Course:EOSC270/2022/Group 16 - Effects of Sea Cage Aquaculture on surrounding Marine Ecosystems

From UBC Wiki

What is the problem?

Sea Cage farms off the coast of Greece

Background:

Grieg Seafood operates a salmon farm in Clio Channel, Broughton Archipelago, British Columbia, Canada.

The farming of fish in temperate regions using cage aquaculture has become a large source of income for countries that have coastal regions. Aquaculture makes up around 43 percent of the aquatic food that humans consume per year and has seen considerable growth over the last 50 years.[1] The aquaculture business is still growing and is an important portion of the economy of many developing coastal countries. Cage aquaculture is a form of fish farming in which fish are grown in open water using a buoyant cage. This creates an open system.

Human Action:

In these cages, fish are kept in high density low volume environments that are efficient for farming, but have adverse effects on the environment the cages are placed in. The increasing efficiency and technological advancements in modern day aquaculture have caused a boom in the industry which will likely continue into the future.[1] Decreasing coastal space is also driving cage fish farming in offshore areas. Because of the expanding human population, aquaculture will adapt to using more cage farming methods and will therefore take up more coastal space.  

Where is this happening:

Countries like China, Norway, and Chile are all big proprietors of aquaculture (such as cage farming) and are running out of coastal space to place farms.[2] This is causing a shift to offshore cage farming, which could result in a massive influx of food for the growing human population if constructed.[3] Because of how efficient this would be for food production; it is most likely that this type of cage farming would become the new norm for fish aquaculture. This type of farming has a plethora of effects on the marine ecosystems that surround it. These effects have not been studied in depth, and not much is known about the scale of these impacts on the ocean at large. Some studies conclude that the effects of farming like this are almost nonexistent at a distance from the farms themselves,[1] while others conclude that the data we have right now is not accurate enough to show what impacts these farms have in different benthic regions of the ocean.[4]  

Extent of the Problem:

Fish that are raised in these farms are prone to spreading diseases that may contaminate and spread throughout surrounding ecosystems, which can have adverse effects on the local fauna population. The large volume of organisms in these cages produce a massive amount of organic waste, which is the main factor that affects ocean life. This is because the overwhelming amount of organic waste causes a massive bloom of aerobic bacteria. These bacteria consume copious amounts of oxygen, causing the decline in populations of other aerobic creatures, and an increase of pathogenic bacteria.[5]

How does this problem impact marine ecosystems?

Due to the unorthodox environment and heavy human involvement, fish raised in cage aquaculture has been found to affect several factors in the external marine ecosystem.

Caulerpa taxifolia, a prominent invasive species of algae in the Mediterranean.

Effect on the ecosystem:

Invasive species are often introduced to new environments as a result of cage aquaculture. Using the Mediterranean Sea as a specific example, types of macrophyte and shellfish otherwise foreign to the area have been known to be introduced in the process of aquaculture.[6] This is particularly prominent in the western region of the Mediterranean, where 73% of known macrophyte introduction was attributed to aquaculture practices.[6] While the invasive species themselves have varied effects on the environment, an example of an especially dominant invasive species in the region is the Caulerpa taxifolia (killer alga); through producing chemicals toxic to other algae and its high fitness,[6] it has colonized much of the French and Italian Rivieras.[7]

Effect on Organisms:  

Leakage of chemical agents used in aquaculture is another notable effect, such as with antibiotics used in antibacterial therapy.[6] This can occur through multiple processes, such as cultured fish failing to metabolize these drugs when ingested and excreting them into the water through feces, or when food pellets inserted with these agents are uneaten and spread through the water in a similar fashion.[8] Digested agents can also be excreted out into the environment in the form of urine.[9] While there has yet to be sufficient research on the effects of these antibiotics lying undegraded in underwater sediment or their direct effects on most surrounding organisms, it is known that their dispersal also leads to local pathogens becoming resistant to the chemicals in question, as antibiotic-resistant bacteria were observed to be more concentrated in areas close to cages.[9]

Posidonia oceanica, an example of an important primary producer with reduced standing biomass and production under cages.

Subsequently, the excretion of cage fish feces into the external environment is also known to cause other issues- for example, a noticeable decrease in seagrass activity. Posidonia oceanica, or Mediterranean tapeweed, is a widespread and essential source of necessities such as food, shelter, and nursery for many organisms. [6] A study of this variety of seagrass under aquaculture cages was conducted, where production and standing biomass were each found to decrease by over 60% [10]. Similar decreases in standing carbon and nitrogen were noted, as well as a 48% decrease in standing phosphorus [10], indicating increased nutrient loss.

Other direct effects of cage aquaculture on surrounding external wildlife have also been noted. Predators that are drawn to these areas by the concentration of potential prey  are sometimes caught in nets or killed by farmers ;[6] negative impacts to predators as a result of aquaculture are particularly significant for endangered species, as they are driven to attack cages due to scarcity of food.[6] On the other hand, some instances show positive effects for predators- uneaten food and waste attract concentrations of wild fish close to the cages, which in turn can provide easy prey for certain predators. However, this potentially causes imbalance for other trophic levels in the ecosystem that are affected by this benefit for predators such as zooplankton and cephalopods[11].

