Aquaculture and marine ecosystems: Friend or foe?

The Skimmer on Marine Ecosystems and Management

Aquaculture production is an increasingly important component of global seafood production. Seafood production from aquaculture has expanded nearly six-fold since 1990, while capture fisheries production has remained relatively stagnant. According to the UN Food and Agricultural Organization’s most recent analysis of global fisheries and aquaculture, seafood production from aquaculture (excluding seaweeds) exceeded production from marine capture fisheries for the first time in 2016.[i]

Aquaculture’s reputation is mixed, however. It obviously has the potential to feed many people, but it has is associated with a number of observed and potential negative environmental impacts, including:

  • Altering and destroying habitat, such as mangrove forests, for aquaculture facilities
  • Escapes of farmed species into the wild, enabling species invasions and altering the genetics of wild populations
  • Spreading diseases and parasites to wild populations
  • Releasing fecal waste, uneaten food, and pesticides into the local environment, decreasing water quality
  • Contributing to the overfishing of wild fish populations because of the use of wild fish to feed farmed fish.

This negative view obscures the incredible diversity of aquaculture types and their diverse interactions with marine environments. Aquaculture enterprises vary in:

  • What species are cultivated (e.g., seaweeds, mollusks, crustaceans, finfish) and what they feed on (e.g., whether they are photosynthesizers, filter feeders, deposit feeders, herbivores, carnivores)
  • How intense production is (e.g., total biomass per cage, the degree to which fertilizer and supplementary feeds are used)
  • The type of environment production takes place in (e.g., freshwater streams or lakes, fully enclosed tanks, ponds, intertidal, sheltered bays, open ocean, sea pens, ponds, tanks).

Careful siting and management of aquaculture facilities can avoid many of the negative impacts listed above, and new research is calling attention to how many types of aquaculture (particularly that of primary producers and filter and deposit feeders) can provide conservation benefits (e.g., serving as de facto marine protected areas and alleviating wild harvest through replacement or supplementation) and a range of other ecosystem services (e.g., providing habitat, removing excess nutrients in the water column, attenuating wave energy, and sequestering and storing carbon).

In this issue we feature five areas where aquaculture’s interactions with marine ecosystems (and/or our understanding of them) are evolving. We interviewed experts about recent research and developments related to:

We also speak with a biotechnology researcher about the current status of “cellular aquaculture” – the cultivation of seafood tissue in a laboratory or factory environment rather than in an aquatic environment.


Rebecca Gentry: Marine aquaculture can remove nutrients

Editor’s note: Rebecca Gentry is a postdoctoral researcher in the Department of Geography at Florida State University. Her research focuses on spatial ecological and socioeconomic questions related to marine aquaculture development.

The Skimmer: In a recent paper, you reviewed research on a variety of ecosystem services that marine aquaculture can provide in addition to fulfilling its principal commercial objectives of providing food, pharmaceuticals, and other products. These additional ecosystem services include augmenting wild fisheries catches, sequestering carbon, regulating ocean acidification, protecting coastlines, removing nutrients from the water, improving water clarity, and providing artificial habitat. For which of these services is there the strongest evidence right now, and what types of aquaculture provide those services?

Gentry: In our research we found nutrient removal to be the most thoroughly documented ecosystem service provided by marine aquaculture (aside from directly producing food and other materials). This ecosystem service has been widely studied using a range of techniques, including laboratory studies, modeling exercises, and direct measurement of nutrient removal. Algae and bivalves (e.g., clams and mussels) are the most commonly studied species with regard to nutrient removal. But we found that there is evidence for nutrient removal for a range of other species, such as polychaetes and sea cucumbers. Although the potential for nutrient removal is promising, it is important to remember that many types of marine aquaculture (such as most types of finfish farming) add nutrients to the environment and that even some species that are noted for their nutrient removal ability (e.g., bivalves) can also release nutrients into the water column. Understanding that different species interact with the environment in a variety of ways can help inform marine aquaculture development that maximizes ecosystem service benefits and minimizes negative environmental impacts.

The Skimmer: If aquaculture can provide these other ecosystem services, it would be optimal for ocean planning to begin to incorporate consideration of them when siting aquaculture. Are there currently any examples of entities siting aquaculture in ways that maximize other ecosystem services?

