Difference between revisions of "Non-native species invasions"

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== Introduction ==
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The introduction of non-native organisms (also called 'alien species') to new marine environments is believed to be one of the greatest threats to the world's marine biodiversity. Together with overexploitation, it has been identified as the major cause of species extinction (Bellard ''et al.'', 2016<ref>Bellard, C., Cassey, P., Blackburn, T.M., 2016. Alien species as a driver of recent extinctions. Biol. Lett. 12, 20150623. https://doi.org/10.1098/rsbl.2015.0623</ref>). An alien or non-native species is one that has been intentionally or accidentally transported and released into an environment outside of its historic or resident geographical range or [[habitat]]. Such [[species]] are described as 'invasive' if they strongly disturb the ecosystem of the new marine environment, with possibly negative economic consequences. Invasive species can profoundly alter the structure and function of marine ecosystems by changing biodiversity and eliminating vital components of the [[food chain]].
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The introduction of harmful aquatic organisms to new marine environments is believed to be one of the four greatest threats to the world's oceans. An alien or non-native species is one that has been intentionally or accidentally transported and released into an environment outside of its historic or resident geographical range or habitat. Such species are described as 'invasive' if they are ecologically and/or economically harmful. Invasive species can dramatically change the structure and function of marine ecosystems by changing biodiversity and eliminating vital components of the food chain.
 
  
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== Functional integrity of species commuities ==
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Even though all seas are interconnected, there are certain dispersion barriers such as salinity, temperature gradient or ocean currents that keep local communities distinct. Two identical habitats can have different species communities with different types of interactions contributing to the global richness of biodiversity. Indigenous, or native species are those living within their natural range (past or present) including the area that it can reach and occupy using its natural dispersal system. By contrast, introduced species are transported either intentionally or accidentally by human-mediated vectors into habitats outside their native range. These species are also termed as alien, exotic, invasive, foreign, non-native, immigrant, neobiota, naturalized, or non-indigenous. Some biota cannot be sufficiently proved to be neither native nor exotic and these are termed cryptogenic species (Carlton, 1996 <ref>Carlton, J.T. (1996). Biological invasions and cryptogenic species. Ecology 77(6): 1653-1655.</ref>)
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== Functional integrity of species communities ==
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Even though all seas are interconnected, there are certain dispersion barriers such as [[salinity]], temperature gradient or [[ocean circulation|ocean currents]] that keep local communities distinct. Two identical habitats can have different species communities with different types of interactions contributing to the global richness of [[biodiversity]]. Indigenous, or native species are those living within their natural range (past or present) including the area that it can reach and occupy using its natural dispersal system. By contrast, introduced species are transported most often accidentally and sometimes intentionally by human-mediated vectors into habitats outside their native range. These species are also termed as alien, exotic, invasive, foreign, non-native, immigrant, neobiota, naturalized, or non-indigenous. Some biota cannot be sufficiently proved to be neither native nor exotic and these are termed cryptogenic species (Carlton, 1996 <ref>Carlton, J.T. 1996. Biological invasions and cryptogenic species. Ecology 77(6): 1653-1655.</ref>)
 
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Through the evolutionary fitness processes, species adjust to each other and adapt to available resources by occupying different ecological niches within communities. Virtually all resources are utilized optimally and all available niches are filled, maximising the biodiversity value. Various factors influence the functional integrity of a community. If changes are occurring gradually over a long timescale species have enough time to adapt and fill available niches. In turn more rapid shifts create niche openings and this has been identified as the main prerequisite of species invasion. Non-native species are found primarily in disturbed areas, such as harbours, bays, estuaries and semi-enclosed seas where the communities are weekened by various types of pollution (Elton, 1958<ref>Elton, C. S. (1958) The Ecology of Invasions by Animals and Plants, Methuen, London. </ref>; Cohen, 2004<ref>Cohen, A. N. (2004). Invasion in the sea. In: Park Science vol. 22, no. 2, fall 2004 pp. 37-41</ref>).
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Through the evolutionary fitness processes, species adjust to each other and adapt to available resources by occupying different ecological niches within communities. Virtually all resources are utilized optimally and all available niches are filled, maximising the biodiversity value. Various factors influence the functional integrity of a community. If changes are occurring gradually over a long timescale species have enough time to adapt and fill available niches. In turn more rapid shifts create niche openings and this has been identified as the main prerequisite of species invasion. Non-native species are found primarily in disturbed areas, such as harbours, bays, [[estuaries]] and semi-enclosed seas where the communities are weakened by various types of pollution (Elton, 1958<ref>Elton, C. S. 1958. The Ecology of Invasions by Animals and Plants, Methuen, London. </ref>; Cohen, 2004<ref>Cohen, A. N. 2004. Invasion in the sea. In: Park Science vol. 22(2): 37-41</ref>).
  
 
== Vectors of introduction ==
 
== Vectors of introduction ==
  
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Whether deliberately or accidentally, people have been transporting whole range of organisms, breaking natural distribution boundaries and interfering with community structures. The unwanted hitchhikers are usually either well hidden or too small to be noticed – for the entire lifespan or just for its part.  
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Whether deliberately or accidentally, people have been transporting whole range of organisms, breaking natural distribution boundaries and interfering with community structures. The unwanted hitchhikers are usually either well-hidden or too small to be noticed – for the entire lifespan or just for its part.  
  
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For most coastal species the open ocean environment is inhospitable, preventing them from spreading into habitats similar to their own but located elsewhere. Distances separating such habitats might be too long to overcome either through their active swimming abilities or passive floating in water currents. Mechanisms by which humanity aids introduction of exotic species are called vectors of introduction and these are chiefly associated with shipment activities, marine aquaculture or ornamental species trade. Other vectors include the international transport and sale of live marine bait, live seafood, and live organisms for research and education.
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For most coastal species the open ocean environment is inhospitable, preventing them from spreading into habitats similar to their own but located elsewhere. Distances separating such habitats might be too long to overcome either through their active swimming abilities or passive floating in water currents. Mechanisms by which humanity aids introduction of exotic species are called vectors of introduction and these are chiefly associated with shipment activities (hull fouling and ballast water) and marine aquaculture (Bax ''et al.'', 2003<ref name=Bax>Bax, N., Williamson, A., Aguero, M., Gonzalez, A. and Geeves, W. 2003. Marine invasive alien species: a threat to global biodiversity. Marine Policy 27: 313–323</ref>). Other vectors include ornamental species trade, the international transport and sale of live marine bait, live seafood, marine litter and live organisms for research and education.
  
