Difference between revisions of "Mariculture"

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Generally it is aquaculture in marine environments.
 
Generally it is aquaculture in marine environments.
 
If one takes a closer look there are different definitions. Some limit mariculture to the raising of marine plants and animals in the ocean itself (EEA, 2008<ref>European Environmental agency; www.glossary.eea.europa.eu/EEAGlossary/M/mariculture, 01/28/08</ref>).  
 
If one takes a closer look there are different definitions. Some limit mariculture to the raising of marine plants and animals in the ocean itself (EEA, 2008<ref>European Environmental agency; www.glossary.eea.europa.eu/EEAGlossary/M/mariculture, 01/28/08</ref>).  
Others also include species from brackish water and include culture methods that take place in salty and brackish water that is not situated in the ocean (CBD, 2004<ref name="CBD">Secretariat of the Convention on Biological Diversity (2004): Solutions for sustainable mariculture-avoiding the adverse effects of mariculture on biological diversity, CBD Technical Series No. 12</ref>) (Wecker, 2006<ref name="wecker">Wecker B (2006): Nährstofffluss in einer geschlossenen Kreislaufanlage mit integrierter Prozesswasserklärung über Algenfilter-Modell und Wirklichkeit.;  http://e-diss.uni-kiel.de/math-nat.html, 02/15/08</ref>)
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Others also include species from brackish water and include culture methods that take place in salty and brackish water that is not situated in the ocean (CBD, 2004<ref name="CBD">Secretariat of the Convention on Biological Diversity (2004): Solutions for sustainable mariculture-avoiding the adverse effects of mariculture on biological diversity, CBD Technical Series No. 12</ref>, Wecker, 2006<ref name="wecker">Wecker B (2006): Nährstofffluss in einer geschlossenen Kreislaufanlage mit integrierter Prozesswasserklärung über Algenfilter-Modell und Wirklichkeit.;  http://e-diss.uni-kiel.de/math-nat.html, 02/15/08</ref>)
 
. Here this wider definition is referred to.
 
. Here this wider definition is referred to.
 
Mariculture can be distinguished from capture fisheries by two criteria: ownership of the stock and deliberate intervention in the production cycle (husbandry). (Naylor et al., 2000<ref name="naylor">Naylor RL, Goldburg RJ, Primavera JH, Kautsky N, Beveridge MCM, Clay J, Folke C, Lubchenko J, Mooney H, Troell M (2000): Effect of aquaculture on world fish supplies; Nature 405, p. 1017-1024</ref>)
 
Mariculture can be distinguished from capture fisheries by two criteria: ownership of the stock and deliberate intervention in the production cycle (husbandry). (Naylor et al., 2000<ref name="naylor">Naylor RL, Goldburg RJ, Primavera JH, Kautsky N, Beveridge MCM, Clay J, Folke C, Lubchenko J, Mooney H, Troell M (2000): Effect of aquaculture on world fish supplies; Nature 405, p. 1017-1024</ref>)
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==Introduction==
 
==Introduction==
 
Mariculture includes a wide range of species and culture methods.
 
Mariculture includes a wide range of species and culture methods.
It is growing fast on a global scale(CBD, 2004<ref name="CBD"/>).  
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It is growing fast on a global scale (CBD, 2004<ref name="CBD"/>).  
This is due to the fact that many fish stocks are overfished and catches are declining (Neori et al., 2004<ref name="neori">Neori A, Chopin T, Troell M, Buschmann AH, Kraemer GP, Halling C, Shpigel M, Yarish C (2004): Integrated aquaculture: rationale, evolution and state of the art emphasizing seaweed biofiltration in modern mariculture; Aquaculture 231, p. 361-391</ref>)(Wecker, 2006<ref name="wecker"/>).  
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This is due to the fact that many fish stocks are overfished and catches are declining (Neori et al., 2004<ref name="neori">Neori A, Chopin T, Troell M, Buschmann AH, Kraemer GP, Halling C, Shpigel M, Yarish C (2004): Integrated aquaculture: rationale, evolution and state of the art emphasizing seaweed biofiltration in modern mariculture; Aquaculture 231, p. 361-391</ref>, Wecker, 2006<ref name="wecker"/>).  
 
At the same time the world population is rising and with it the need for dietary protein (Wecker, 2006<ref name="wecker"/>).  
 
At the same time the world population is rising and with it the need for dietary protein (Wecker, 2006<ref name="wecker"/>).  
 
The expansion of mariculture can reduce pressure on wild fish, shrimps and molluscs, because they reduce their market price and by this the investments in fishing fleets, or they can increase the pressure due to the use of fishmeal in feed for some mariculture-species (Naylor et al., 2000<ref name="naylor">Naylor RL, Goldburg RJ, Primavera JH, Kautsky N, Beveridge MCM, Clay J, Folke C, Lubchenko J, Mooney H, Troell M (2000): Effect of aquaculture on world fish supplies; Nature 405, p. 1017-1024</ref>)
 
The expansion of mariculture can reduce pressure on wild fish, shrimps and molluscs, because they reduce their market price and by this the investments in fishing fleets, or they can increase the pressure due to the use of fishmeal in feed for some mariculture-species (Naylor et al., 2000<ref name="naylor">Naylor RL, Goldburg RJ, Primavera JH, Kautsky N, Beveridge MCM, Clay J, Folke C, Lubchenko J, Mooney H, Troell M (2000): Effect of aquaculture on world fish supplies; Nature 405, p. 1017-1024</ref>)
  
  
Some forms of mariculture provide good quality food and the production is more efficient than that of terrestrial animals (roughly half the level of feed input per unit output is necessary)(CBD, 2004<ref name="CBD"/>)
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Some forms of mariculture provide good quality food and the production is more efficient than that of terrestrial animals (roughly half the level of feed input per unit output is necessary) (CBD, 2004<ref name="CBD"/>).
.
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Due to freshwater scarcity in many areas of the world mariculture is expected to be the future of aquaculture (Wecker, 2006<ref name="wecker"/>).
 
Due to freshwater scarcity in many areas of the world mariculture is expected to be the future of aquaculture (Wecker, 2006<ref name="wecker"/>).
These are the main species that are used in mariculture:
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These are the main species that are used in mariculture (Tab. 1):
  
Top 10 mariculture species in 2000 (CBD, 2004<ref name="CBD"/>)
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;
; m = marine; b = brackish
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[[Image:anpro.jpg|thumb|left|650px|'''Table 1: Top 10 mariculture species in 2000 (CBD, 2004<ref name="CBD"/>); m = marine, b = brackish''']]
[[Image:anpro.jpg|thumb|centre250px|none]]
 
 
   
 
   
  
 
Products obtained from mariculture are not only used directly as food items, but also as inputs for e.g. cosmetics, neutraceuticals, medicines, food additives and many more.
 
Products obtained from mariculture are not only used directly as food items, but also as inputs for e.g. cosmetics, neutraceuticals, medicines, food additives and many more.
  