Gentry: There are certainly places, such as Jamaica Bay in New York, that are using restorative aquaculture techniques (e.g., aquaculture methods used to promote ecosystem health) to harness the water quality, substrate stabilizing, and habitat provisioning services provided by shellfish. There is also continued interest in integrated multi-trophic aquaculture (IMTA), the co-locating of farms of different species together so that the wastes from one type of farming can be assimilated by other species (e.g., the culturing of finfish, mussels, and seaweed together). [Editor’s note: Read more about IMTA here.] There are IMTA farms in places ranging from Sanggou Bay, China, to pilot projects in the Bay of Fundy, Canada. Most marine spatial planning for marine aquaculture that I am aware of has focused on avoiding the negative effects of marine aquaculture development, but I think that future planning would benefit from integrating the ecosystem services from aquaculture into the process. One example of the types of analyses needed to do this include a 2014 project that mapped locations in the Maryland state waters of the Chesapeake Bay where shellfish aquaculture could contribute to water quality goals and coastal zone enhancement.

 

Hot off the presses: Global analysis of locations for restorative aquaculture

A paper published in October 2019 provides a global analysis of locations where shellfish and seaweed aquaculture have the greatest potential to restore coastal ecosystems and provide benefits to people. Researchers found the greatest opportunities for restorative shellfish aquaculture in Oceania, North America, and Asia, and the greatest opportunities for seaweed aquaculture distributed throughout Europe, Asia, Oceania, and North and South America. View the map.


Gesche Krause: Siting aquaculture offshore can reduce environmental impacts and stakeholder conflicts

Editor’s note: Gesche Krause is a social scientist at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Researcher in Germany. Her research focuses on the social dimensions of marine resource use and social and economic dimensions of sustainable aquaculture.

The Skimmer: Can you tell us a little bit about the status of offshore aquaculture right now?

Krause: As the global population increases, the growing demand for seafood and stagnating supply from capture fisheries creates pressure on aquaculture to fill this gap. Aquaculture production has grown at an average rate of more than 6% annually over the past decade, and today, aquaculture supplies over half of the seafood consumed globally. Further expansion of aquaculture in nearshore environments is difficult, however. Coastal populations and maritime uses have soared in abundance and intensity over the past few decades, and there is tremendous competition for marine space. In Europe, this has created scope to research radical new ways of using marine space efficiently, such as the recently completed EU-funded Multi-Use in European Seas (MUSES) project.

As a result of this new thinking, offshore aquaculture is gaining prominence. Situating aquaculture farther offshore can reduce both the environmental impacts on and the environmental impacts from aquaculture (e.g., nutrient input from terrestrial systems and nutrient effluents from aquaculture) as well as reduce stakeholder conflicts. Moving aquaculture offshore may also enable the large-scale growth in the aquaculture sector necessary to enhance food security for a growing world population.

Several industrialized countries – including China, South Korea, and Norway – are rapidly developing futuristic open ocean finfish systems.[ii] For instance, in Norway, the government granted production licenses, known as “development licenses”, to companies that committed themselves to developing prototypes of installations for offshore salmon (Salmo salar) aquaculture. Once the prototypes are developed, the companies can convert the development licenses to ordinary production licenses. Two of these prototypes are now in operation. Although these prototypes are located within national waters, they are designed to withstand the forces of exposed locations farther offshore (see Figure 1).

In addition to salmon, other offshore farms grow yellowtail (Seriola rivoliana) in the open ocean off Kona, Hawaii, and Bahia de La Paz, Mexico, and seabream (Sparus aurata) off the coast of Ashdod, Israel, in the Mediterranean Sea. Commercial mussel farming currently exists in offshore waters in several countries – Ireland, Scotland, Germany, Belgium, the Netherlands, France, the US, Canada, Japan, China, and New Zealand. All of these farms are in waters with medium to high primary productivity that is favorable to growing mussels.

The Skimmer: What are the major benefits and challenges of offshore aquaculture versus more traditional coastal aquaculture, including benefits or challenges related to marine ecosystem health?

