Abstract
Macroalgae form the most extensive and productive benthic marine vegetated habitats globally but their inclusion in Blue Carbon (BC) strategies remains controversial. We review the arguments offered to reject or include macroalgae in the BC framework, and identify the challenges that have precluded macroalgae from being incorporated so far. Evidence that macroalgae support significant carbon burial is compelling. The carbon they supply to sediment stocks in angiosperm BC habitats is already included in current assessments, so that macroalgae are de facto recognized as important donors of BC. The key challenges are (i) documenting macroalgal carbon sequestered beyond BC habitat, (ii) tracing it back to source habitats, and (iii) showing that management actions at the habitat lead to increased sequestration at the sink site. These challenges apply equally to carbon exported from BC coastal habitats. Because of the large carbon sink they support, incorporation of macroalgae into BC accounting and actions is an imperative. This requires a paradigm shift in accounting procedures as well as developing methods to enable the capacity to trace carbon from donor to sink habitats in the ocean.
Highlights
Recognition of the role of vegetated coastal ecosystems as sites of intense carbon (C) sequestration and storage [1,2] led to the development of Blue Carbon (BC) strategies to mitigate and adapt to climate change through the conservation and restoration of these ecosystems [3,4,5]
While most macroalgae grow on rocky shores where sediment accretion does not occur, a significant fraction of macroalgal production is exported [7,8], to eventually reach shelf sediments, including those in angiospermdominated habitats [9,10,11], and the deep ocean, where it can be stored over significant time scales [6]
The first paper was published in 2011 [13], five in 2017, and citations of the BC papers grew 18-fold between 2012 and 2017. This reveals an emerging interest in the topic, including the role of seaweed aquaculture and created seaweed habitats as potential BC resources. This search, did not capture papers published before the term ‘Blue Carbon’ was first introduced [3], such as the seminal 1981 paper by Smith [1], and recent studies discussing the role of macroalgae
Summary
Recognition of the role of vegetated coastal ecosystems as sites of intense carbon (C) sequestration and storage [1,2] led to the development of Blue Carbon (BC) strategies to mitigate and adapt to climate change through the conservation and restoration of these ecosystems [3,4,5]. A potentially large contribution of macroalgae to C sequestration was recently proposed [6]. License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. We evaluate whether macroalgal C fulfils the criteria that have rendered BC a successful strategy to mitigate and adapt to climate change
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