But mariculture can also have some disadvantages: there are several environmental problems that are associated with it. Their extend depends on species, culture method, stocking density, feed type, husbandry practice, hydrodynamic site conditions and the sensitivity of the receiving ecosystem. (Troell et al., 1999<ref name="troell99">Troell M, Rönnbäck P, Halling C, Kautsky N, Buschmann A (1999): Ecological engineering in aquaculture: use of seaweeds for removing nutrients from intensive aquaculture; Journal of Applied Phycology 11, p. 89-97</ref>)(Wu, 1995<ref name="wu95">Wu RSS (1995): The environmental impact of marine fish culture: Towards a sustainable future; Marine Pollution Bulletin 31, p. 159-166</ref>)
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But mariculture can also have some disadvantages: there are several environmental problems that are associated with it. Their extend depends on species, culture method, stocking density, feed type, husbandry practice, hydrodynamic site conditions and the sensitivity of the receiving ecosystem. (Troell et al., 1999<ref name="troell99">Troell M, Rönnbäck P, Halling C, Kautsky N, Buschmann A (1999): Ecological engineering in aquaculture: use of seaweeds for removing nutrients from intensive aquaculture; Journal of Applied Phycology 11, p. 89-97</ref>, Wu, 1995<ref name="wu95">Wu RSS (1995): The environmental impact of marine fish culture: Towards a sustainable future; Marine Pollution Bulletin 31, p. 159-166</ref>)
  
 
But these problems can be mitigated to a huge extend. And it should not be forgotten, that in the long run mariculture itself is dependent on a good quality of its environment.
 
But these problems can be mitigated to a huge extend. And it should not be forgotten, that in the long run mariculture itself is dependent on a good quality of its environment.
  
 
Mariculture can play an important role, especially in rural areas for food security, economic and social welfare.
 
Mariculture can play an important role, especially in rural areas for food security, economic and social welfare.
In heavily populated coastal areas mariculture is in competition with other human activities for space and other resources. These other activities can for example be: fisheries, tourism, harbour operations, nature conservation and industry.  
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In heavily populated coastal areas mariculture is in competition with other human activities for space and other resources. These other activities can for example be: fisheries, [[tourism]], harbour operations, nature [[conservation]] and industry.  
[[Integrated Coastal Zone Management (ICZM)]] tries to bring these activities in the coastal zone together in a sustainable way. (Wu, 1995<ref name="wu95"/>)(Read and Fernandes, 2003<ref name="read">Read P, Fernandes T (2003): Management of environmental impacts of marine aquaculture in Europe; Aquaculture 226, p. 139-163</ref>)(Wecker, 2006<ref name="wecker"/>)
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[[Integrated Coastal Zone Management (ICZM)]] tries to bring these activities in the coastal zone together in a sustainable way. (Wu, 1995<ref name="wu95"/>, Read and Fernandes, 2003<ref name="read">Read P, Fernandes T (2003): Management of environmental impacts of marine aquaculture in Europe; Aquaculture 226, p. 139-163</ref>, Wecker, 2006<ref name="wecker"/>)
 
In the different countries around the world legislation on mariculture and its enforcement vary widely, this is why they are not considered here.
 
In the different countries around the world legislation on mariculture and its enforcement vary widely, this is why they are not considered here.
 +
;
  
 
==Types of mariculture==
 
==Types of mariculture==
There are different possibilities to group the kinds of mariculture. The first one presented here is the subdivision by species. This is done because different species require different systems that have different characteristics and effects. Only the most common systems will be mentioned.(CBD, 2004<ref name="CBD"/>)
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[[Image:shrimp ponds in Ecuador.jpg|thumb|right|250px|'''Figure 1: Shrimp ponds in Ecuador (www.fishfarming.com 2008)'''<ref>http://www.fishfarming.com/shrimp.html, 01/28/08</ref>)]]
 
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There are different possibilities to group the kinds of mariculture. The first one presented here is the subdivision by species. This is done because different species require different systems that have different characteristics and effects. Only the most common systems will be mentioned (CBD, 2004<ref name="CBD"/>).
  
  
 
'''Mollusc Culture'''
 
'''Mollusc Culture'''
  
Broodstock/seed supply: Bivalve mollusc larvae are either collected from natural grounds using material to which they adhere or produced in hatcheries by artificial fertilization.
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''Broodstock/seed supply:'' Bivalve mollusc larvae are either collected from natural grounds using material to which they adhere or produced in hatcheries by artificial fertilization.
 
 
Growout: Larvae that have set to their substrate are grown in hanging cultures (suspended from floating rafts or long lines on strings, trays, stacks or mesh bags), vertical or rack culture (sticks or platforms), bottom culture (shells, stones, rocks or cement slabs added to the ground), or in land-based systems. (CBD, 2004<ref name="CBD"/>)
 
  
 +
''Growout:'' Larvae that have set to their substrate are grown in hanging cultures (suspended from floating rafts or long lines on strings, trays, stacks or mesh bags), vertical or rack culture (sticks or platforms), bottom culture (shells, stones, rocks or cement slabs added to the ground), or in land-based systems (CBD, 2004<ref name="CBD"/>).
 +
[[Image:TradNoriGrowing2.jpg|thumb|right|250px|'''Figure 2: Traditional Nori Growing (www.seaweed.ie 2008)'''<ref>http://www.seaweed.ie/aquaculture/LowvsHigh.lasso, 01/28/08</ref>)]]
  
  
'''Crustacean Culture'''
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'''Crustacean Culture''' (Fig. 1)
  
[[Image:shrimp ponds in Ecuador.jpg|thumb|right|250px|Figure 1: Shrimp ponds in Ecuador]]
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''Broodstock/seed supply:'' Until last decade the global industry relied on wild-caught larvae or berried (= egg-carrying) females. Nowadays there is a trend towards hatcheries.
Shrimp ponds in Equador(www.fishfarming.com, 2008<ref>www.fishfarming.com/shrimp html, 01/28/08</ref>)
 
Broodstock/seed supply: Until last decade the global industry relied on wild-caught larvae or berried (= egg-carrying) females. Nowadays there is a trend towards hatcheries.
 
  
Growout: takes place in earthen ponds, concrete raceways and tanks. (CBD, 2004<ref name="CBD"/>)
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''Growout:'' takes place in earthen ponds, concrete raceways and tanks (CBD, 2004<ref name="CBD"/>).
  
 +
[[Image:fish_farming.jpg|thumb|right|250px|'''Figure 3: Salmon farm (www.dfo-mpo.gc.ca 2008'''<ref>http://www.dfo-mpo.gc.ca/science/Story/pacific/better_mngmnt_e.htm, 02/29/08</ref>)]]
  
  
'''Marine Plant Culture'''
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'''Marine Plant Culture''' (Fig. 2)
  
 
This includes macro- and micro[[algae]] as well as [[seagrass]]es.
 
This includes macro- and micro[[algae]] as well as [[seagrass]]es.
  
[[Image:TradNoriGrowing2.jpg|thumb|right|250px|Figure 2: Traditional Nori Growing]]
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''Broodstock/seed supply:'' Cultured aquatic plants have complicates life cycles with several intermediate stages. The major source of broodstock is wild collection. Most culture is now dependent on hatchery production of the early life stages (monospores, zoospores, gametophytes, sporophytes) which are attached to growing media and transferred to marine sites. Other propagation methods involve fragmentation.
traditional nori growing(www.seaweed.ie, 2008<ref>www.seaweed.ie/aquaculture/LowvsHigh.lasso, 01/28/08</ref>)
 
Broodstock/seed supply: Cultured aquatic plants have complicates life cycles with several intermediate stages. The major source of broodstock is wild collection. Most culture is now dependent on hatchery production of the early life stages (monospores, zoospores, gametophytes, sporophytes) which are attached to growing media and transferred to marine sites. Other propagation methods involve fragmentation.
 