Krause: Moving offshore makes large tracts of relatively uncontested space available for aquaculture. From a production perspective, offshore aquaculture locations can be favorable because they often have higher flushing rates and an absence of parasites. These factors minimize opportunities for disease and parasite transmission and can enable faster growth rates of extractive species (e.g., mussels) and higher yields. This supports efficiency of production and reduces environmental impacts on other locations.

Offshore aquaculture also presents substantial challenges, however. Harsh, high energy offshore environments require new engineering concepts and new farming approaches to maximize the potential for sustainable production and give potential investors in the industry the confidence to invest. Offshore aquaculture also requires clear and secure legal frameworks to avoid “sea grabbing” and the unregulated urbanization of ocean space. Currently, in many countries there is no clear regulation of potential offshore cultivation candidates and/or the application process for starting an offshore aquaculture production enterprise is unclear and complicated. While nearshore aquaculture primarily creates scope for local jobs and incomes, offshore aquaculture in the globalized economy could create benefit for regions or nations other than the nations that hold the rights to the exclusive economic zones (EEZs) where operations are taking place. This holds the potential to shift power relations and create ambiguities about who benefits from use of the ocean commons.

Another consideration for offshore aquaculture is that it may be economically advantageous to design offshore aquaculture installations as multiple-purpose systems, especially when it comes to aquaculture planned in an integrated multi-trophic aquaculture (IMTA) framework. [Editor’s note: Read more about IMTA here.] This will allow aquaculture to capitalize on new as well as existing offshore infrastructure (e.g., wind farms, decommissioned offshore oil platforms) and save on construction and operation costs. However, the integrated farming of vastly different organisms with different needs in an IMTA system is complex at best.

It is also important to note that less than 40% of aquaculture today is of an intensive nature. As crops increase in value, however, lower-intensity systems are likely to be updated and could be converted to IMTA systems. The Green Aquaculture Intensification (GAIN) project in Europe is currently conducting research on circular economy approaches to aquaculture and how it can be intensified in an ecologically sustainable manner.


Thierry Chopin: Integrated multi-trophic aquaculture (IMTA): an ecosystem-based approach to aquaculture

Editor’s note: Thierry Chopin is a professor of marine biology and director of the Seaweed and Integrated Multi-Trophic Aquaculture Research Laboratory at the University of New Brunswick in Canada. He is also president of Chopin Coastal Health Solutions Inc. His research focuses on the ecophysiology/biochemistry/cultivation of seaweeds and the development of IMTA for environmental sustainability, economic stability, and societal acceptability.

[The responses below are excerpted from a longer interview with Thierry Chopin. Read the full interview.]

The Skimmer: Can you tell us a little bit about what IMTA is?

Chopin: With IMTA, farmers cultivate species from different trophic levels and with complementary ecosystem functions in proximity. They combine fed species (e.g., finfish that need to be provided with feed) with extractive species (e.g., seaweeds, aquatic plants, shellfish, and other invertebrates that extract their food from the environment) to take advantage of synergistic interactions among them. In these systems, biomitigation operates as part of a circular economy (i.e., nutrients are no longer considered wastes or by-products of one species, but instead are co-products for the other species).

The scope of the IMTA concept is extremely broad and flexible and is always evolving. IMTA can be applied worldwide to open-water and land-based systems, marine and freshwater systems, and temperate and tropical systems. Consequently, it can’t be reduced to a short bureaucratic definition indicating species, type of infrastructures, number of infrastructures, distances, etc. Its versatility is remarkable.

The Skimmer: Can you tell us more about the benefits of doing IMTA?

Chopin: Seaweeds are excellent nutrient scrubbers – especially of dissolved nitrogen, phosphorus, and carbon. IMTA takes advantage of the benefits of nutrients, which in moderation (i.e., within the assimilative capacity of the ecosystem) are co-products and food, not waste or by-products.