 
* '''Shipment'''
 
* '''Shipment'''
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Organisms can travel either attached to the submerged part of the vessels hull or contained within their ballast waters. Ballast water has been extensively used since 1870s and certain species are able to complete their life cycle and breed in ballast waters, meaning that they can be translocated far away from their native range. Studies on ballast tanks found more than 1,000 taxa ranging from phytoplankton to small fish up to 15 cm in length (Gollash, 2004<ref> Gollash, S. (2004). A global perspective on shipping as a vector for new species introduction. Presented at the 13th International Conference on Aquatic Invasive Species, Ennis, Co Clare, Ireland 2004. Institute of Technology, Sligo.</ref>).
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Organisms can travel either attached to the submerged part of the vessels hull or contained within their [[Ballast water|ballast waters]]. Ballast water has been extensively used since 1870s and certain species are able to complete their life cycle and breed in ballast waters, meaning that they can be translocated far away from their native range. Studies on ballast tanks found more than thousand taxa ranging from phytoplankton to small fish up to 15 cm in length (Gollash ''et al.'', 2004<ref>Gollash, S. 2004. A global perspective on shipping as a vector for new species introduction. Presented at the 13th International Conference on Aquatic Invasive Species, Ennis, Co Clare, Ireland 2004. Institute of Technology, Sligo.</ref>).
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In order to combat the global dispersion of species, an international initiative was launched in 2004 for a Ballast Water Management Convention, which came into effect in 2017. Under the Convention, ships are required, according to a timetable of implementation, to comply with the D1 or D2 standards <ref>[https://www.imo.org/en/OurWork/Environment/Pages/BallastWaterManagement.aspx Ballast Water Management Convention]</ref>. The D1 standard requires ships to carry out a ballast water exchange, and specifies the volume of water that must be replaced. This standard involves exchanging the uptaken discharge water from the last port, with new sea water; it must occur at a minimum of 200 nautical miles from shore. The D2 standard is more stringent and requires the use of an approved ballast water treatment system. The main types of ballast water treatment technologies are <ref>[https://www.marineinsight.com/tech/how-ballast-water-treatment-system-works/ Ballast water treatment technologies]</ref>:
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Filtration systems (physical); Chemical disinfection (oxidizing and non-oxidizing biocides); Ultra-violet treatment; Deoxygenation treatment; Heat (thermal treatment); Acoustic (cavitation treatment); Electric pulse/pulse plasma systems; Magnetic Field Treatment. For further details, see the article [[Ballast water]].
  
 
* '''Mariculture'''
 
* '''Mariculture'''
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There has been a growing interest in the search for fish, shellfish, and plant species whose biology was well known and which either already had achieved or could achieve success in cultivation. Depending on the type of mariculture, the organisms can be either allowed to establish in the wilderness (intentional species introduction) or kept in enclosures from which they occasionally escape (accidental release) either directly or through their dispersal system. Very often those new introduced species carried along parasitic organisms that could later establish themselves in indigenous species. Since the latter have not developed any defence strategy against non-indigenous parasites, they could be greatly impacted.
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There has been a growing interest in the search for fish, shellfish, and plant species whose biology was well known and which either already had achieved or could achieve success in cultivation. Aquaculture is the world's fastest expanding food production sector, with an annual growth rate of 37% recorded in 2016 and a projected production of 109 million tonnes by 2030 (FAO, 2018<ref>FAO, 2018. The State of World Fisheries and Aquaculture 2018 - Meeting the Sustainable Development Goals. Rome. http://www.fao.org/3/i9540en/I9540EN.pdf.</ref>). Depending on the type of [[mariculture]], the organisms can be either allowed to establish in the wilderness (intentional species introduction) or kept in enclosures from which they occasionally escape. It is estimated that 26.5% of global fish farming comprises non-native species, equating 1.74 million tonnes per year and that nearly a third of marine ecoregions of the world are to some extent at risk from the impacts of fish escapes (Atalah and Sanchez-Perez, 2020<ref>Atalah, J. and Sanchez-Perez, P. 2020. Global assessment of ecological risks associated with farmed fish escapes. Global Ecology and Conservation 21, e00842</ref>). Escapees are the result of, among other things, net failures, storms and accidents at sea.  
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[[File:CaulerpaTaxifolia.jpg|thumb|left|300px|The invasive green algae ''Caulerpa taxifolia'' has come to cover 97% of available surfaces between Toulon and Genes (France, Monaco and Italy) in the 15 years since its discovery off Monaco, and has already been spread to the Adriatic Sea, and is projected to eventually spread over most of the Mediterranean<ref name=Bax/>. Photo credit Richard Ling <ref>[https://cisr.ucr.edu/invasive-species/caulerpa-taxifolia-or-killer-alga Caulerpa taxifolia, photo Richard Ling]</ref>].]]
 
* '''Ornamental species trade'''
 
* '''Ornamental species trade'''
 
Saltwater species are a rapidly growing sector of the aquarium industry. Species can be released by their owners either accidentally or deliberately when no longer wanted. This vector is responsible for one of the major invasions launched up to date, namely the release of ''Caulerpa taxifolia'' from Oceanographic Museum of Monaco.
 
Saltwater species are a rapidly growing sector of the aquarium industry. Species can be released by their owners either accidentally or deliberately when no longer wanted. This vector is responsible for one of the major invasions launched up to date, namely the release of ''Caulerpa taxifolia'' from Oceanographic Museum of Monaco.
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* '''Marine litter'''
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Floating litter in marine environments forms a substrate for marine organisms that can travel in this way over great distances. The most common phyla found on marine litter are Arthropoda (about 29 %), Mollusca (about 23 %), Bryozoa (about 19 %), Annelida (about 7 %) and Cnidaria (about 5 %) (Mghili et al. 2023<ref>Mghili, B., De-la-Torre, G.E. and Aksissou, M. 2023. Assessing the potential for the introduction and spread of alien species with marine litter. Marine Pollution Bulletin 191, 114913</ref>). Plastics, which enter the oceans in the millions of tons each year, provide many endemic species with a more efficient means of transportation than their natural dispersal mechanisms. Due to their buoyancy and persistence, plastic litter can spread widely across all ocean compartments and act as a primary vector for the introduction of alien species.
  