 
 
Growout: Young plants are cultured by 3 different methods: suspended (longline and raft), bottom cultures at the sea (large rocks or artificial shapes of concrete are placed on the seabed) and inland tank cultures.(CBD, 2004<ref name="CBD"/>)
 
  
 +
''Growout:'' Young plants are cultured by 3 different methods: suspended (longline and raft), bottom cultures at the sea (large rocks or artificial shapes of concrete are placed on the seabed) and inland tank cultures (CBD, 2004<ref name="CBD"/>).
  
  
'''Finfish Culture'''
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'''Finfish Culture''' (Fig. 3)
  
[[Image:fish_farming.jpg|thumb|right|250px|Figure 3: Fish farming]]
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''Broodstock/seed supply:'' The broodstock can be domesticated or a mix of domesticated and wild animals.
salmon farm(www.dfo.mpo.gc.ca<ref>www.dfo.mpo.gc.ca/science/Story/pacific/better_mngmnt_e.htm, 02/29/08</ref>)
 
Broodstock/seed supply: The broodstock can be domesticated or a mix of domesticated and wild animals.
 
 
Most species are grown from larvae or fry produced in hatcheries. There spawning is often induced with a hormone application.
 
Most species are grown from larvae or fry produced in hatcheries. There spawning is often induced with a hormone application.
  
Growout: Cage culture can be divided into inshore and offshore cages and can be fixed, floating or submerged. Inshore cages are located in protected, shallow areas with less water circulation. Offshore cages are located in deep water and open areas with less protection from storm but with better water exchange.  
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''Growout:'' Cage culture can be divided into inshore and offshore cages and can be fixed, floating or submerged. Inshore cages are located in protected, shallow areas with less water circulation. Offshore cages are located in deep water and open areas with less protection from storm but with better water exchange.  
 
Nets and fish pen are located in shallow water and their edges are anchored to the bottom.
 
Nets and fish pen are located in shallow water and their edges are anchored to the bottom.
A typical fish pond system consists of following basic components: pond compartments enclosed by dikes, canals for supply and drainage of water and gates or water control structures.(CBD, 2004<ref name="CBD"/>)
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A typical fish pond system consists of following basic components: pond compartments enclosed by dikes, canals for supply and drainage of water and gates or water control structures (CBD, 2004<ref name="CBD"/>).
 
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[[Image:intensity.jpg|thumb|left|500px|'''Figure 4: Main differences between extensive, semi-intensive and intensive mariculture systems in terms of resource use and potential environmental risk (Tacon and Foster, 2003)'''<ref>Tacon AGJ, Forster IP (2003): Aquafeeds and the environment: political implications; Aquaculture 226, p. 181-189</ref>).]]
 
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Enhancement or Sea Ranching is mostly developed with marine finfish. Both terms refer to the deliberate release of organisms from hatcheries into the natural [[ecosystem]].
Enhancement or Sea Ranching is mostly developed with marine finfish. Both terms refer to the deliberate release of organisms from hatcheries into the natural ecosystem.
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In enhancement, fry are released to restock wild populations.
In enhancement fry are released to restock wild populations.
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In sea ranching, fish are harvested from artificially enclosed areas (CBD, 2004<ref name="CBD"/>).
In ranching fish are harvested from artificially enclosed areas.(CBD, 2004<ref name="CBD"/>)
 
 
 
It is also possible to coculture different species: this will be further described in the section about mitigation.
 
  
 +
It is also possible to co-culture different species: this will be further described in the section about mitigation.
  
Another possibility to group different types of mariculture is depending on the intensity of farming systems:
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Another possibility to group different types of mariculture is depending on the intensity of farming systems (Fig. 4):
[[Image: ]]
 
 
main differences between extensive, semi-intensive and intensive mariculture systems in terms of resource use and potential environmental risk  (Tacon and Foster, 2003<ref>Tacon AGJ, Forster IP (2003): Aquafeeds and the environment: political implications; Aquaculture 226, p. 181-189</ref>)
 
  
 
==Negative environmental impacts==
 
==Negative environmental impacts==
 
Their occurance and extend depend on husbandry parameters (species, culture method, feed type) and the nature of the receiving environment (physics, chemistry, biology).
 
Their occurance and extend depend on husbandry parameters (species, culture method, feed type) and the nature of the receiving environment (physics, chemistry, biology).
An additional factor that plays into the state of the receiving ecosystem is the release of waste products from other anthropogenic sources (e.g. effluents from industry or human settlements or agricultural runoff).
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An additional factor that plays into the state of the receiving [[ecosystem]] is the release of waste products from other anthropogenic sources (e.g. effluents from industry or human settlements or agricultural runoff).
  
  
'''Nutrient pollution /Eutrophication'''
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'''Nutrient pollution / Eutrophication'''
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[[Image:red_tide_genera.v3.jpg|thumb|right|250px|Figure 5: [http://serc.carleton.edu/images/microbelife/topics/red_tide_genera.v3.jpg Algal bloom ] <ref>http://serc.carleton.edu SERC Carleton</ref>]]
  
[[Eutrophication]] defined as nutrient enrichment (mainly N and P) is considered by some the most important pollution threat to marine waters.(Wu, 1999<ref name="wu99">Wu RSS (1999): Eutrophication, Water Borne Pathogens and Xenobiotic Compounds: Environmental Risks and Challenges; Marine Pollution Bulletin 39, p. 11-22</ref>)
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[[Eutrophication]] defined as nutrient enrichment (mainly N and P) is considered by some the most important [[pollution]] threat to marine waters (Wu, 1999<ref name="wu99">Wu RSS (1999): Eutrophication, Water Borne Pathogens and Xenobiotic Compounds: Environmental Risks and Challenges; Marine Pollution Bulletin 39, p. 11-22</ref>).
 
This problem is often mentioned in the context of intensive culture of fish and shrimp, where a lot of artificial feed are used. There waste consisting of uneaten feed and faeces moves down into the benthos: below fish cages in areas with low currents waste sedimentation leads to a shift in benthic populations towards pollutant-resistant-species. But this effect is mostly confined to within a distance of 50-100m from the mariculture facilities.
 
This problem is often mentioned in the context of intensive culture of fish and shrimp, where a lot of artificial feed are used. There waste consisting of uneaten feed and faeces moves down into the benthos: below fish cages in areas with low currents waste sedimentation leads to a shift in benthic populations towards pollutant-resistant-species. But this effect is mostly confined to within a distance of 50-100m from the mariculture facilities.
Another part of the waste products consisting of CO2, dissolved organic carbon and various soluble nutrients (e.g. ammonia and phosphate) move into the water column.(CBD, 2004<ref name="CBD"/>)(Troell et al., 1999<ref name="troell99">Troell M, Rönnbäck P, Halling C, Kautsky N, Buschmann A (1999): Ecological engineering in aquaculture: use of seaweeds for removing nutrients from intensive aquaculture; Journal of Applied Phycology 11, p. 89-97</ref>)
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Another part of the waste products consisting of CO2, dissolved organic carbon and various soluble nutrients (e.g. ammonia and phosphate) move into the water column (CBD, 2004<ref name="CBD"/>, Troell et al., 1999<ref name="troell99">Troell M, Rönnbäck P, Halling C, Kautsky N, Buschmann A (1999): Ecological engineering in aquaculture: use of seaweeds for removing nutrients from intensive aquaculture; Journal of Applied Phycology 11, p. 89-97</ref>).
  