What is the extent of the problem?

Aquaculture and Marine Protected Areas

While aquaculture farms can have massive detrimental effects on the surrounding ecosystem, there are still many farms located in designated Marine Protected Areas (MPAs). Most of those farms existed before the area was declared an MPA, and are allowed to continue operating on the condition that their ecological effects are closely monitored. Scotland monitors five active finfish farms within MPAs to ensure the site uses “good practices”, as defined by their marine authority.18

Good practices can only go so far, so the EU has created an ecological impact assessment matrix to score aquaculture farms on the level of ecological risk they pose to the local habitat, with 1 star meaning little to no impact and 5 stars meaning severe impact. Habitat impact, nutrient discharge, escapee impact, disease spread risk and chemical discharge all had the worst possible score for potential environmental impacts in sheltered marine aquaculture locations. However, not all types of aquaculture are shown to have severe negative impacts. Suspended and marine supported aquaculture did not score above 3 stars in any of those categories.19

Sheltered locations have the worst issues with waste settling, which can alter benthic (sea floor) habitats and smother corals and invertebrates. The change in nutrient balances has also been shown to alter an ecosystem from a carbon sink into a source of organic carbon. If ocean currents are not particularly strong and the water is not very deep, aquacultures can increase heavy metal buildup in the sediments and fish populations as well. However, creating a combination of suspended or marine supported aquaculture and finfish farms will significantly decease overall ecological impact.20

Overfishing is a massive problem worldwide, and aquaculture is one option to decrease the pressure on existing wild fish populations while maintaining global supply. It is estimated that by 2025, aquaculture will supply 52% of the world’s seafood consumption. This means although it has many negative consequences, finfish aquaculture is necessary to support the global demand for fish.21

Given the impact, what are the solutions?

An aquaculture recirculating system where biofiltration removes toxic ammonia produced by the fish away from the water.

Local Solutions:

Lake farming:

In lake farming fish are isolated into artificial lakes or ponds is usually situated on the coastline putting them away from marine habitats. Traditionally this method is also very devastating to local ecosystems. The wastewater is usually pumped directly into coastal environments before bringing in freshwater. However, the major advantage is that it is isolated from the ocean allowing the grower to have more control over the inputs and how much contact it has with the outside world.[12] Wastewater containing antibodies and hormones can be treated before pumping it back to the ocean or it can be recycled back into systems.[5] This significantly lessens issues of parasites and pollution. However, these treatments add costs associated with producing the fish which will be passed on to the consumer. A recirculating system where all the water is kept within the tanks will alleviate most issues surrounding aquaculture.

An example aquaponics system where leafy greens are grown with catfish

Aquaponics:

Aquaponics is the practice of rearing fish alongside vegetables that are grown hydroponically (without soil). There are few plants of economic importance that tolerate marine sea strength therefore this method of fish production is exclusive to a small number of freshwater fish, lots of popular fish species are excluded because of this. By using method, the wastewater is kept within the system ideally eliminating water changes creating a situation where the plants and grow using the nutrients provided from the fish waste keeping the water clean of nitrates. As is commonly done in sealed greenhouses, the environmental impact is kept to a minimum.[13]

Sea cucumbers are a scavenger that can be used in multitrophic aquaculture to consumer fish waste that falls from above

Multitrophic Integration:

Multitrophic integration refers to the rearing of several species of marine organisms in the same area to utilize waste more efficiently from the finfish. By growing extractive aquaculture down current to fed aquaculture such nitrates and fish poop are captured and turned into biomass that can be harvested. Organisms that have been used to capture wastes include Oysters, mussels, kelp and other seaweeds, sea cucumbers.[14] Sea cucumbers are interesting as they are grown below the sea cages focusing on capturing uneaten food and fish poop.[15] Drawbacks include the fact that this only deals with pollution in the form of fish wastes nitrates and does nothing to address pest issues or the use of antibiotics or growth hormones. Sea cucumber rearing also takes up the space in the benthic area displacing and fragmenting this habitat.

Global Solutions

Friends of the Sea is an organization that issues labels to both farmed and wild-caught seafood

Governmental Regulation:

Regulations can bring down antibiotic use in farms and protect sensitive habitats from development.[16] Examples of laws that could be put into place would be limiting the number of fish allowed crowding a fish pen and banning the use of non-native species in aquaculture systems.

Consumer Awareness:

Avoiding fish farming is not possible as countries grow in wealth more people in formerly underdeveloped nations require more fish. Much like the visible effects overfishing has created a demand for sustainably caught fish. As a result of this demand many non-governmental organizations (NGOs) have created labels to put on seafood packaging to advertise the sustainability of the product. This is known as ecolabeling and is a tool that helps consumers make ecologically sound decisions. As aquaculture has become more common place these NGOs should branch out to beginning labeling farmed fish that is farmed sustainably. It has been found that consumers are willing to pay premiums for these types of products[17] which would help cover the costs associated with holistic farming techniques.