 
* '''Indirect introduction'''
 
* '''Indirect introduction'''
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Occasionally, species introduction can result not from their physical re-location but by offering a way for its dispersal to areas that it wouldn’t be able to reach if the conditions were not changed. Such opportunity is offered by alteration of hydrological regimes, like canal and reservoir construction (Grigorovich ''et al.'', 2002<ref> Grigorovich, I. A., MacIsaac H. J,. Shadrin, N. V., Mills, E. L., (2002). Patterns and mechanisms of aquatic invertebrate introductions in the Ponto-Caspian region. Canadian Journal of Fisheries and Aquatic Science 59: 1189-1208. </ref>).
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Occasionally, species introduction can result not from their physical re-location but by offering a way for its dispersal to areas that it wouldn’t be able to reach if the conditions were not changed. Such opportunity is offered by alteration of hydrological regimes, like canal and reservoir construction (Grigorovich ''et al.'', 2002<ref> Grigorovich, I. A., MacIsaac H. J,. Shadrin, N. V., Mills, E. L. 2002. Patterns and mechanisms of aquatic invertebrate introductions in the Ponto-Caspian region. Canadian Journal of Fisheries and Aquatic Science 59: 1189-1208. </ref>).
  
 
* '''Secondary introduction'''
 
* '''Secondary introduction'''
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If species are introduced and become established in a new geographic setting, they might continue to spread by both natural and anthropogenic mechanisms, colonizing habitats that they wouldn’t be able to reach without the initial, human-mediated translocation. Such introduction is termed a secondary introduction.
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If species are introduced and become established in a new geographic setting, they might continue to spread by both natural and anthropogenic mechanisms, colonizing [[habitat|habitats]] that they wouldn’t be able to reach without the initial, human-mediated translocation. Such introduction is termed a secondary introduction.
  
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Rarely we can connect an invasion event with one particular vector. Instead, it is more common to assess the probability of a given vector being responsible. In British waters accidental release associated with mariculture has been identified as the main vector with other important vectors being fouling, ballast water and deliberate commercial introduction (Eno ''et al.'', 1997<ref> Eno, N. C., Clark, R. A., Sanderson, W. G. (eds) 1997. Non-native marine species in British waters. Joint Nature Conservation Commission, Peterborough, UK.</ref>).
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Very rarely we can connect an invasion event with one particular vector. Instead it is more common to assess the probability of a given vector being responsible. In British waters accidental release associated with mariculture has been identified as the main vector with other important vectors being fouling, ballast water and deliberate commercial introduction (Eno ''et al.'', 1997<ref> Eno, N. C., Clark, R. A., Sanderson, W. G. (eds), (1997) Non-native marine species in British waters. Joint Nature Conservation Commission, Peterborough, UK.</ref>).
 
  
 
== From establishment to invasion ==
 
== From establishment to invasion ==
  
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Not all translocated species become established in new environments. If the population is relatively small it will be vulnerable to stochastic threats such as demographic or genetic drift. It is hard to predict what is the minimum viable population size. A generally accepted rule is that 50 individuals are needed to prevent excessive inbreeding and a minimum population of 500 hundred is required to keep a sufficiently high level of heterozigosity (Franklin 1980<ref> Franklin, I. R. (1980) Evolutionary change in small populations. In M. E. Soulé and B. A. Wilcox (eds) Conservation Biology: An Evolutionary-Ecological Perspective, pp. 135-39. Sinauer Associates Sunderland, Massachusetts. </ref>). Yet, those numbers may very greatly between different taxa and even if the population is large enough to prevent loss of alleles, it still might be prone to environmental threats such as poor food or oxygen availability, impacting recruitment success or juveniles development, or catastrophic events (El Niño, tsunami, etc.)
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Not all translocated species become '''established''' in new environments. There are barriers that need to be overcome by a species or population, such as the abiotic conditions of the recipient environment, particularly salinity and temperature. This limits the establishment of introduced species to conditions approximating their native ranges. If the translocated population is relatively small it will be vulnerable to stochastic threats such as demographic or genetic drift. It is hard to predict what is the minimum viable population size. A generally accepted rule is that 50 individuals are needed to prevent excessive inbreeding and a minimum population of 500 hundred is required to keep a sufficiently high level of heterozigosity (Franklin 1980<ref> Franklin, I. R. 1980. Evolutionary change in small populations. In M. E. Soulé and B. A. Wilcox (eds) Conservation Biology: An Evolutionary-Ecological Perspective, pp. 135-39. Sinauer Associates Sunderland, Massachusetts. </ref>). Yet, those numbers may very greatly between different taxa and even if the population is large enough to prevent loss of alleles, it still might be prone to environmental threats such as poor food or oxygen availability, impacting [[recruitment]] success or juveniles development, or catastrophic events (El Niño, [[tsunami]], etc.)
  
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If the founder population is large enough to overcome stochastic threats and manages to establish itself in a new environment, it will join the network of interactions within the receiving environment. Alien species have evolved in different environments and it is hard to predict what their interactions with indigenous biota will be. Not all introduced species can be termed as invasive. Some of them may well coexist with native species and share the resources. But every now and then an introduced species becomes an invader and impacts the host community, with the ultimate result being eradication of native species and destabilization of the system.
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If the founder population is large enough to overcome stochastic threats and manages to establish itself in a new environment, it will join the '''network of interactions''' within the receiving environment. Alien species have evolved in different environments and it is hard to predict what their interactions with indigenous biota will be. Not all introduced species can be termed as invasive. Some of them may well coexist with native species and share the resources. But every now and then an introduced species becomes an '''invader''' and impacts the host community, with the ultimate result being destabilization of the system and possibly extinction of native species. Non-native species have been found to be a primary driver of both animal and plant extinctions, playing a role in 25% of plant extinctions and 33% of animal extinctions (Blackburn et al. 2019<ref>Blackburn, T.M., Bellard, C. and Ricciardi, A. 2019. Alien versus native species as drivers of recent extinctions. Front. Ecol. Environ. 17: 203-207</ref>).
  