Up to now a huge amount of anthropogenic input of nutrients (not only by mariculture) has caused major changes in structure and functioning of phyto-and zooplankton, benthic and fish communities. (Wu, 1999<ref name="wu99">Wu RSS (1999)(Troell et al., 1999<ref name="troell99"/>)
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Up to now a huge amount of anthropogenic input of nutrients (not only by mariculture) has caused major changes in structure and functioning of phyto-and zooplankton, benthic and fish communities (Wu, 1999<ref name="wu99"/>, Troell et al., 1999<ref name="troell99"/>).
 
Areas with limited water exchange are at especially high risk.
 
Areas with limited water exchange are at especially high risk.
The effluents from fish farming have high N/P-ratios, which are considered a likely cause for the development of (non-) toxic [[algal blooms]].
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The effluents from fish farming have high N/P-ratios, which are considered a likely cause for the development of (non-) toxic [[algal blooms]] (Fig. 5).
algal bloom [(http://soc.carleton.edu<ref>http://soc.carleton.edu/images/microbelife/topics/red_tide_genera.v3.jpg, 02/15/08</ref>)
 
 
   
 
   
[[Image:red_tide_genera.v3.jpg|thumb|right|250px|Figure 6: Algal bloom]]
 
 
  
Algal blooms can shade seafloor vegetation and when they collapse their decay on the seafloor may lead to hypoxia or anoxia and hence mass mortality of benthos and fish. (Troell et al., 2003<ref name="troell03">Troell M, Halling C, Neori A, Chopin T, Buschmann AH, Kautsky N, Yariah C (2003): Integrated mariculture: asking the right questions; Aquaculture 226, p. 69-90</ref>)
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Algal blooms can shade seafloor vegetation and when they collapse their decay on the seafloor may lead to hypoxia or anoxia and hence mass mortality of benthos and fish (Troell et al., 2003<ref name="troell03">Troell M, Halling C, Neori A, Chopin T, Buschmann AH, Kautsky N, Yariah C (2003): Integrated mariculture: asking the right questions; Aquaculture 226, p. 69-90</ref>).
If the species of algae additionally produce toxic substances there is also a public health risk associated with them, mainly via human consumption of filter-feeding shellfish contaminated with the biotoxins. (Wu, 1995<ref name="wu95"/>)
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If the species of algae additionally produce toxic substances there is also a public health risk associated with them, mainly via human consumption of filter-feeding shellfish contaminated with the biotoxins (Wu, 1995<ref name="wu95"/>).
 
Pretty much the opposite of eutrophication may occur at intensive open ocean bivalve cultures: They take nutrients away from the marine foodweb. If this takes place excessively there is less left for other herbivores and phytoplankton and those that live off them.
 
Pretty much the opposite of eutrophication may occur at intensive open ocean bivalve cultures: They take nutrients away from the marine foodweb. If this takes place excessively there is less left for other herbivores and phytoplankton and those that live off them.
Apart from that bivalves take suspended particulate matter and change it into denser particles that fall to the bottom. This might have an effect on benthic communities as well.(CBD, 2004<ref name="CBD"/>)
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Apart from that bivalves take suspended particulate matter and change it into denser particles that fall to the bottom. This might have an effect on benthic communities as well (CBD, 2004<ref name="CBD"/>).
  
  
 
'''Polluting Chemicals'''
 
'''Polluting Chemicals'''
  
Another group of waste products from mariculture that is often released into the environment are certain chemicals:
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Another group of waste products from mariculture that is often released into the environment are certain chemicals (Tab. 2):
chemicals used in mariculture practise that can become pollutants, their sources/uses and impact (CBD, 2004<ref name="CBD"/>)
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[[Image:pollutant.jpg|thumb|right|250px|none]]
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[[Image:pollutant.jpg|thumb|left|550px|'''Table 2: Chemicals used in mariculture practice that can become pollutants, their sources/uses and impact (CBD, 2004<ref name="CBD"/>).''']]
  
  
 
'''Spreading of parasites and diseases'''
 
'''Spreading of parasites and diseases'''
  
Due to crowded and stressful conditions in intensive mariculture there are frequently outbreaks of diseases. The pathogens can be moved to previously disease-free regions by transport of hatchery products like shrimp-postlarvae. And later animals with infections or parasites might escape and spread the pathogens to wild stocks. (CBD, 2004<ref name="CBD"/>)
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Due to crowded and stressful conditions in intensive mariculture there are frequently outbreaks of diseases. The pathogens can be moved to previously disease-free regions by transport of hatchery products like shrimp-postlarvae. And later animals with infections or parasites might escape and spread the pathogens to wild stocks (CBD, 2004<ref name="CBD"/>).
  
  
'''Escapes/ Aliens/ Biodiversity/ Genetics'''
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'''Escapes / Aliens / Biodiversity / Genetics'''
  
Alien species resulting from escaped culture stocks have established far from their home range. Some consider this just more biodiversity, while others think that they predate on or compete with native species and could eventually eliminate these. (CBD, 2004<ref name="CBD"/>)
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Alien species resulting from escaped culture stocks have established far from their home range. Some consider this just more [[biodiversity]], while others think that they predate on or compete with native species and could eventually eliminate these (CBD, 2004<ref name="CBD"/>).
  
 
There is also concern that the escaped fish might lead to a decrease in intraspecific genetic variablility via mixing of escaped cultured animals with wild stocks. By this locally adaptive features of populations will interbreed with fish subject to artificial selection.
 
There is also concern that the escaped fish might lead to a decrease in intraspecific genetic variablility via mixing of escaped cultured animals with wild stocks. By this locally adaptive features of populations will interbreed with fish subject to artificial selection.
 
Research fishing in the Faroese ocean area showed that 20-30% of salmon there are escapes from farms. (Read and Fernandes, 2003<ref name="read"/>)
 
Research fishing in the Faroese ocean area showed that 20-30% of salmon there are escapes from farms. (Read and Fernandes, 2003<ref name="read"/>)
In the future genetically modified fish might also become a problem.(CBD, 2004<ref name="CBD"/>)
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In the future genetically modified fish might also become a problem (CBD, 2004<ref name="CBD"/>).
  
  
 +
'''Farming up and fishing down the food chain / Food security'''
  
'''Farming up and fishing down the food chain/Food security'''
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High value marine carnivorous finfish need animal sources of protein. Most of this comes from marine fish in the form of fish meal. The fish meal is made from small pelagic wild fish e.g. anchoveta and atlantic herring. This practise has two main disadvantages. One is that there is less left for marine predators like seals and seabirds and also commercially valuable predatory fish like cod (CBD, 2004<ref name="CBD"/>).
 
