16,44] .…”

Global estimates of suitable areas for marine algae farming

“…Invasive seaweed cultivation has been shown to cause competition, suffocation, and death of reef-building corals, highlighting the need to avoid introducing non-native species (Edwards 2015, Neilson et al 2018). While some evidence suggests that mariculture of native seaweed has had little to no impact on wild macroalgae populations (Spillias et al 2023), the infrastructure of seaweed farms can provide a unique environment for invasive species to grow (Taormina et al 2018, Barbier et al 2020. In some cases, seaweed farms may inhibit bloomforming microalgae (Yang et al 2015, Jiang et al 2020, but poor management of seaweed farms can facilitate the growth of harmful macro-algae species (Liu et al 2009, 2010, 2013, Zhang et al 2011, 2017, Huo et al 2015, 2016, Spillias et al 2023.…”

Integrating environmental and ecological monitoring with seaweed farming

“…Research on understanding these ecosystem services is beginning to gather pace and a consensus on the roles of carbon and nutrient cycling are beginning to emerge [6], [7]. However, the impacts on marine biodiversity remains a very complex picture, and in the context of the northeast Atlantic region, there are a limited number of comprehensive studies with inconclusive findings that show highly variable observations across different taxa [3], [8].…”