Sea into the future

Interests

There has been a significant oversight in conservation, with extensive soft sediment habitats on continental shelves being largely ignored in the creation of marine protected areas. 

Despite strong evidence supporting an ecosystem-based approach to conservation, priority has often been given to biodiversity “hotspots” and “ecological features.” This focus reduces the areas eligible for protection and helps alleviate conflicts with commercial interests. 

However, a new avenue for protecting the seabed on an unprecedented scale is emerging through carbon offsetting and nature-based climate solutions.

Ironically, the driver for reassessing the importance of soft sediment ecosystems and their protection may not be biodiversity itself. 

Instead, increasing interest in seabed carbon storage and climate mitigation may serve as a means for the ecological significance of continental shelf sediments to gain attention from government policies and economic stakeholders. 

Foresight

The Convex Seascape Survey exemplifies the newfound interest in the ability of continental shelves to store organic carbon. 

Over a five-year mission, the Convex Seascape Survey has aimed to identify areas worldwide to evaluate how seabed organic carbon stocks and the ecological communities that regulate them respond to protection from human activity. 

This endeavor has proven challenging, even with a global scope, highlighting the general neglect of soft sediment environments in marine protection strategies. 

There are a few rare, highly protected areas that include soft sediment habitats. Among the most notable is the South Arran Marine Protected Area, spanning 280 square kilometers off the south coast of the Isle of Arran in western Scotland. 

With foresight and determination, the Community of Arran Seabed Trust (COAST) successfully advocated for various protection measures for the area in 2014, including a nearshore region completely free of bottom-towed gear. 

A recent study from the Convex Seascape Survey, in collaboration with COAST, details how sediment organic carbon stocks in the South Arran Marine Protected Area have responded to a range of protection measures alongside diverse ecological communities on and within the seabed. 

Succession

Known collectively as infauna, creatures like polychaete worms and bivalves inhabit the sediment, constantly reworking it as they search for food and create burrows in a process called bioturbation. 

This activity can lead to the long-term burial of organic carbon deeper into the seabed. The study also examined animals living on the sediment surface, known as epifauna, including sponges, soft corals, and more mobile animals like brittle stars, which also play crucial roles in managing carbon flow in the seabed. 

The study showed a notable response to protection. Infauna communities experienced a threefold increase in abundance and a twofold rise in species diversity, while sediment organic carbon content also increased after adjusting for mud content. 

While this aligns with the recognized narrative of biodiversity recovery in well-managed marine protected areas, these findings offer something rarer: validation for soft sediment environments, providing insight into how this vast habitat, if allowed to recover, could support significantly higher biodiversity and potentially greater organic carbon content than previously believed.

Even after a decade of protection, this marks the beginning of ecological succession and biodiversity recovery, which is likely to progress more slowly in response to protection compared to other environments. 

Several decades may be needed for the South Arran Marine Protected Area to achieve its full ecological potential, but in doing so, it could help counteract the shifting baseline syndrome that has affected perceptions of the European shelf seabed for over a century. 

Consequences

Soft sediment habitats present a vast opportunity for nature-based climate solutions, incentivizing seabed protection on a scale far beyond what the biodiversity agenda has offered, particularly for soft sediment habitats, which have largely been overlooked. 

As the survey continues to release data from various soft sediment habitats worldwide, it advocates for a comprehensive reassessment of these environments. 

Contrary to being naturally barren and resistant to disturbance, soft sediments may represent one of the largest untapped opportunities for biodiversity recovery, carbon storage, and fisheries enhancement in the marine environment. 

We propose that these biodiversity benefits, once driven by carbon offsetting incentives, will soon be recognized as a core mechanism for carbon capture and storage, rather than just an additional advantage. 

Ultimately, we hope this will lead to a significant reevaluation of soft sediments, positively impacting marine conservation efforts globally. 

This Author

Dr Ben Harris is a marine ecologist based at the University of Exeter.