+
The other is concerning human food security. Often 2-5 times more fish protein is put into the farmed species than is supplied by the farmed product. In contrast herbivorous filter feeders contribute to food security (Naylor et al., 2000<ref name="naylor"/>).
High value marine carnivorous finfish need animal sources of protein. Most of this comes from marine fish in the form of fish meal. The fish meal is made from small pelagic wild fish e.g. anchoveta and atlantic herring. This practise has two main disadvantages. One is that there is less left for marine predators like seals and seabirds and also commercially valuable predatory fish like cod (CBD, 2004<ref name="CBD"/>)
 
. The other is concerning human food security. Often 2-5 times more fish protein is put into the farmed species than is supplied by the farmed product. In contrast herbivorous filter feeders contribute to food security. (Naylor et al., 2000<ref name="naylor"/>)
 
  
  
Line 150: Line 136:
  
 
This practice poses several threats to the environment:
 
This practice poses several threats to the environment:
Of course the natural stocks of the target specimen are depleted. This may also lead to problems for species that normally feed on them (e.g. shrimp larvae are a food source for many organisms). But there are also other side effects: bycatch may be very high in some cases and sometimes destructive gear like dredge nets is used.(CBD, 2004<ref name="CBD"/>)
+
Of course the natural stocks of the target specimen are depleted. This may also lead to problems for species that normally feed on them (e.g. shrimp larvae are a food source for many organisms). But there are also other side effects: bycatch may be very high in some cases and sometimes destructive gear like dredge nets is used (CBD, 2004<ref name="CBD"/>).
  
  
'''Habitat degradation/modification'''
+
'''Habitat degradation / modification'''
  
 
In general mariculture can (depending on cultivation method) take a lot of space, which can affect migratory routes and feeding patterns and reproduction of non-target species.  
 
In general mariculture can (depending on cultivation method) take a lot of space, which can affect migratory routes and feeding patterns and reproduction of non-target species.  
One example is the destruction of mangroves to build shrimp ponds there. If these ponds are in operation later their effluents might pose a threat to adjacent mangrove ecosystems. Saltwater intrusion due to active pumping of groundwater into the ponds may lead to additional problems.(Páez-Osuna, 2001<ref>Páez-Osuna F (2001): The environmental impact of shrimp aquaculture: a global perspective; Environmental Pollution 112, p. 229-231</ref>)(CBD, 2004<ref name="CBD"/>)
+
One example is the destruction of mangroves to build shrimp ponds there. If these ponds are in operation later their effluents might pose a threat to adjacent mangrove ecosystems. Saltwater intrusion due to active pumping of groundwater into the ponds may lead to additional problems (Páez-Osuna, 2001<ref>Páez-Osuna F (2001): The environmental impact of shrimp aquaculture: a global perspective; Environmental Pollution 112, p. 229-231</ref>, CBD, 2004<ref name="CBD"/>).
 
 
 
 
  
  
 
'''Acoustic devices'''
 
'''Acoustic devices'''
  
Like underwater exploders are sometimes used in mariculture to deter predators from the farmed animals. This can also stress non-target animals.(CBD, 2004<ref name="CBD"/>)
+
Like underwater exploders are sometimes used in mariculture to deter predators from the farmed animals. This can also stress non-target animals (CBD, 2004<ref name="CBD"/>).
  
 
==Possibilities for mitigation==
 
==Possibilities for mitigation==
Line 171: Line 155:
 
'''Use of enclosed and recirculating systems for shrimp and finfish'''
 
'''Use of enclosed and recirculating systems for shrimp and finfish'''
  
This prevents escapes and aerated settling tanks or other (bio-)filters prevent most particulate nutrients and parts of the dissolved nutrients to enter the natural ecosystems. A disadvantage of them is that they require high initial investment. (CBD, 2004<ref name="CBD"/>)
+
This prevents escapes and aerated settling tanks or other (bio-)filters prevent most particulate nutrients and parts of the dissolved nutrients to enter the natural ecosystems. A disadvantage of them is that they require high initial investment (CBD, 2004<ref name="CBD"/>).
 
 
  
  
 
'''Integrated (multi trophic) aquaculture'''
 
'''Integrated (multi trophic) aquaculture'''
  
Polyculture is defined by the CBD(CBD, 2004<ref name="CBD"/>)
+
Polyculture is defined by the [[Convention on Biological Diversity]] (CBD) as growing two or more species belonging to different trophic levels in the same system (CBD, 2004<ref name="CBD"/>).  
as growing 2 or more species belonging to different trophic levels in the same system.  
 
 
Other refer to this as integrated (multi trophic) aquaculture and use the term polyculture only if the aspect of different trophic levels is not included.
 
Other refer to this as integrated (multi trophic) aquaculture and use the term polyculture only if the aspect of different trophic levels is not included.
 
This form of mariculture is a managed imitation of natural ecoystems:
 
This form of mariculture is a managed imitation of natural ecoystems:
 
The effluents from intensive fed culture of finfish or shrimps are taken up by bivalves and plants. Marine plants use sunlight and assimilate dissolved inorganic nutrients from the water, while bivalves filter organic suspended particles which can be uneaten feed or phytoplankton from the effluents. The marine plants can be phytoplankton that is then eaten by the bivalves or seaweeds that can be sold (like the bivalves).  
 
The effluents from intensive fed culture of finfish or shrimps are taken up by bivalves and plants. Marine plants use sunlight and assimilate dissolved inorganic nutrients from the water, while bivalves filter organic suspended particles which can be uneaten feed or phytoplankton from the effluents. The marine plants can be phytoplankton that is then eaten by the bivalves or seaweeds that can be sold (like the bivalves).  
 
This has several advantages:
 
This has several advantages:
-waste of one species can be converted to products that have an economic value, this means a higher income and the diversification of the mariculture production also reduces the financial risk
+
:*waste of one species can be converted to products that have an economic value, this means a higher income and the diversification of the mariculture production also reduces the financial risk
-the adverse environmental impacts of intensive culture of carnivores are reduced and sustainability can be reached, as seaweeds do not only counterbalance the nutrient inputs by the fish and shrimp ,but also other metabolic aspects such as dissolved oxygen, acidity and CO2-levels
+
:*the adverse environmental impacts of intensive culture of carnivores are reduced and sustainability can be reached, as seaweeds do not only counterbalance the nutrient inputs by the fish and shrimp, but also other metabolic aspects such as dissolved oxygen, acidity and CO<sub>2</sub>-levels
-hardly extra effort is necessary to fulfil the requirements of organic aquaculture, a lucrative market.
+
:*hardly extra effort is necessary to fulfil the requirements of organic aquaculture, a lucrative market.
This system is considered a good solution by many scientists.
+
This system is considered a good solution by many scientists (Chopin et al., 2001<ref> Chopin T, Buschmann AH, Halling C, Troell M, Kautsky N, Neori A, Kraemer GP, Zertuche-González, Yarish C, Nefus C (2001): Integrating seaweeds into marine aquaculture systems: a key toward sustainability; Journal of Phycology 37, p 975-986</ref>, Neori et al., 2004<ref name="neori"/>, CBD, 2004<ref name="CBD"/>, Troell et al., 2003<ref name="troell03"/>)
(Chopin et al., 2001<ref> Chopin T, Buschmann AH, Halling C, Troell M, Kautsky N, Neori A, Kraemer GP, Zertuche-González, Yarish C, Nefus C (2001): Integrating seaweeds into marine aquaculture systems: a key toward sustainability; Journal of Phycology 37, p 975-986</ref>)(Neori et al., 2004<ref name="neori"/>) (CBD, 2004<ref name="CBD"/>)(Troell et al., 2003<ref name="troell03"/>)
 
 
 
 
 
  
  
 
'''Best site selection'''
 
'''Best site selection'''
  
An example is to take into account water exchange rates and currents that dilute the waste(CBD, 2004<ref name="CBD"/>)
+
An example is to take into account water exchange rates and currents that dilute the waste (CBD, 2004<ref name="CBD"/>).
.
+
If dilution is a long-term-solution is questionable.
+
Whether dilution is a long-term-solution, is questionable.
  
