CR2025_50 Marine Forests in Flux: The Impact of Climate Change on Seaweed Carbon Sequestration

Lead Supervisor: John Griffin, Department of Biosciences, Swansea University

Email: j.n.griffin@swansea.ac.uk

Co-supervisors: Chris Yesson, Zoological Society of London; Sarah Wakelin, National Oceanography Centre; Karen Robinson, Natural Resources Wales

Join an exciting, interdisciplinary PhD project designed to push the boundaries of our understanding of blue carbon in marine ecosystems and contribute to cutting-edge marine science. This project will explore the role of kelp and rockweed forests as dynamic carbon reservoirs, bringing together field research, computational modelling, and machine learning to answer critical questions about how these valuable ecosystems both influence and are impacted by climate change.

Marine forests are known for their productivity and ecological importance^1,2,3. Yet, unlike terrestrial forests, these underwater ecosystems store carbon not by direct accumulation but by transferring it elsewhere through detrital pathways. While often overlooked, recent advances in numerical modelling suggest that this carbon may reach long-term sinks in deep ocean waters, making marine forests an undervalued but potentially essential blue carbon resource^4-6. However, climate change is reshaping temperate marine ecosystems, with warm-affinity seaweed species expanding poleward⁷. These species often degrade more quickly, which could undermine the long-term sequestration potential of marine forests. By examining the effects of species composition and traits^8-10 on blue carbon pathways, this project will offer valuable insights into conservation strategies and the implications of climate change for the ecosystem services of marine forests.

Project Aims and Objectives

1. Uncover Variations in Detrital Carbon Contributions Across Species
   The first objective involves extensive field research to quantify detritus production from seaweed beds dominated by cold- and warm-affinity species along the UK coast. Using UAV-mounted multispectral cameras, combined with ground data, you will develop rapid-assessment proxies that assess detrital output on large spatial scales. This innovative approach allows you to generate high-resolution data and obtain an unprecedented view of carbon pathways across different species and environmental conditions.
2. Link Seaweed Traits to Degradation Rates
   By drawing on Swansea University’s world-leading trait datasets, as well as the NERC-funded INTER-TRAITS project, you’ll explore how specific traits (e.g., carbon content, nitrogen, polyphenols) influence degradation rates. This work is fundamental for building predictive models that can be applied globally to assess blue carbon contributions from a wide range of species. You will also have the opportunity to conduct comparative decomposition experiments across temperature gradients by working with coastal field sites in Wales and Northern Spain, which serve as a natural laboratory for testing how warming affects potential carbon storage.
3. Map Detritus Transport with Hydrodynamic Models
   Using hydrodynamic particle tracking, you will model how detrital carbon travels through marine currents, providing a detailed understanding of transport pathways and destinations. By linking findings from field data and trait analysis, this objective will determine the final resting place of seaweed carbon, a crucial element in estimating long-term sequestration potential. You’ll work with state-of-the-art computational resources to undertake oceanographic particle tracking.
4. Predict Future Blue Carbon Potential Under Climate Change
   The final objective integrates AI-driven species distribution modelling to predict how climate change will reshape seaweed forests. AI (machine learning) has proven to efficiently utilise complex sets of environmental factors to reliably predict species distributions, but its application to seaweeds is a frontier. Partnering with Natural Resources Wales, and using extensive data from the ongoing BEF-SCALE project, you’ll harness AI to forecast species shifts and changing detritus dynamics under different climate scenarios, focusing on the coasts of Wales, aligning with the project’s CASE partner. This research will build invaluable insights into how marine forests’ contributions to blue carbon may evolve over the next century.

Please note that alternative approaches can be adopted to ensure inclusivity of applicants for whom extensive fieldwork is not possible. Alternatives such as greater use of satellite remote-sensing and meta-analysis of previous studies, as well as lab-based rather than field-based experimental approaches can be used.

Training opportunities: 

You’ll receive comprehensive, hands-on training in field methods, quantitative ecology, and oceanographic modelling. Initially, you’ll join sampling teams across the UK, Spain, and Portugal as part of ongoing projects, receiving training in practical field methods, including UAV licencing. At Swansea, you’ll also undergo extensive training in advanced statistical analysis and species distribution modelling. At the National Oceanographic Centre in Liverpool, bespoke training will focus on hydrodynamic modelling techniques. You’ll also have the exciting opportunity to conduct fieldwork in the spectacular rias of Northern Spain (with project partners CIIMAR), allowing you to compare decomposition rates along a latitudinal and climatic gradient. 

Student profile: 

This project would be suitable for students with a degree in Biology, Marine Biology, or closely related subject. Relevant experience and/or Masters level qualifications will be an advantage. 

Co-Sponsorship details: 

This project will receive a CASE award from Natural Resources Wales.

References

1. Coleman and Wernberg (2017). Forgotten underwater forests: The key role of fucoids on Australian temperate reefs. Ecology and Evolution. https:/doi.org/1002/ece3.3279
2. Smale et al. (2013). Threats and knowledge gaps for ecosystem services provided by kelp forests: a northeast Atlantic perspective. Ecology and Evolution. https://doi.org/10.1002/ece3.774
3. Fairchild… and Griffin (2024). Topographic heterogeneity triggers complementary cascades that enhance ecosystem multifunctionality. Ecology. https://doi.org/10.1002/ecy.4434
4. Krause-Jensen and Duarte (2016). Substantial role of macroalgae in marine carbon sequestration. Nature Geoscience. https://doi.org/10.1038/ngeo2790
5. Filbee-Dexter et al. (2024). Carbon export from seaweed forests to deep ocean sinks. Nature Geoscience. https://doi.org/10.1038/s41561-024-01449-7
6. Van der Mheen et al. (2024). Substantial kelp detritus exported beyond the continental shelf by dense shelf water transport. Scientific Reports. https://doi.org/10.1038/s41598-023-51003-5
7. Assis et al. (2024). Kelp forest diversity under projected end-of-century climate change. Diversity and Distributions. https://doi.org/10.1111/ddi.13837.
8. Griffin et al. (2009). Functional diversity predicts overyielding effect of species combination on primary productivity. Oikos https://doi.org/10.1111/j.1600-0706.2008.16960.x
9. Mauffrey et al. (2020). Seaweed functional diversity revisited: Confronting traditional groups with quantitative traits. Journal of Ecology. https://doi.org/10.1111/1365-2745.13460
10. Griffin et al. (2024). The untapped potential of categorical traits in seaweed functional diversity research. Journal of Ecology. https://doi.org/10.1111/1365-2745.14178