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Organisms have been carried around hidden in dry ballast, attached to hulls or buried inside them for millennia and it is very likely that what we now consider cosmopolitan species are simply '''early introductions''' and that species such as ship-boring isopod (''Sphaeroma terebrans''), Asian seasquirt (''Stylea plicata''), giant kelp (''Macrocystis pyrifera''), mussels (''Mytilus galloprovincialis'' and ''Mytilus edulis'') and European periwinkle (''Littorina litorea'') can be early introductions (Carlton, 1999<ref> Carlton, J. T. 1999. Quo vadimus exotica oceanica? Marine bioinvasion ecology in the twenty-first century.  In Pederson,. J. (ed.), Marine Bioinvasions: Proceedings of the First National Conference, January 1999. Massachusetts Institute of Technology, Cambridge. </ref>). This in turn raises the issue of naturalisation: How much time is needed to fully incorporate a population in a community and bring the latter to equilibrium? How many interactions have to be established to call an introduced species integrated? Carlton also questioned the quality of our understanding of present marine communities. If we assumed a rather timid scenario that in the period 1500-1800 only three species were introduced elsewhere each year, we would have ended up with a number of thousand species that might have spread before humanity gained a general knowledge of biogeography, taxonomy and ecology. As a result, these species can be today considered as cosmopolitan. It might have a great impact on our understanding of marine ecology and community equilibrium in particular.
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Organisms have been carried around hidden in dry ballast, attached to hulls or buried inside them for millennia and it is very likely that what we now consider cosmopolitan species are simply early introductions and that species such as ship-boring isopod (''Sphaeroma terebrans''), Asian seasquirt (''Stylea plicata''), giant kelp (''Macrocystis pyrifera''), mussels (Mytilus galloprovincialis and ''Mytilus edulis'') and European periwinkle (''Littorina litorea'') can be possible early introductions (Carlton, 1999<ref> Carlton, J. T. (1999). Quo vadimus exotica oceanica? Marine bioinvasion ecology in the twenty-first century.  In Pederson,. J. (ed.), Marine Bioinvasions: Proceedings of the First National Conference, January 24-27, 1999. Massachusetts Institute of Technology, Cambridge. </ref>). This in turn raises the issue of naturalisation: How much time is needed to fully incorporate a population in a community and bring the latter to equilibrium? How many interactions have to be established to call an introduced species integrated? Carlton also questioned the quality of our understanding of present marine communities. If we assumed a rather timid scenario that between 1,500 and 1,800 only three species were introduced elsewhere each year, we would have ended up with a number of 1,000 species that might have spread before humanity gained a general knowledge of biogeography, taxonomy and ecology. As a result, these species can be today considered as cosmopolitan. It might have a great impact on our understanding of marine ecology and community equilibrium in particular.
 
  
 
== Impacts ==
 
== Impacts ==
  
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[[Image:Didemnum sp.jpg|right|thumb|200px|caption|Introduced colonial sea squirt (''Didemnum'' sp.) overgrowing the blue mussel ''Mytilus edulis'' in Irish Sea]]
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[[Image:Didemnum sp.jpg|right|thumb|300px|caption|Introduced colonial sea squirt (''Didemnum'' sp.) fouling other organisms, including the commercially important blue mussel ''Mytilus edulis'' in Irish Sea. (Photograph taken by Mr. Tom Ohman)]]
  
 
* '''Competition'''
 
* '''Competition'''
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Introduced species might have evolved in the presence of much more aggressive competitors than the ones present in the receiving environment and they might be extremely successful in colonising new areas. The most common competition is for resources, whether it is food, solar energy or space. In California bay the native shore crab (''Hemigrapsus oregonensis'') declined in mean abundance by 10 times as a consequence of the European green crab (''Carcinus maenas'') introduction and competition for food (''Nutricola'' sp.) (Grosholz ''et al.'', 2000<ref> Grosholz, E. D., Ruiz, G. M., Dean, C. A., Shirley, K. A., Maron, J. L. & Connors, P. G. (2000). The Impacts of a Non-indigenous Marine Predator in a California Bay, Ecology 81, 1206–1224. </ref>).
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Introduced species might have evolved in the presence of much more aggressive competitors than the ones present in the receiving environment and they might be extremely successful in colonising new areas. The most common competition is for resources, whether it is food, solar energy or space. In California bay the native shore crab (''Hemigrapsus oregonensis'') declined in mean abundance by 10 times as a consequence of the European green crab (''Carcinus maenas'') introduction and competition for food (''Nutricola'' sp.) (Grosholz ''et al.'', 2000<ref> Grosholz, E. D., Ruiz, G. M., Dean, C. A., Shirley, K. A., Maron, J. L. and Connors, P. G. 2000. The Impacts of a Non-indigenous Marine Predator in a California Bay, Ecology 81: 1206–1224</ref>).
  
 
* '''Diffuse competition'''
 
* '''Diffuse competition'''
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The impact on native organisms can be greater through diffuse competition. A population might resist competition along one axis if the resource is plentiful, but its realised niche can virtually disappear in the presence of several species competing along many axes (Giller, 1984<ref> Giller, P. S. (1984) Community Structure and the Niche. Chapman and Hall, London. </ref>).
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The impact on native organisms can be greater through diffuse competition. A population might resist competition along one axis if the resource is plentiful, but its realised niche can virtually disappear in the presence of several species competing along many axes (Giller, 1984<ref> Giller, P. S. 1984. Community Structure and the Niche. Chapman and Hall, London</ref>).
  