  
Line 202: Line 181:
  
 
This could be realised by setting a threshold for stocking density or a careful selection of farmed species.  
 
This could be realised by setting a threshold for stocking density or a careful selection of farmed species.  
Additionally the carrying capacity of the ecosystem to process waste products should be taken into account. (CBD, 2004<ref name="CBD"/>)
+
Additionally the carrying capacity of the ecosystem to process waste products should be taken into account (CBD, 2004<ref name="CBD"/>).
 
Although it is difficult to assess, especially in coastal zones with cumulative pressure from several anthropogenic activities.
 
Although it is difficult to assess, especially in coastal zones with cumulative pressure from several anthropogenic activities.
Another new idea for intensive fish farming in cages that may help to prevent degradation of benthic habitats is this: fixing cages at only one mooring on a long line so that they can float over a large area (moved by e.g. wind and tidal currents) may help to reduce local amounts of sedimentation.(Goudey et al., 2001<ref>Goudey CA, Loverich G, Kite-Powell H, Costa-Pierce BA (2001): Mitigating the environmental effects of mariculture through single-point moorings (SPMs) and drifting cages; ICES Journal of Marine Science 58, p. 497-503</ref>)
+
Another new idea for intensive fish farming in cages that may help to prevent degradation of benthic habitats is this: fixing cages at only one mooring on a long line so that they can float over a large area (moved by e.g. wind and tidal currents) may help to reduce local amounts of sedimentation (Goudey et al., 2001<ref>Goudey CA, Loverich G, Kite-Powell H, Costa-Pierce BA (2001): Mitigating the environmental effects of mariculture through single-point moorings (SPMs) and drifting cages; ICES Journal of Marine Science 58, p. 497-503</ref>).
  
  
 +
'''Better feeding management: to reduce waste ...'''
  
'''Better feeding management: to reduce waste…'''
+
One example for this is the improvement of feed formulations (reducing N and P in the diets (N is assumed to be the limiting nutrient for phytoplankton growth in marine waters)).
 
 
One example for this is the improvement of feed formulations (reducing N and P in the diets (N is assumed to be the limiting nutrient for phytoplankton growth in marine waters))
 
 
Another example is the use of efficient strains of the farmed species.
 
Another example is the use of efficient strains of the farmed species.
 
It might also be helpful to raise the awareness of farm workers.
 
It might also be helpful to raise the awareness of farm workers.
In shrimp ponds natural feed items like zooplankton and benthic organisms could be used as a supplement to artificial diets.(CBD, 2004<ref name="CBD"/>)
+
In shrimp ponds natural feed items like zooplankton and benthic organisms could be used as a supplement to artificial diets (CBD, 2004<ref name="CBD"/>).
  
  
'''and improve food security:'''
+
'''... and improve food security:'''
  
An expansion of farming of fish of low trophic levels and the reduction of fish meal and oils inputs in feed could be helpful.(Naylor et al., 2000<ref name="naylor"/>)
+
An expansion of farming of fish of low trophic levels and the reduction of fish meal and oils inputs in feed could be helpful (Naylor et al., 2000<ref name="naylor"/>).
  
Reducing fish meal in feed and improving feed efficiency are already priorities in the mariculture industry as feed is the largest cost point in many intensive culture systems and the prices of fish meal continue to rise.
+
Reducing fish meal in feed and improving feed efficiency are already priorities in the mariculture industry as feed is the largest cost point in many intensive culture systems and the prices of fish meal continue to rise (Naylor et al., 2000<ref name="naylor"/>).
(Naylor et al., 2000<ref name="naylor"/>)
 
  
  
 
'''Production of larvae in mariculture facilities instead of taking them from the wild '''(CBD, 2004<ref name="CBD"/>)
 
'''Production of larvae in mariculture facilities instead of taking them from the wild '''(CBD, 2004<ref name="CBD"/>)
 
 
  
  
Line 234: Line 209:
 
Probiotics can be used to improve the water quality.
 
Probiotics can be used to improve the water quality.
 
Vaccination is available against some important infectious diseases.
 
Vaccination is available against some important infectious diseases.
Improved monitoring and quarantine stations might also show positive effects.(CBD, 2004<ref name="CBD"/>)
+
Improved monitoring and quarantine stations might also show positive effects (CBD, 2004<ref name="CBD"/>).
  
  
 +
'''Reducing the use of hormones'''
  
'''Reducing the use of hormones'''
+
Alternatives can be proper genetic selection programmes and the use of photoperiod management in the industrial production of salmon (CBD, 2004<ref name="CBD"/>).
 +
 
 +
==See also==
  
Alternatives can be proper genetic selection programmes and the use of photoperiod management in the industrial production of salmon. (CBD, 2004<ref name="CBD"/>)
+
===Internal Links===
 +
*[[Impact of fisheries on coastal systems ]]
 +
*[[Effects of fisheries on European marine biodiversity]]
 +
*[[ALGADEC - Detection of toxic algae with a semi-automated nucleic acid biosensor]]
  
 
==References==
 
==References==
Line 248: Line 229:
  
 
{{author
 
{{author
|AuthorID=280
+
|AuthorID=16480
 
|AuthorFullName= Honnens, Hilke
 
|AuthorFullName= Honnens, Hilke
 
|AuthorName=Hilke}}
 
|AuthorName=Hilke}}
  
 
[[Category:Coastal and marine aquaculture]]
 
[[Category:Coastal and marine aquaculture]]
 +
[[Category:Theme 4]]
 +
[[Category:Coastal and marine pollution]]
 +
[[Category:Techniques and methods in coastal management]]
 +
[[Category:Coastal trade and commerce]]
 +
[[Category:Coastal and marine human activities]]
 +
[[Category:Coastal and marine issues and impacts]]
 +
[[Category:Access to coastal zones and resources]]
 +
[[Category:Biodiversity and habitat loss]]
 +
[[Category:Health and safety in coastal and marine areas]]
 +
[[Category:Resource depletion and degradation]]

Revision as of 23:48, 2 January 2017

Definition

Generally it is aquaculture in marine environments. If one takes a closer look there are different definitions. Some limit mariculture to the raising of marine plants and animals in the ocean itself (EEA, 2008[1]). Others also include species from brackish water and include culture methods that take place in salty and brackish water that is not situated in the ocean (CBD, 2004[2], Wecker, 2006[3]) . Here this wider definition is referred to. Mariculture can be distinguished from capture fisheries by two criteria: ownership of the stock and deliberate intervention in the production cycle (husbandry). (Naylor et al., 2000[4])

Introduction

Mariculture includes a wide range of species and culture methods. It is growing fast on a global scale (CBD, 2004[2]). This is due to the fact that many fish stocks are overfished and catches are declining (Neori et al., 2004[5], Wecker, 2006[3]). At the same time the world population is rising and with it the need for dietary protein (Wecker, 2006[3]). The expansion of mariculture can reduce pressure on wild fish, shrimps and molluscs, because they reduce their market price and by this the investments in fishing fleets, or they can increase the pressure due to the use of fishmeal in feed for some mariculture-species (Naylor et al., 2000[4])


Some forms of mariculture provide good quality food and the production is more efficient than that of terrestrial animals (roughly half the level of feed input per unit output is necessary) (CBD, 2004[2]).

