Restorative aquaculture projects in Southwest England 

The latest edition of our membership magazine, The Marine Biologist celebrates the United Nations Decade on Ecosystem Restoration 2021–2030. Restorative aquaculture can have benefits for both humans and the environment, and here we present a brief summary of two sea farming projects in Southwest England illustrating intentional cultivation of seaweed and mussels.

1. Sustainable seaweed aquaculture

The Marine Biological Association’s Cat Wilding is our Senior Project Officer on a collaborative project with the University of Exeter, Plymouth Marine Laboratory, Cornish Seaweed Company, Westcountry Mussels of Fowey, and Hortimare to help establish environmentally and commercially sustainable seaweed aquaculture, with support from the European Maritime and Fisheries Fund.

Seconnd year kelp growth (March 2020). Image credit Cat Wilding.

Although well established in Asia, seaweed aquaculture in the UK is still an emerging field, requiring optimisation of techniques and technologies to facilitate commercial scale production. The project team are cultivating local kelp species, including the sugar kelp Saccharina latissima, integrated with mussel aquaculture at a site in South Cornwall. Cat says, “In addition to investigating techniques for optimising yield, such as seeding method and strategy, we are also exploring how kelp aquaculture can benefit biodiversity through creation of habitat, and potentially mitigate harmful algal blooms (HABs), by mopping up excess nutrients. Cultivation of seaweed can also sequester carbon, provide coastal protection, and even supply propagules to restore wild kelp beds that have been damaged by anthropogenic impacts”.

She adds “It’s really exciting to be working on an aquaculture project that has the potential to provide environmental benefits and enhance marine ecosystem services. Following deployment in November 2019 we have a strong crop growing, and I can’t wait to get some results that we anticipate will evidence the positive ecosystem and economic outcomes of seaweed mariculture”.

Cat Wilding examining a kelp holdfast. Image credit Caylon la mantia

The habitat created by cultivated kelp differs from wild kelp forests. Crops are harvested, which prevents a climax community from building up, and cultivation usually works with monospecific stands whereas natural habitats are often characterised by a variety of seaweed species. The structural complexity of the habitat is different too, as farmed kelps form their holdfast around culture lines, and they will be exposed to a different hydrodynamic environment in the water column than on their wild conspecifics growing on the benthos. Nonetheless the potential biodiversity value created by seaweed farms is substantial, as a single kelp plant can support an assemblage of 8,000 individuals across 130 species. The project is also aiming to draw comparisons between the habitat value of cultivated kelp with adjacent wild populations.

Brittlestar. Image credit Cat Wilding.

Integrated multi-trophic aquaculture (IMTA)

Locating seaweed cultivation alongside mussel aquaculture has clear advantages. The waste products of one species are recycled and provide the inputs to culture another, in a truly circular system. Plus, if algal culture is successful in mitigating HABs there is the potential to protect shellfish production. There are practical benefits too, as logistically their cultivation utilises similar infrastructure, and co-location can simplify the aquaculture licensing process.

Nora Salland measuring kelp fronds. Image credit Cat Wilding.

2. Bivalve aquaculture at high-energy sites

Scientists from the University of Plymouth are working with local offshore mussel farmers and scallop ranchers to assess the potential win-win outcomes of bivalve aquaculture at high energy sites. Offshore mussel farmers Offshore Shellfish Ltd first deployed longline ropes in Lyme Bay in 2013 on degraded seabed habitat that was previously dredged and trawled. They are now successfully harvesting mussels Mytilus edulis that naturally settled on the ropes, and feed on plankton in the water.

Using local fishing boats as research platforms, Dr Sheehan’s research group developed innovative cost- and-time effective monitoring approaches to assess how the farm interacts with the surrounding ecosystem. Preliminary results show that the ropes are supporting diverse reef communities in the water column, while on the seabed, mussel clumps that have fallen from the ropes are potentially restoring biogenic reef habitats that once featured in Lyme Bay. Consequently, commercially important reef associated organisms are also increasing in abundance both on the seabed (e.g. crab and lobsters) and in the water column (e.g. horse mackerel), and are attracting local fishers to the mussel farm. Research is now underway to assess the potential spillover effect of these commercial species into neighbouring fishing grounds and marine protected areas using acoustic telemetry ;    

As a result of excluding bottom towed fishing and adding structure that promotes food production, offshore bivalve production has the potential to be one of the most sustainable forms of food production, that also benefits other fisheries. Despite this, there is a lack of support for these industries, and so it is imperative that we continue to undertake robust monitoring of new sites to inform best practice and encourage the sustainable development of these new emerging blue industries.

Dr Emma Sheehan

May 1, 2020 By guba