 
* '''Positive indirect interactions'''
 
* '''Positive indirect interactions'''
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Even with a stable or decreasing rate of new introductions, it can be assumed that systems will become increasingly destabilized through positive indirect interactions and diffuse competition, as more and more interactions within the community become altered. Even early, non-invasive introductions may become a nuisance due to a change induced by another introduced species (Grosholz, 2005<ref> Grosholz, E. D. (2005) Recent biological invasion may hasten invasional meltdown by accelerating historical introductions. Proceedings of the National Academy of Sciences of the United States of America, 102 (4): 1088-1091. </ref>). It is possible for a new alien to transform an older exotic species into an invader.
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Even with a stable or decreasing rate of new introductions, it can be assumed that systems will become increasingly destabilized through positive indirect interactions and diffuse competition, as more and more interactions within the community become altered. Even early, non-invasive introductions may become a nuisance due to a change induced by another introduced species (Grosholz, 2005<ref> Grosholz, E. D. 2005. Recent biological invasion may hasten invasional meltdown by accelerating historical introductions. Proceedings of the National Academy of Sciences of the United States of America, 102(4): 1088-1091</ref>). It is possible for a new alien to transform an older exotic species into an invader.
  
 
* '''Predation and herbivory'''
 
* '''Predation and herbivory'''
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* '''Parasitism'''
 
* '''Parasitism'''
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Very often introduced organisms are accompanied by parasitic species. Mass transfer of large numbers of animals and plants without inspection, quarantine, or other management procedures has led to the simultaneous introduction of pathogenic or parasitic agents.  
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Very often introduced organisms are accompanied by parasitic species. Mass transfer of large numbers of animals and plants without inspection, quarantine, or other management procedures has led to the simultaneous introduction of pathogenic or parasitic agents. Fish escaped from maricultures may carry along parasitic organisms that could later establish themselves in indigenous species (Kent, 2000<ref>Kent, M.L. 2000. Marine netpen farming leads to infections with some unusual parasites. Int. J. Parasitol. 30: 321-326</ref>), especially when farmed and wild fish of the same or closely related species are in close vicinity (Arechavala-Lopez ''et al.'', 2013<ref>Arechavala-Lopez, P., Sanchez-Jerez, P., Bayle-Sempere, J.T., Uglem, I., Mladineo, I. 2013. Reared fish, farmed escapees and wild fish stocks – a triangle of pathogen transmission of concern to Mediterranean aquaculture management. Aquacult. Environ. Interact. 3: 153-161</ref>). Since the wild fish have not developed any defence strategy against non-indigenous parasites, they could be greatly impacted.  
  
 
* '''Genetic impact'''
 
* '''Genetic impact'''
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If transferred species are closely related to native counterparts, they may hybridise affecting the original gene pool. Introduced or hybridised individuals may prove to be more successful in mating than the indigenous organisms and the original genetic diversity might be lost.
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If transferred species are closely related to native counterparts, they may hybridise affecting the original gene pool. This can especially happen with escapees from fish farms (Bolstad ''et al.'', 2017<ref>Bolstad, G.H., Hindar, K., Robertsen, G., Jonsson, B., Saegrov, H., Diserud, O.H., Fiske, P., Jensen, A.J., Urdal, K., Naesje, T.F., Barlaup, B.T., Floro-Larsen, B., Lo, H., Niemela, E. and Karlsson, S. 2017. Gene flow from domesticated escapes alters the life history of wild Atlantic salmon. Nat. Ecol. Evol. 1, 0124</ref>). Introduced or hybridised individuals may prove to be more successful in mating than the indigenous organisms and the original genetic diversity might be lost. Most farmed fish have low genetic diversity as a result of selective breeding for favourable production traits over several generations. Thus, genetic introgression of farmed fish can result in alterations in the genetic composition, long-term loss of fitness, adaptability and reduced survival of wild fish populations (Miralles ''et al.'', 2016<ref>Miralles, L., Mrugala, A., Sanchez-Jerez, P., Juanes, F. and Garcia-Vazquez, E. 2016. Potential impact of Mediterranean aquaculture on the wild predatory bluefish. Mar. Coast. Fish. 8: 92-99</ref>).  
  
 
* '''Multiple negative interactions'''
 
* '''Multiple negative interactions'''
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Two species may interact with one another in a several ways. A species confronted by one-way interactions can compromise and trade-off one component of fitness for the sake of the survival. If it is forced to compromise too many components it may be pushed into an extinction vortex (Russel ''et al.'', 2004<ref> Russel, B.R., Mills M. D., Belk, M. C. (2004). Complex interactions between native and invasive fish: the simultaneous effects of multiple negative interactions. Presented at the 13th International Conference on Aquatic Invasive Species, Ennis, Co Clare, Ireland 2004. Institute of Technology, Sligo. </ref>).
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Two species may interact with one another in a several ways. A species confronted by one-way interactions can compromise and trade-off one component of fitness for the sake of the survival. If it is forced to compromise too many components it may be pushed into an extinction vortex (Russel ''et al.'', 2004<ref> Russel, B.R., Mills M. D., Belk, M. C. 2004. Complex interactions between native and invasive fish: the simultaneous effects of multiple negative interactions. Presented at the 13th International Conference on Aquatic Invasive Species, Ennis, Co Clare, Ireland 2004. Institute of Technology, Sligo. </ref>).
  
 
== The problem ==
 
== The problem ==
  
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[[Image:Comb_jelly_Mnemiopsis_leidyi.jpg|left|thumb|250px|caption|The comb jelly ''Mnemiopsis leidyi'' (native to western Atlantic) feeds on eggs and larvae of pelagic fish and caused a dramatic drop in fish populations in the Black Sea by competing for the same food sources and eating the young and eggs (Kube ''et al.'', 2007<ref>Kube, S., Postel, L., Honnef, C. and Augustin, C.B. 2007. Mnemiopsis leidyi in the Baltic Sea - distribution and overwintering between autumn 2006 and spring 2007. Aquatic Invasions 2(2): 137-145.</ref>) <ref>http://en.wikipedia.org/wiki/Mnemiopsis_leidyi#cite_note-kubeetal2007-4</ref>]]
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Over 100 non-native species have been recorded in the NE Atlantic, mainly in the North Sea, the Celtic Sea, the Bay of Biscay and along the Iberian coast. Impacts of invasive species vary in different regions and sometimes are rather localized. Over the past twenty years, the number of alien species transported into the Baltic has increased and poses a significant threat to the region given its naturally low species diversity. At least 50 non-native species have entered the Black Sea in the last century. Some have been invasive e.g. the comb jelly-fish ''Mnemiopsis leidyi'' was the primary cause of collapse of the fisheries in the area in the early 1990s.
 