Due to freshwater scarcity in many areas of the world mariculture is expected to be the future of aquaculture (Wecker, 2006[3]). These are the main species that are used in mariculture (Tab. 1):

Table 1: Top 10 mariculture species in 2000 (CBD, 2004[2]); m = marine, b = brackish


Products obtained from mariculture are not only used directly as food items, but also as inputs for e.g. cosmetics, neutraceuticals, medicines, food additives and many more.

But mariculture can also have some disadvantages: there are several environmental problems that are associated with it. Their extend depends on species, culture method, stocking density, feed type, husbandry practice, hydrodynamic site conditions and the sensitivity of the receiving ecosystem. (Troell et al., 1999[6], Wu, 1995[7])

But these problems can be mitigated to a huge extend. And it should not be forgotten, that in the long run mariculture itself is dependent on a good quality of its environment.

Mariculture can play an important role, especially in rural areas for food security, economic and social welfare. In heavily populated coastal areas mariculture is in competition with other human activities for space and other resources. These other activities can for example be: fisheries, tourism, harbour operations, nature conservation and industry. Integrated Coastal Zone Management (ICZM) tries to bring these activities in the coastal zone together in a sustainable way. (Wu, 1995[7], Read and Fernandes, 2003[8], Wecker, 2006[3]) In the different countries around the world legislation on mariculture and its enforcement vary widely, this is why they are not considered here.

Types of mariculture

Figure 1: Shrimp ponds in Ecuador (www.fishfarming.com 2008)[9])

There are different possibilities to group the kinds of mariculture. The first one presented here is the subdivision by species. This is done because different species require different systems that have different characteristics and effects. Only the most common systems will be mentioned (CBD, 2004[2]).


Mollusc Culture

Broodstock/seed supply: Bivalve mollusc larvae are either collected from natural grounds using material to which they adhere or produced in hatcheries by artificial fertilization.

Growout: Larvae that have set to their substrate are grown in hanging cultures (suspended from floating rafts or long lines on strings, trays, stacks or mesh bags), vertical or rack culture (sticks or platforms), bottom culture (shells, stones, rocks or cement slabs added to the ground), or in land-based systems (CBD, 2004[2]).

Figure 2: Traditional Nori Growing (www.seaweed.ie 2008)[10])


Crustacean Culture (Fig. 1)

Broodstock/seed supply: Until last decade the global industry relied on wild-caught larvae or berried (= egg-carrying) females. Nowadays there is a trend towards hatcheries.

Growout: takes place in earthen ponds, concrete raceways and tanks (CBD, 2004[2]).

Figure 3: Salmon farm (www.dfo-mpo.gc.ca 2008[11])


Marine Plant Culture (Fig. 2)

This includes macro- and microalgae as well as seagrasses.

Broodstock/seed supply: Cultured aquatic plants have complicates life cycles with several intermediate stages. The major source of broodstock is wild collection. Most culture is now dependent on hatchery production of the early life stages (monospores, zoospores, gametophytes, sporophytes) which are attached to growing media and transferred to marine sites. Other propagation methods involve fragmentation.

Growout: Young plants are cultured by 3 different methods: suspended (longline and raft), bottom cultures at the sea (large rocks or artificial shapes of concrete are placed on the seabed) and inland tank cultures (CBD, 2004[2]).


Finfish Culture (Fig. 3)

Broodstock/seed supply: The broodstock can be domesticated or a mix of domesticated and wild animals. Most species are grown from larvae or fry produced in hatcheries. There spawning is often induced with a hormone application.

Growout: Cage culture can be divided into inshore and offshore cages and can be fixed, floating or submerged. Inshore cages are located in protected, shallow areas with less water circulation. Offshore cages are located in deep water and open areas with less protection from storm but with better water exchange. Nets and fish pen are located in shallow water and their edges are anchored to the bottom. A typical fish pond system consists of following basic components: pond compartments enclosed by dikes, canals for supply and drainage of water and gates or water control structures (CBD, 2004[2]).

Figure 4: Main differences between extensive, semi-intensive and intensive mariculture systems in terms of resource use and potential environmental risk (Tacon and Foster, 2003)[12]).

Enhancement or Sea Ranching is mostly developed with marine finfish. Both terms refer to the deliberate release of organisms from hatcheries into the natural ecosystem. In enhancement, fry are released to restock wild populations. In sea ranching, fish are harvested from artificially enclosed areas (CBD, 2004[2]).

It is also possible to co-culture different species: this will be further described in the section about mitigation.

Another possibility to group different types of mariculture is depending on the intensity of farming systems (Fig. 4):

Negative environmental impacts

Their occurance and extend depend on husbandry parameters (species, culture method, feed type) and the nature of the receiving environment (physics, chemistry, biology). An additional factor that plays into the state of the receiving ecosystem is the release of waste products from other anthropogenic sources (e.g. effluents from industry or human settlements or agricultural runoff).


Nutrient pollution / Eutrophication

Eutrophication defined as nutrient enrichment (mainly N and P) is considered by some the most important pollution threat to marine waters (Wu, 1999[14]). This problem is often mentioned in the context of intensive culture of fish and shrimp, where a lot of artificial feed are used. There waste consisting of uneaten feed and faeces moves down into the benthos: below fish cages in areas with low currents waste sedimentation leads to a shift in benthic populations towards pollutant-resistant-species. But this effect is mostly confined to within a distance of 50-100m from the mariculture facilities. Another part of the waste products consisting of CO2, dissolved organic carbon and various soluble nutrients (e.g. ammonia and phosphate) move into the water column (CBD, 2004[2], Troell et al., 1999[6]).

Up to now a huge amount of anthropogenic input of nutrients (not only by mariculture) has caused major changes in structure and functioning of phyto-and zooplankton, benthic and fish communities (Wu, 1999[14], Troell et al., 1999[6]). Areas with limited water exchange are at especially high risk. The effluents from fish farming have high N/P-ratios, which are considered a likely cause for the development of (non-) toxic algal blooms (Fig. 5).


Algal blooms can shade seafloor vegetation and when they collapse their decay on the seafloor may lead to hypoxia or anoxia and hence mass mortality of benthos and fish (Troell et al., 2003[15]). If the species of algae additionally produce toxic substances there is also a public health risk associated with them, mainly via human consumption of filter-feeding shellfish contaminated with the biotoxins (Wu, 1995[7]). Pretty much the opposite of eutrophication may occur at intensive open ocean bivalve cultures: They take nutrients away from the marine foodweb. If this takes place excessively there is less left for other herbivores and phytoplankton and those that live off them. Apart from that bivalves take suspended particulate matter and change it into denser particles that fall to the bottom. This might have an effect on benthic communities as well (CBD, 2004[2]).


Polluting Chemicals

Another group of waste products from mariculture that is often released into the environment are certain chemicals (Tab. 2):

Table 2: Chemicals used in mariculture practice that can become pollutants, their sources/uses and impact (CBD, 2004[2]).


Spreading of parasites and diseases

Due to crowded and stressful conditions in intensive mariculture there are frequently outbreaks of diseases. The pathogens can be moved to previously disease-free regions by transport of hatchery products like shrimp-postlarvae. And later animals with infections or parasites might escape and spread the pathogens to wild stocks (CBD, 2004[2]).


