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Seaweed harvesting

Wild seaweed is a useful resource that can be harvested sustainably – but its sustainable management can be a complex task.

There is growing interest in using Scotland’s rich wild seaweed resources in a number of industries. Commercial wild seaweed harvesting can range in scale from a few kilos of hand-harvested seaweed to thousands of tonnes of kelp harvested mechanically.

The Scottish Government is considering the need for future regulation of commercial wild seaweed harvesting. Scottish Natural Heritage provides advice on seaweed harvesting activities that take place in or next to protected areas.

Marine Biopolymers LTD - Mechanical kelp harvesting, west coast of Scotland - scoping report - SNH comments

We were asked to provide advice to Marine Scotland to inform a scoping opinion of Marine Biopolymers' proposal for large scale mechanical kelp harvesting. As it is currently written, we are unable to provide this advice. Kelp plays a vital role in providing habitats for juvenile fish, protecting coasts from erosion, and carbon storage. The report does not currently provide enough detail for us to advise on how to assess the environmental impacts of the proposal on this important marine habitat.

Our full response to Marine Scotland suggests that the proposal could be re-worked to incorporate a phased approach to harvesting, where impacts are monitored and addressed in a smaller area before plans are scaled-up. We explain what information we need to provide our advice, for example the specific locations in which they plan to harvest and how they will monitor for any disturbance to habitats and wildlife. If Marine Biopolymers were to redraft their proposal, we would revisit the subject and make a recommendation then.

Seaweed functions

Seaweed plays an important role in coastal and marine ecosystems. Kelp forests are one of the most productive and dynamic ecosystems on Earth, with kelps often described as ‘ecosystem engineers’, as they’re key habitat-forming species.

Seaweeds are a valuable food source for all sorts of animals, both directly and indirectly. Some graze on seaweed itself, while others feed on the organic matter that seaweeds release into coastal waters.

Seaweeds are also habitats for animals and other marine plants. Kelp forests have been found to provide nursery grounds for commercial fish and shellfish as well as food resources for seabirds.

Large kelp forests (e.g. west of the Outer Hebrides) can protect our coasts from storm damage by reducing the wave energy reaching land.

Seaweed communities are so important they’re often listed as protected features within designated sites.

Sustainable management

Seaweeds can be harvested sustainably, but harvesting operations must take into account the role of seaweeds as habitats, natural coastal defences and nursery grounds as well as their complex life histories.

Outcomes of harvesting that may affect the marine and coastal environment may include:

  • damage to growing areas of individual plants – can affect regeneration and biodiversity of species that live in and on seaweed
  • loss of seaweed as a habitat used by marine animals and plants
  • opportunistic seaweeds outcompeting those that are harvested

Commercial harvesting

Commercial wild seaweed harvesting is having a revival in Scotland.

Seaweeds are harvested for their alginates. These are used in foods, textiles and pharmaceuticals. There is also some commercial use of seaweeds – mainly egg wrack (Ascophyllum nodosum) – as organic fertilisers.

Seaweed has been in increasing demand by small food and cosmetic businesses in recent years. Interest in evaluating the large-scale harvesting of seaweed in Scotland for use as a biofuel is also growing.

Hand cutting is the most common method of harvesting. Some mechanical cutting takes place and the use of this method is expected to increase as large-scale harvesting proposals go ahead.