  
−
Consequences of human-induced altering of species composition are sometimes detrimental to local communities and their magnitude may range from limitation or exclusion of single species or to destabilization of the whole system and species introduction has been identified as one of the main causes of species extinction. Even with a stable or decreasing rate of new introductions, it can be assumed that systems will become increasingly destabilized through direct and indirect interactions and diffuse competition as more and more interactions within the community become altered. In areas that have already been heavily invaded, reducing the numbers of new introductions may not be a sufficient strategy. In addition to preventing new introductions, it may be necessary to mitigate the impacts of exotic species that have already become established. Given the large number of alien species already present, there is a high potential for positive interactions to produce many future management problems.
+
Consequences of human-induced altering of species composition are sometimes detrimental to local communities and their magnitude may range from limitation or exclusion of single species or to destabilization of the whole system and species introduction has been identified as one of the main causes of species extinction. Even with a stable or decreasing rate of new introductions, it can be assumed that systems will become increasingly destabilized through direct and indirect interactions and diffuse competition as more and more interactions within the community become altered. In areas that have already been heavily invaded, reducing the numbers of new introductions may not be a sufficient strategy. In addition to preventing new introductions, it may be necessary to mitigate the impacts of exotic species that have already become established.  
  
 +
At least 50 non-native species have entered the Black Sea in the last century and some have been invasive. For instance, the comb jelly-fish ''Mnemiopsis leidyi'' was the primary cause of collapse of the fisheries in the area in the early 1990s. Over 100 non-native species have been recorded in the NE Atlantic, mainly in the [[North Sea]], the Celtic Sea, the Bay of Biscay and along the Iberian coast. Impacts of invasive species vary in different regions and sometimes are rather localized. Over the past twenty years, the number of alien species transported into the [[Baltic Sea|Baltic]] has increased and poses a significant threat to the region given its naturally low species diversity.
 +
In North America, some 300 non-indigenous species of invertebrates and [[algae]] have been established in marine and estuarine waters (Ruiz ''et al.'', 2000<ref> Ruiz, G.M., Fofonoff, P.W., Carlton, J.T., Wonham, M.J. and Hines, A.H. 2000. Invasions of coastal marine communities in North America: apparent patterns, processes, and biases. Annual Review of Ecology and Systematics 31: 481-531</ref>).
 +
The polyclad flatworms of the clade ''Postenterogonia orbicularis'' recently discovered in northern Spain and south-west France, is an invasive species that can enter bivalves when they filter and develop inside molluscs, making the management of the pest a real challenge for the aquaculture facilities<ref>Lopez-Alonso, R., Pascual-Parra, E., Gonzalez-Toral, C., del Cerro, A., Munoz, M., Soto-Lopez, V., Menendez-Telena, D., Carrera-Rodriguez, I., García-Maza, J.A., Cires, E. and Arias, A. 2025.  A new threat to the European marine environment: The exotic polyclad flatworm Postenterogonia orbicularis (Schmarda, 1859). Regional Studies in Marine Science 78, 103758</ref>. Rates of invasion among most microscopic organisms such as bacteria are still unreported and it appears that their potential of dispersal by human-mediated vector is very significant<ref>Mallon, C. A., Elsas, J. D. V. and Salles, J. F. 2015. Microbial Invasions: The process, patterns, and mechanisms. Trends in Microbiology, 23: 719-729</ref>.
  
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International Maritime Organization has compiled a list of the most unwanted marine invaders on a global scale. They are as follows:
 
  
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<u>Cholera</u> (''Vibrio cholerae'') – various strains
+
==Policy==
−
Native to: various strains with broad ranges.
+
The issue of non-native species invasions is dealt with in the European Water Framework Directive (WFD) and the European Marine Strategy Framework Directive (MSFD). Following the MSFD<ref> Directive 2008/56/EC of the European Parliament and of the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive) https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex%3A32008L0056 </ref>, European member states are required to report on the environmental status of the European marine regions following descriptors of Good Environmental Status (GES), including the Descriptor D2: "Non-indigenous species introduced by human activities are at levels that do not adversely alter the ecosystem" (MSFD 2021 <ref>Marine Strategy Framework Directive – Descriptor 2, Non-Indigenous Species. Publications Office of the European Union JRC124136. https://publications.jrc.ec.europa.eu/repository/handle/JRC124136 </ref>). The reporting includes regular inventories on non-native invasive species, their new distribution ranges as well as the temporal introduction trend. Information should also be provided on identified introduction pathways and on measures to prevent and combat non-native species invasions (article 13 of the MSFD).
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Introduced to: South America, Gulf of Mexico and other areas.
 
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Impact: Some cholera epidemics appear to be directly associated with ballast water.
 
  
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<u>Cladoceran water flea</u> (''Cercopagis pengoi'')
+
In the United States, numerous federal and interagency efforts share responsibilities regarding invasive species. Among the federal agencies involved are the Departments of Agriculture, Commerce, Defense, Homeland Security, Interior, Transportation, and others, including the Environmental Protection Agency and the Executive Office of the President. Of these, three Departments—Agriculture, Commerce, and Interior—play a major role by co-chairing the National Invasive Species Council (NISC). Created by Executive Order 13112 in 1999, NISC provides high-level interdepartmental coordination of federal invasive species actions and works with other federal and nonfederal groups to address invasive species issues at the national level. The USA policy on invasive species management aims to manage the risk of invasive species in their activities, and minimize that risk where applicable and practicable, in cooperation with others as appropriate. This includes helping prevent the introduction, establishment, and spread of invasive species; promoting early detection and rapid response; and providing for eradication and control to minimize adverse impacts, such as impacts to the environment, human health and safety, cultural resources, recreation, infrastructure, and the economy<ref>Department of the Interior, Departmental Manual 2020. Environmental Quality Programs, part 524: Invasive Species Management.  https://www.doi.gov/sites/doi.gov/files/elips/documents/524-dm-1-508.pdf</ref>.
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Native to: Black and Caspian Sea.
 