Escapes / Aliens / Biodiversity / Genetics

Alien species resulting from escaped culture stocks have established far from their home range. Some consider this just more biodiversity, while others think that they predate on or compete with native species and could eventually eliminate these (CBD, 2004[2]).

There is also concern that the escaped fish might lead to a decrease in intraspecific genetic variablility via mixing of escaped cultured animals with wild stocks. By this locally adaptive features of populations will interbreed with fish subject to artificial selection. Research fishing in the Faroese ocean area showed that 20-30% of salmon there are escapes from farms. (Read and Fernandes, 2003[8]) In the future genetically modified fish might also become a problem (CBD, 2004[2]).


Farming up and fishing down the food chain / Food security

High value marine carnivorous finfish need animal sources of protein. Most of this comes from marine fish in the form of fish meal. The fish meal is made from small pelagic wild fish e.g. anchoveta and atlantic herring. This practise has two main disadvantages. One is that there is less left for marine predators like seals and seabirds and also commercially valuable predatory fish like cod (CBD, 2004[2]). The other is concerning human food security. Often 2-5 times more fish protein is put into the farmed species than is supplied by the farmed product. In contrast herbivorous filter feeders contribute to food security (Naylor et al., 2000[4]).


Catching broodstock from the wild

This practice poses several threats to the environment: Of course the natural stocks of the target specimen are depleted. This may also lead to problems for species that normally feed on them (e.g. shrimp larvae are a food source for many organisms). But there are also other side effects: bycatch may be very high in some cases and sometimes destructive gear like dredge nets is used (CBD, 2004[2]).


Habitat degradation / modification

In general mariculture can (depending on cultivation method) take a lot of space, which can affect migratory routes and feeding patterns and reproduction of non-target species. One example is the destruction of mangroves to build shrimp ponds there. If these ponds are in operation later their effluents might pose a threat to adjacent mangrove ecosystems. Saltwater intrusion due to active pumping of groundwater into the ponds may lead to additional problems (Páez-Osuna, 2001[16], CBD, 2004[2]).


Acoustic devices

Like underwater exploders are sometimes used in mariculture to deter predators from the farmed animals. This can also stress non-target animals (CBD, 2004[2]).

Possibilities for mitigation

Many of the aforementioned possible negative environmental impacts of mariculture can be mitigated. In the following section some measures to do so are presented:


Use of enclosed and recirculating systems for shrimp and finfish

This prevents escapes and aerated settling tanks or other (bio-)filters prevent most particulate nutrients and parts of the dissolved nutrients to enter the natural ecosystems. A disadvantage of them is that they require high initial investment (CBD, 2004[2]).


Integrated (multi trophic) aquaculture

Polyculture is defined by the Convention on Biological Diversity (CBD) as growing two or more species belonging to different trophic levels in the same system (CBD, 2004[2]). Other refer to this as integrated (multi trophic) aquaculture and use the term polyculture only if the aspect of different trophic levels is not included. This form of mariculture is a managed imitation of natural ecoystems: The effluents from intensive fed culture of finfish or shrimps are taken up by bivalves and plants. Marine plants use sunlight and assimilate dissolved inorganic nutrients from the water, while bivalves filter organic suspended particles which can be uneaten feed or phytoplankton from the effluents. The marine plants can be phytoplankton that is then eaten by the bivalves or seaweeds that can be sold (like the bivalves). This has several advantages:

  • waste of one species can be converted to products that have an economic value, this means a higher income and the diversification of the mariculture production also reduces the financial risk
  • the adverse environmental impacts of intensive culture of carnivores are reduced and sustainability can be reached, as seaweeds do not only counterbalance the nutrient inputs by the fish and shrimp, but also other metabolic aspects such as dissolved oxygen, acidity and CO2-levels
  • hardly extra effort is necessary to fulfil the requirements of organic aquaculture, a lucrative market.

This system is considered a good solution by many scientists (Chopin et al., 2001[17], Neori et al., 2004[5], CBD, 2004[2], Troell et al., 2003[15])


Best site selection

An example is to take into account water exchange rates and currents that dilute the waste (CBD, 2004[2]).

Whether dilution is a long-term-solution, is questionable.


Better management to reduce nutrient input effect

This could be realised by setting a threshold for stocking density or a careful selection of farmed species. Additionally the carrying capacity of the ecosystem to process waste products should be taken into account (CBD, 2004[2]). Although it is difficult to assess, especially in coastal zones with cumulative pressure from several anthropogenic activities. Another new idea for intensive fish farming in cages that may help to prevent degradation of benthic habitats is this: fixing cages at only one mooring on a long line so that they can float over a large area (moved by e.g. wind and tidal currents) may help to reduce local amounts of sedimentation (Goudey et al., 2001[18]).


Better feeding management: to reduce waste ...

One example for this is the improvement of feed formulations (reducing N and P in the diets (N is assumed to be the limiting nutrient for phytoplankton growth in marine waters)). Another example is the use of efficient strains of the farmed species. It might also be helpful to raise the awareness of farm workers. In shrimp ponds natural feed items like zooplankton and benthic organisms could be used as a supplement to artificial diets (CBD, 2004[2]).


... and improve food security:

An expansion of farming of fish of low trophic levels and the reduction of fish meal and oils inputs in feed could be helpful (Naylor et al., 2000[4]).

Reducing fish meal in feed and improving feed efficiency are already priorities in the mariculture industry as feed is the largest cost point in many intensive culture systems and the prices of fish meal continue to rise (Naylor et al., 2000[4]).


Production of larvae in mariculture facilities instead of taking them from the wild (CBD, 2004[2])


Preventing disease outbreaks and transmission and with it the use of pesticides, piscicides and parasiticides and antibiotics

This can be achieved by establishing lower stocking densities and leaving larger distances between individual farms. Probiotics can be used to improve the water quality. Vaccination is available against some important infectious diseases. Improved monitoring and quarantine stations might also show positive effects (CBD, 2004[2]).


Reducing the use of hormones

Alternatives can be proper genetic selection programmes and the use of photoperiod management in the industrial production of salmon (CBD, 2004[2]).

See also

Internal Links

References

  1. European Environmental agency; www.glossary.eea.europa.eu/EEAGlossary/M/mariculture, 01/28/08
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 2.24 2.25 2.26 2.27 2.28 Secretariat of the Convention on Biological Diversity (2004): Solutions for sustainable mariculture-avoiding the adverse effects of mariculture on biological diversity, CBD Technical Series No. 12
  3. 3.0 3.1 3.2 3.3 3.4 Wecker B (2006): Nährstofffluss in einer geschlossenen Kreislaufanlage mit integrierter Prozesswasserklärung über Algenfilter-Modell und Wirklichkeit.; http://e-diss.uni-kiel.de/math-nat.html, 02/15/08
  4. 4.0 4.1 4.2 4.3 4.4 Naylor RL, Goldburg RJ, Primavera JH, Kautsky N, Beveridge MCM, Clay J, Folke C, Lubchenko J, Mooney H, Troell M (2000): Effect of aquaculture on world fish supplies; Nature 405, p. 1017-1024
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The main author of this article is Honnens, Hilke
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Citation: Honnens, Hilke (2017): Mariculture. Available from http://www.coastalwiki.org/wiki/Mariculture [accessed on 28-03-2024]