Nutrient biomitigation is also not the only ecosystem service provided by seaweeds, and IMTA is more than a story of nutrients. For example:

  • Seaweed cultivation does not require arable soil or the transformation of land (e.g., deforestation with its attendant loss of ecosystem services) for agriculture.
  • It may be stating the obvious, but seaweed aquaculture does not require irrigation as access to water of appropriate quality becomes more and more an issue.
  • Seaweed cultivation does not require the addition of fertilizers and agrochemicals like in terrestrial agriculture, especially in an IMTA setting where the fed aquaculture component provides nutrients.
  • If appropriately designed, seaweed cultivation provides new habitats and can help restore ecosystem functions.
  • While all other components (fed finfish and invertebrates) are oxygen consumers, seaweeds are photosynthetic organisms that produce oxygen and help to avoid coastal hypoxia.
  • By sequestering carbon dioxide dissolved in seawater, seaweeds could also play a significant role in increasing pH in seawater, thereby reducing coastal acidification.
  • While performing photosynthesis, seaweeds also absorb carbon dioxide and sequester carbon, even if in a transitory manner. Consequently, they could slow down global warming, especially if their cultivation is increased and becomes more widespread globally.
  • Seaweeds can be a substitute for fish protein in aquaculture feed, thus reducing the carbon footprint of fed seafood aquaculture.
  • Increasing the production of sustainable, safe, equitable, resilient, and low-carbon sources of food from the ocean (e.g., invertebrates, seaweeds, and finfish) could mitigate food insecurity and reduce emissions from land-based food production (e.g., red meat).
  • The IMTA multi-crop diversification approach (e.g., raising finfish, seaweeds, and invertebrates together) could mitigate and manage economic risk from climate change and coastal acidification impacts.
  • IMTA systems could be associated with wind farms in integrated food and renewable energy parks (IFREP) to reduce the cumulative footprint of these activities.

[These responses are excerpted from a longer interview with Thierry Chopin. Read the full interview.]


Stefano Longo: Aquaculture not a “relief valve” for fishing pressure on wild stocks

Editor’s note: Stefano B. Longo is an environmental sociologist in the Department of Sociology and Anthropology at North Carolina State University. His research examines the relationships between social and ecological systems, with an emphasis on marine ecosystems, political economy, and the globalization of food systems.

The Skimmer: Many people see marine aquaculture as a way to reduce overfishing on wild finfish and invertebrate stocks. You recently looked at whether this is actually occurring. Can you tell us about how you looked at this and what you found?

Longo: There are many pressures on wild finfish and invertebrate stocks from fishing to other human impacts such as climate change and habitat loss. Aquaculture is often presented as a sort of “relief valve” for capture fisheries and a solution to the problems associated with overfishing. Our recent study examined whether aquaculture production does indeed displace fisheries capture (i.e., substitute farmed seafood for wild seafood). We used World Bank and FAO data and multiple models to assess this relationship (i.e., whether and how much aquaculture has displaced fisheries capture) over time within nations around the world. We did not find convincing evidence that global aquaculture production to date has displaced or suppressed fisheries capture.

The Skimmer: So what are some possible reasons why aquaculture isn’t reducing fishing pressure on wild stocks (and may even be increasing pressure on some stocks)?

Longo: There are likely several social explanations for why aquaculture production has not significantly suppressed fisheries capture as expected. Global factors such as economic growth influence seafood production and demand and have likely contributed to overall increases in fisheries production and consumption. Promoting production and consumption of farmed seafood may also stimulate demand for all types of aquatic-based foods, including wild finfish and invertebrates. And many intensive aquaculture operations need fish-based sources of feed such as fishmeal and fish oil that are provided by capture fisheries.

The Skimmer: Do you think there is ever the potential for aquaculture to reduce fishing pressure on wild seafood stocks? What would need to change/be different?

Longo: There is certainly great potential for aquaculture to reduce pressure on wild stocks, but our study suggests that this is not as straightforward as it might seem. Aquaculture is part of a bigger social picture. And the seemingly logical notion that the production of one farmed fish will replace one wild fish does not hold because social factors such as economic development, trade, and commodity production – influence production and consumption. The goals of many aquaculture production systems may not be to displace fisheries capture. Larger transformations in socioecological relationships, especially in the socioeconomic system, are necessary if aquaculture is to help reduce pressure on wild stocks.