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Introduced to: Baltic Sea.
 
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Impact: Reproduces to form very large populations that dominate the zooplankton
 
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community and clog fishing nets and trawls, with associated economic impacts.
 
  
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<u>Mitten crab</u> (''Eriocheir sinensis'')
+
International measures to control the dispersal of species outside their natural habitat are mainly targeting ship ballast water, see the article [[Ballast water]]. Since global shipping is the most common pathway for invasions of alien species, ports are suitable places for early detection.
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Native to: Northern Asia.
 
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Introduced to: Western Europe, Baltic Sea, west coast of North America.
 
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Impact: Undergoes mass migrations for reproductive purposes. Burrows into river banks
 
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and dykes causing erosion and siltation. Preys on native fish and invertebrate species, causing local extinctions during population outbreaks. Interferes with fishing activities
 
  
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<u>Toxic algae</u>  – various species
 
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Native to: Various species with broad ranges.
 
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Introduced to: Various areas.
 
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Impact: May form harmful algae blooms. Depending on the species, can cause massive
 
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kills of marine life through oxygen depletion, release of toxins and/or mucus. Can foul beaches and impact on tourism and recreation. Some species may contaminate filter-feeding shellfish and cause fisheries to be closed. Consumption of contaminated shellfish by humans may cause severe illness and death.
 
  
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<u>Round goby</u> (''Neogobius melanostomus'')
 
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Native to: Black, Azov and Caspian Sea.
 
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Introduced to: Baltic Sea and North America.
 
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Impact: Highly adaptable and invasive. Increases in numbers and spreads quickly. Spawns multiple times per season and survives in poor water quality. Competes for food and habitat with native fish including commercially important species, and preys on their eggs and young.
 
  
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<u>North American comb jelly</u> (''Mnemiopsis leidyi'')
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==Related articles==
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Native to: Eastern seaboard of the Americas.
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:[[Invading species in the Baltic Sea]]
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Introduced to: Black, Azov and Caspian Sea.
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:[[Threats to the coastal zone]]
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Impact: Reproduces rapidly (self fertilising hermaphrodite) under favourable conditions.
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:[[Ballast water]]
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Feeds excessively on zooplankton. Depletes zooplankton stocks; altering food web and ecosystem function. Contributed significantly to collapse of Black and Azov Sea fisheries in 1990s, with massive economic and social impact. Threatens similar impact in Caspian Sea.
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:[[Species extinction]]
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:[[Ecological thresholds and regime shifts]]
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:[[Resilience and resistance]]
  
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<u>North Pacific sea star</u> (''Asterias amurensis'')
 
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Native to: Northern Pacific.
 
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Introduced to: Southern Australia.
 
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Impact: Reproduces in large numbers, reaching 'plague' proportions rapidly in invaded
 
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environments. Feeds on shellfish, including commercially valuable scallop, oyster and clam species.
 
  
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<u>Zebra Mussel</u> (''Dreissena polymorpha'')
 
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Native to: Eastern Europe (Black Sea).
 
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Introduced to: Western and northern Europe, eastern half of North America.
 
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Impact: Fouls all available hard surfaces in mass numbers in freshwater and estuarine waters. Displaces native aquatic life.
 
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Alters habitats, ecosystems and food webs. Causes severe fouling problems on infrastructure and vessels. Blocks water intake pipes, sluices and irrigation ditches. Economic costs to USA alone of around US$750 million to $1 billion between 1989 and 2000.
 
  
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<u>Asian kelp</u> (''Undaria pinnatifida'')
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== External websites ==
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Native to: Northern Asia.
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* [http://www.cbd.int/invasive/doc/marine-menace-iucn-en.pdf Marine invasive species]
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Introduced to: Southern Australia, New Zealand, west coast of the United States, Europe
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* IMO Ballast Water Treatment R&D Directory http://globallast.imo.org/index.asp?page=bwprojects.htm
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and Argentina.
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* Baltic Sea Alien Species Database http://www.corpi.ku.lt/nemo/intro_contents.html
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Impact: Grows and spreads rapidly, both vegetatively and through dispersal of spores.  
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* International Conference on Aquatic Invasive Species http://www.icais.org/
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Displaces native algae and marine life. Alters habitats, ecosystems and food webs.  
 
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May affect commercial shellfish stocks through space competition and alteration of habitat.
 
  
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<u>European green crab</u> (''Carcinus maenas'')
 
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Native to: European Atlantic coast.
 
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Introduced to:  Southern Australia, south Africa, the U.S.A. and Japan.
 
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Impact: Highly adaptable and invasive. Resistant to predation due to hard shell.
 
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Competes with and displaces native crabs and becomes a dominant species in invaded areas. Consumes and depletes wide range of prey species. Alters inter-tidal rocky shore ecosystems.
 
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Rates of invasion among most microscopic organisms such as bacteria are still unreported and it appears that their potential of dispersal by human-mediated vector is very significant.
 
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== Further reading ==
 
  
 
== References ==
 
== References ==
 
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<references/>
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[[Category:Coastal and marine ecosystems]]
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[[Category:Marine Biodiversity‏‎]]

Latest revision as of 16:19, 29 October 2024

The introduction of non-native organisms (also called 'alien species') to new marine environments is believed to be one of the greatest threats to the world's marine biodiversity. Together with overexploitation, it has been identified as the major cause of species extinction (Bellard et al., 2016[1]). An alien or non-native species is one that has been intentionally or accidentally transported and released into an environment outside of its historic or resident geographical range or habitat. Such species are described as 'invasive' if they strongly disturb the ecosystem of the new marine environment, with possibly negative economic consequences. Invasive species can profoundly alter the structure and function of marine ecosystems by changing biodiversity and eliminating vital components of the food chain.