References

  1. 1.0 1.1 1.2 Bostock, John; McAndrew, Brendan; Richards, Randolph; Jauncey, Kim; Telfer, Trevor; Lorenzen, Kai; Little, David; Ross, Lindsay; Handisyde, Neil; Gatward, Iain; Corner, Richard (2010). "Aquaculture: global status and trends". In Philosophical Transactions of the Royal Society B: Biological Sciences. 365: 2897–2912.
  2. Dimitriou, Panagiotis; Karakassis, Ioannis; Pitta, Paraskevi; Tsagarak, Tatiana; Apostolaki, Eugenia; Magiopoulos, Iordanis; Nikolioudakis, Nikolaos; Diliberto, Santi; Theodorou, John; Tzovenis, I; Kagalou, Ifigenia; Beza, Paraskev; Manolis, Tsapakis (2010). "Mussel farming in Maliakos Gulf and quality indicators of the marine environment: Good benthic below poor pelagic ecological status". Marine Pollution Bulletin. 101: 784–793.
  3. Holmer, Marianne (2010). "Environmental issues of fish farming in offshore waters: perspectives, concerns and research needs". Aquaculture Environment Interactions. 1: 57–70 – via Inter-Research Science Publisher.
  4. Karakassis, Ioannis; Hatziyanni, Eleni (2000). [doi:10.3354/meps203247 "Benthic disturbance due to fish Farming analyzed under different levels of taxonomic resolution"] Check |url= value (help). Marine Ecology Progress Series. 203: 247–253 – via Inter-Research Science Publisher.
  5. 5.0 5.1 Chávez-Crooker, Pamela; Obreque-Contreras, Johanna (2010). "Bioremediation of aquaculture wastes". Current Opinion in Biotechnology. 21: 313–317 – via Science Direct.
  6. 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Grigorakis, K; Rigos, G (2011). "Aquaculture effects on environmental and public welfare – The case of Mediterranean mariculture". Chemosphere. 85: 899–919 – via Science Direct.
  7. Boudouresque, Charles; Verlaque, Marc (2002). "Biological pollution in the Mediterranean Sea: invasive versus introduced macrophytes". Marine Pollution Bulletin. 44: 32–38 – via Science Direct.
  8. Rigos, George; Nengas, Ioannis; Alexis, Maria; Troisi, Gera (2004). "Potential drug (oxytetracycline and oxolinic acid) pollution from Mediterranean sparid fish farms". Aquatic Toxicology. 69: 281–288 – via Science Direct.
  9. 9.0 9.1 Pepi, Milva; Focardi, Silvano (2021). "Antibiotic-Resistant Bacteria in Aquaculture and Climate Change: A Challenge for Health in the Mediterranean Area". International Journal of Environmental Research and Public Health. 18: 5723 – via Multidisciplinary Digital Publishing Institute.
  10. 10.0 10.1 Apostolaki, Eugenia T; Marbà, Núria; Holmer, Marianne; Karakassis, Ioannis (February 2009). "Fish farming enhances biomass and nutrient loss in Posidonia oceanica (L.) Delile". Estuarine, Coastal and Shelf Science. 81: 390–400. doi:10.1016/j.ecss.2008.11.014 – via Science Direct.
  11. López, Bruno; Bunke, Mandy; Shirai, Julia (2007). "Marine aquaculture off Sardinia Island (Italy): Ecosystem effects evaluated through a trophic mass-balance model". Ecological Modelling. 212: 292–303 – via Science Direct.
  12. Zhang, Shi-Yang; Li, Gu; Wu, Hui-Bi; Liu, Xing-Guo; Yao, Yan-Hong; Tao, Ling; Huang, Liu (2011). "An integrated recirculating aquaculture system (RAS) for land-based fish farming: The effects on water quality and fish production". Aquacultural Engineering. 45 (3): 93–102 – via Science Direct.
  13. Kloas, Werner; et al. (2015). "A new concept for aquaponic systems to improve sustainability, increase productivity, and reduce environmental impacts". Aquaculture Environment Interactions. 7: 179–192 – via ResearchGate. Explicit use of et al. in: |last2= (help)
  14. Chopin, Thierry; Cooper, John Andrew; Reid, Gregor; Cross, Stephen; Moore, Christine (2012). "Open-water integrated multi-trophic aquaculture: environmental biomitigation and economic diversification of fed aquaculture by extractive aquaculture". Reviews in Aquaculture. 4: 209–220 – via Wiley Online Library.
  15. Yokoyama, Hisashi (2013). "Growth and food source of the sea cucumber Apostichopus japonicus cultured below fish cages — Potential for integrated multi-trophic aquaculture". Aquaculture. 372-375: 28–38 – via Science Direct.
  16. Frode, Alfnes; Chen, Xianwen; Rickertsen, Kyrre (2017). "Labeling farmed seafood: A review". Aquaculture Economics & Management. 22: 1–26 – via tandfonline.
  17. Lembo, Giuseppe; Jokumsen, Alfred; Spedicato, Maria; Facchini, Maria; Bitetto, Isabella (2018). "Assessing stakeholder's experience and sensitivity on key issues for the economic growth of organic aquaculture production". Marine Policy. 87: 84–93 – via Science Direct.