 

“To move things in the right direction, production of seafood in aquaculture (and fisheries) could benefit from producing species lower in the food web, such as mollusks… More importantly, socially prioritizing producing food (and in this case seafood protein) as a basic right to meet needs, rather than as simply another commodity in the global economy, and regulating production in an ecologically sound manner, would advance conservation goals while meeting human needs. This would require strong political-economic initiatives (policies) on national and global levels that better plan production, and implement, and enforce regulations that promote sustainability.”

------ Stefano Longo, North Carolina State University


David Little: Use of fish meal and oil in aquadiets is declining, and innovative substitutes are emerging

Editor’s note: David Little is a professor of aquatic resource development with the Aquaculture Systems Research Group at the Institute of Aquaculture of the University of Stirling in the United Kingdom. He specializes in aquatic resource development and capacity building with a focus on Asia.

The Skimmer: Can you tell us a little about the use of fish products derived from wild fish (e.g., fish meal, fish oil) to feed farmed marine species? How much impact does the extraction of wild fish to feed farmed species seem to have on marine ecosystems?

Little: Wild fisheries have been a cornerstone for supporting human diets, probably since we evolved as modern humans, and their exploitation continues to be a critical part of the human food basket. Human interventions into natural ecosystems (both terrestrial and aquatic) to access food have always had impacts; but the demands of industrial urbanized societies in the last two hundred years have greatly accelerated these impacts and in some cases led to losses of biodiversity and ecosystem functionality. Fish that are caught may be used either directly for human food or indirectly as an ingredient in livestock – including fish – diets. Typically, fish used in livestock diets were lower value, often small-sized species. Nowadays fish from feed-fisheries and the byproducts from fish processing are converted into “marine ingredients” e.g., fish meal and fish oil – to feed livestock. Waste material from the processing of wild and farmed fish (e.g., fish heads, viscera, skin) makes up an increasing share – now believed to be more than one third – of the raw material converted to marine ingredients. The extent to which aquaculture is a driver for the fishing of feed fish is up for debate, but this issue is continuously reinforced by media interest in salmon and shrimp that have been dependent on marine ingredients in feed.

When thinking about the impact of the use of marine ingredients on marine ecosystems, it is important to keep several points in mind:

  • Most farming of finfish and other aquatic species actually occurs away from coastlines in freshwater ponds and involves herbivorous and omnivorous species that do not require marine ingredients in their diets (although they may be fed marine ingredients depending on the cost-benefit analysis). There has been rapid growth of marine carnivorous species in recent decades – often in cages located in coastal waters – but this is a relatively small part of the global farmed crop.
     
  • As the farming of marine carnivorous species was getting started, fish were fed moist diets of fresh, ground-up, low-value fish that were by-products of fisheries. This caused all sorts of problems. The unprocessed “feed” fish were highly perishable under tropical conditions and often led to nutritional diseases in the farmed fish. Use of moist diets has also been implicated in pathogen transfer, local pollution, and poor performance of the system as a whole. The shift to formulated diets in which fishmeal and fish oil are just partial ingredients has been a transformative step in the growth of farmed commodity species such as Atlantic salmon and catfish.
     
  • Two trends in the use of marine ingredients have emerged in recent decades. First, the volume of marine ingredients used to feed fish has grown (as a proportion of the total available) while the volume used to feed other livestock has declined. Second, the inclusion rate of fishmeal and oils in aquadiets has declined rapidly. International certification of both fisheries and the aquaculture sector as well as basic economies have driven both of these trends.

The Skimmer: What are the major alternatives to using fish meal and fish oil to feed farmed carnivorous species, and what are some of the pros and cons of moving to these alternative food sources?

Little: As the use of marine ingredients in aquadiets has declined, it has largely been replaced by conventional alternative ingredients also used for terrestrial livestock, e.g., soy-based products to replace fishmeal and terrestrial-derived oils to replace fish oils. Many of these alternative ingredients have their own sustainability issues. Soy production has been responsible for rainforest destruction in South America, palm oil has been responsible for loss of forest habitat and human rights abuses in Southeast Asia, and even rapeseed oil is associated with the loss of pollinating insects in Europe. In addition, these alternative ingredients are associated with other problems. Farmed marine fish fed high levels of terrestrial ingredients do not perform as well (e.g., have lower survival rates and/or poorer individual growth) and can have welfare problems (e.g., morphological/physiological abnormalities and/or reduced resistance to disease). In addition a reduction in marine lipids in the diets fed to farmed fish leads to a reduction in their level of “good fats”, particularly the highly unsaturated fatty acids only available from marine food chains such as DHA and EPA.

