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Potential negative effects of ocean afforestation on offshore ecosystems

journal contribution
posted on 2023-05-21, 16:03 authored by Philip BoydPhilip Boyd, Lennart BachLennart Bach, Catriona HurdCatriona Hurd, Ellie PaineEllie Paine, Raven, JA, Tamsitt, V
Our scientific understanding of climate change makes clear the necessity for both emission reduction and carbon dioxide removal (CDR). The ocean with its large surface area, great depths and long coastlines is central to developing CDR approaches commensurate with the scale needed to limit warming to below 2 °C. Many proposed marine CDR approaches rely on spatial upscaling along with enhancement and/or acceleration of the rates of naturally occurring processes. One such approach is ‘ocean afforestation’, which involves offshore transport and concurrent growth of nearshore macroalgae (seaweed), followed by their export into the deep ocean. The purposeful occupation for months of open ocean waters by macroalgae, which do not naturally occur there, will probably affect offshore ecosystems through a range of biological threats, including altered ocean chemistry and changed microbial physiology and ecology. Here, we present model simulations of ocean afforestation and link these to lessons from other examples of offshore dispersal, including rafting plastic debris, and discuss the ramifications for offshore ecosystems. We explore what additional metrics are required to assess the ecological implications of this proposed CDR. In our opinion, these ecological metrics must have equal weight to CDR capacity in the development of initial trials, pilot studies and potential licensing.


Australian Research Council


Publication title

Nature Ecology and Evolution










Institute for Marine and Antarctic Studies


Nature Publishing Group

Place of publication

United Kingdom

Rights statement

© Springer Nature Limited 2022.

Repository Status

  • Restricted

Socio-economic Objectives

Assessment and management of pelagic marine ecosystems

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