Seaweed for fuel and fish

Averil Wilson & Michele Stanley of the Scottish Association for Marine Science (SAMS) discuss how seaweed may potentially be harvested for fuel and as a by-product, provide a natural haven for fish which would no doubt help with the regeneration of stocks.

The need for marine sourced bio-fuels.

As global fossil fuel supplies dwindle and atmospheric carbon concentrations rise, pressure is on to find viable biofuel alternatives to petroleum products. Terrestrial crops such as sugar cane, maize and soya are the predominate biofuel crops grown and their production competes directly for land and water with food production for humans and domestic animals. A potential solution to the global problems associated with growing agricultural crops for biofuels is to cultivate aquatic plants instead. Seaweeds are highly efficient at converting solar energy into biomass, and the productivity of wild stands of large brown seaweeds has been estimated to be in the range of 16-65kg m2 yr-1 as opposed to sugar cane, which is the most productive cultivated terrestrial plant, with a productivity of between 6-18 kg m2 yr-1. Cultivated seaweed is potentially even more productive than wild stands.

The UK has a tradition of utilising storm cast or harvesting wild stands of seaweed from as far back as 600AD. Initially exploited as a food source, seaweed quickly became a valuable fertilizer for agricultural land, and in more recent times its value has been recognised in the chemicals it contains, as a source of iodine and in the production of alginates. Its value as a potential source of biofuel is now being investigated by researchers at the Scottish Association for Marine Science, Oban through the Interreg IVA, Highlands and Islands Enterprise and Crown Estates funded Biomara project (

Farming seaweed.

The scale of production required to meet the demand for biofuel precludes the use of wild grown seaweed as the quantity of seaweed to be harvested from natural sources would be unsustainable, and so if the potential of the seaweed biofuel industry is to be met, seaweed farms will need to provide the raw material. Currently over 100 species are used for food, in medicine, or as fertiliser and in the processing of phycolloids and chemicals with China, the world leader in seaweed cultivation. Here seaweed farms are so large they are visible from space with the seaweed Laminaria japonica being the world’s largest single aquaculture crop. With the European Parliament calling for 10% of road transport fuel to come from renewable sources by 2020, the pressure is on to meet this target and governments across Europe are increasingly turning to marine renewable energy sources. Our marine environment is already under considerable strain, so the deployment of marine renewable devices and the creation of seaweed farms would be expected to add to the pressure these ecosystems are experiencing.

Environmental benefits of seaweed farms.

It is widely recognised that fish tend aggregate around underwater structures and pelagic fish are known to be strongly attracted to floating structures in the pelagic environment. This includes the cages of fin-fish farms. They can provide shelter and act as a refuge for the wild fish from predators and fishing vessels. The feed not eaten by the caged fish passing through the cage nets can provide a source of food for the wild fish below. Wild fish that gather at fish farms tend to be large adults and are in better body condition than their wild counterparts elsewhere in the sea, which in turn may result in better spawning.

There is already good evidence that mature kelp forests provide a valuable refuge for fish, with the structure of the kelp holdfast providing a diverse and sheltered habitat for many species of small fish. These studies suggest that seaweed farms may attract and protect fish and potentially benefit local fisheries. Studies on the impacts of seaweed farms located of the African coast found local fishery catches to be 3-7 times higher in the vicinity of the seaweed farm and concluded this was because the farm acted as a refuge for the fish and as a source of food. It has also been argued by some that seaweed farms can be beneficial to the marine environment if placed near fin-fish farms, as a means of moderating the effects of excess nutrients introduced into the system as a result of fish farm operations.

The predominate seaweed to be cultured in a seaweed farm in the UK would be a species of kelp, a large brown type of seaweed. In wild conditions kelp forests form a natural monoculture, with L. digitata and L. hyperborea forming extended monospecific kelp beds, or kelp forests, which would be comparable to a kelp seaweed farm.

Kelp forests have been shown to provide important nursery and refuge grounds for juvenile gadoids and salmon.

Due to the rich fauna of mobile invertebrates associated with kelp, this habitat is also an important resource for predatory fish and birds. As the natural growth conditions of kelp forests have parallel properties to that of a kelp seaweed farm, the environmental benefits would be similar. In addition to this seaweed farms would also create ‘no-catch’ zones, and so further increasing the value of the refuge for fish. There will be farm management issues to be addressed in regard to harvesting the crop and the impacts that a “clear fell” approach may have on the marine fauna colonising the farm. Overall there is potential here for seaweed farms to provide not only a source of biomass for biofuel, but also to act as a refuge and food source for fish, and so may have a beneficial impact on the marine environment.

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Averil Wilson is an ecologist with resarch interests in coastal zone management, aquaculture and marine renewables. Currently the Biomara Project Co-ordinator, Averil represents SAMS on the Scottish Coastal Forum Steering Group.

Michele Stanley is a marine phycologist and is currently the lead scientist for the Biomara project. Michele’s research interests include marine biochemistry and molecular biology, she has recently been appointed Director of the NERC Algal Bioenergy Special Interest Group.

See here if you’d like to read a little more on the use of seaweed through the ages.

Photos copyright Biomara and Fastily/Gallery

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