The cost of marine ingredients from wild fisheries has steadily increased over the past decades due to their high value and limited volume. These cost increases have stimulated a raft of innovative substitutes that are just now beginning to be used in diet formulations at scale. For example, high protein and lipid products based on various microorganisms are now moving from pilot to production scale. These include:

  • FeedKind, a product developed decades ago using bacteria that use methane as a nutrient source
  • Veramaris, a product based on a microalgae product rich in omega-3 fatty acids
  • Multiple products based on fungi that use low value or waste products (e.g., from the forestry sector) as substrates.

Production of high omega-3 fatty acids from transgenic terrestrial oil crops (e.g., Camelina) has also been demonstrated and, should their inclusion become accepted, this would be the most cost effective approach to the mass production of marine quality lipids.

 

Cellular aquaculture: Seafood without the sea?

Editor’s note: Natalie Rubio is a PhD candidate and New Harvest Research Fellow in Biomedical Engineering at Tufts University. Her research focuses on cellular agriculture. She published a paper “Cell-Based Fish: A Novel Approach to Seafood Production and an Opportunity for Cellular Agriculture” in Frontiers in Sustainable Food Systems earlier this year. In this paper, she suggests that cell-based seafood could promote marine conservation by providing an alternative source of marine animal-based protein (possibly reducing the need for fishing and/or conventional aquaculture). She also discusses how fish cells may be more suitable to being grown in laboratories and mass production than mammal and bird tissues because some fish are adapted to low oxygen and low temperature conditions.

The Skimmer: Can you tell us about what cellular aquaculture is?

Rubio: Instead of catching or farming whole fish to harvest their muscle and fat tissues for fillets, fish sticks, and sushi, we can grow fish muscle and fat stem cells outside of the fish itself. This new approach, called cultured fish/seafood or cellular aquaculture, involves just growing the parts that we want in our food and not the eyes, skin, or bones.

The Skimmer: How far along are we in making cellular aquaculture a reality?

Rubio: There’s still a lot of work to be done before cultured fish products are available to the public. Right now, researchers can generate small amounts of tissue for large amounts of money. To create viable products, companies need to scale up production and greatly reduce manufacturing costs. The first products will likely look like processed fish products (e.g., surimi and fish paste). Products with more structure (e.g., fillets and sushi) are further away.

The Skimmer: What sorts of finfish or shellfish would this work for?

Rubio: In theory, this process can be applied to any type of fish or other animal because all animals have stem cells. It is easier to grow cells from animals that are well researched because we know more about their cell biology. Salmon muscle cells have already been cultured, for example.

The Skimmer: What sort of inputs would be needed, including from the marine environment?

Rubio: A (simplified) cellular aquaculture process involves selecting a target species, isolating cells from that species, expanding the cells in a bioreactor with nutrient-rich growth media, and maturing the cells into structural tissues. So, donor fish are needed for initial cell isolations, growth media (which does not need to come from the marine environment) is required to feed the cells, and bioreactor systems are needed to cultivate the tissues. It's also possible to use an edible material (i.e., scaffold) to grow the cells on – this provides extra surface area for growth and could add to the texture, taste, and nutrition of the final product. Some scaffold materials that researchers have been experimenting with include alginate, cellulose, and chitosan.

Editor’s note: You can read more about cellular aquaculture here and here.

 


[i]According to the UN Food and Agricultural Organization, in 2016, production from aquaculture was 80 million tons – 29 million tons from marine aquaculture and 51 million tons from inland aquaculture. Production from capture fisheries was 91 million tons – 79 million tons from marine capture fisheries and 12 million tons from inland capture fisheries.

[ii] It is also important to note that although we use the term “offshore” in this interview, offshore suggests a given distance (e.g., nautical miles) from the shoreline. In many cases, however, exposed conditions can be found within a few kilometers of shore. In these cases, the terms “aquaculture in high energy environments” and “exposed aquaculture” help express the design and production challenges that these nearshore and offshore industries share.

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