Functional integrity of species communities

Even though all seas are interconnected, there are certain dispersion barriers such as salinity, temperature gradient or ocean currents that keep local communities distinct. Two identical habitats can have different species communities with different types of interactions contributing to the global richness of biodiversity. Indigenous, or native species are those living within their natural range (past or present) including the area that it can reach and occupy using its natural dispersal system. By contrast, introduced species are transported most often accidentally and sometimes intentionally by human-mediated vectors into habitats outside their native range. These species are also termed as alien, exotic, invasive, foreign, non-native, immigrant, neobiota, naturalized, or non-indigenous. Some biota cannot be sufficiently proved to be neither native nor exotic and these are termed cryptogenic species (Carlton, 1996 [2])

Through the evolutionary fitness processes, species adjust to each other and adapt to available resources by occupying different ecological niches within communities. Virtually all resources are utilized optimally and all available niches are filled, maximising the biodiversity value. Various factors influence the functional integrity of a community. If changes are occurring gradually over a long timescale species have enough time to adapt and fill available niches. In turn more rapid shifts create niche openings and this has been identified as the main prerequisite of species invasion. Non-native species are found primarily in disturbed areas, such as harbours, bays, estuaries and semi-enclosed seas where the communities are weakened by various types of pollution (Elton, 1958[3]; Cohen, 2004[4]).

Vectors of introduction

Whether deliberately or accidentally, people have been transporting whole range of organisms, breaking natural distribution boundaries and interfering with community structures. The unwanted hitchhikers are usually either well-hidden or too small to be noticed – for the entire lifespan or just for its part.

For most coastal species the open ocean environment is inhospitable, preventing them from spreading into habitats similar to their own but located elsewhere. Distances separating such habitats might be too long to overcome either through their active swimming abilities or passive floating in water currents. Mechanisms by which humanity aids introduction of exotic species are called vectors of introduction and these are chiefly associated with shipment activities (hull fouling and ballast water) and marine aquaculture (Bax et al., 2003[5]). Other vectors include ornamental species trade, the international transport and sale of live marine bait, live seafood, marine litter and live organisms for research and education.

  • Shipment

Organisms can travel either attached to the submerged part of the vessels hull or contained within their ballast waters. Ballast water has been extensively used since 1870s and certain species are able to complete their life cycle and breed in ballast waters, meaning that they can be translocated far away from their native range. Studies on ballast tanks found more than thousand taxa ranging from phytoplankton to small fish up to 15 cm in length (Gollash et al., 2004[6]).

In order to combat the global dispersion of species, an international initiative was launched in 2004 for a Ballast Water Management Convention, which came into effect in 2017. Under the Convention, ships are required, according to a timetable of implementation, to comply with the D1 or D2 standards [7]. The D1 standard requires ships to carry out a ballast water exchange, and specifies the volume of water that must be replaced. This standard involves exchanging the uptaken discharge water from the last port, with new sea water; it must occur at a minimum of 200 nautical miles from shore. The D2 standard is more stringent and requires the use of an approved ballast water treatment system. The main types of ballast water treatment technologies are [8]: Filtration systems (physical); Chemical disinfection (oxidizing and non-oxidizing biocides); Ultra-violet treatment; Deoxygenation treatment; Heat (thermal treatment); Acoustic (cavitation treatment); Electric pulse/pulse plasma systems; Magnetic Field Treatment. For further details, see the article Ballast water.

  • Mariculture

There has been a growing interest in the search for fish, shellfish, and plant species whose biology was well known and which either already had achieved or could achieve success in cultivation. Aquaculture is the world's fastest expanding food production sector, with an annual growth rate of 37% recorded in 2016 and a projected production of 109 million tonnes by 2030 (FAO, 2018[9]). Depending on the type of mariculture, the organisms can be either allowed to establish in the wilderness (intentional species introduction) or kept in enclosures from which they occasionally escape. It is estimated that 26.5% of global fish farming comprises non-native species, equating 1.74 million tonnes per year and that nearly a third of marine ecoregions of the world are to some extent at risk from the impacts of fish escapes (Atalah and Sanchez-Perez, 2020[10]). Escapees are the result of, among other things, net failures, storms and accidents at sea.


The invasive green algae Caulerpa taxifolia has come to cover 97% of available surfaces between Toulon and Genes (France, Monaco and Italy) in the 15 years since its discovery off Monaco, and has already been spread to the Adriatic Sea, and is projected to eventually spread over most of the Mediterranean[5]. Photo credit Richard Ling [11]].
  • Ornamental species trade

Saltwater species are a rapidly growing sector of the aquarium industry. Species can be released by their owners either accidentally or deliberately when no longer wanted. This vector is responsible for one of the major invasions launched up to date, namely the release of Caulerpa taxifolia from Oceanographic Museum of Monaco.

  • Marine litter

Floating litter in marine environments forms a substrate for marine organisms that can travel in this way over great distances. The most common phyla found on marine litter are Arthropoda (about 29 %), Mollusca (about 23 %), Bryozoa (about 19 %), Annelida (about 7 %) and Cnidaria (about 5 %) (Mghili et al. 2023[12]). Plastics, which enter the oceans in the millions of tons each year, provide many endemic species with a more efficient means of transportation than their natural dispersal mechanisms. Due to their buoyancy and persistence, plastic litter can spread widely across all ocean compartments and act as a primary vector for the introduction of alien species.

  • Indirect introduction

Occasionally, species introduction can result not from their physical re-location but by offering a way for its dispersal to areas that it wouldn’t be able to reach if the conditions were not changed. Such opportunity is offered by alteration of hydrological regimes, like canal and reservoir construction (Grigorovich et al., 2002[13]).

  • Secondary introduction

If species are introduced and become established in a new geographic setting, they might continue to spread by both natural and anthropogenic mechanisms, colonizing habitats that they wouldn’t be able to reach without the initial, human-mediated translocation. Such introduction is termed a secondary introduction.

Rarely we can connect an invasion event with one particular vector. Instead, it is more common to assess the probability of a given vector being responsible. In British waters accidental release associated with mariculture has been identified as the main vector with other important vectors being fouling, ballast water and deliberate commercial introduction (Eno et al., 1997[14]).

From establishment to invasion

Not all translocated species become established in new environments. There are barriers that need to be overcome by a species or population, such as the abiotic conditions of the recipient environment, particularly salinity and temperature. This limits the establishment of introduced species to conditions approximating their native ranges. If the translocated population is relatively small it will be vulnerable to stochastic threats such as demographic or genetic drift. It is hard to predict what is the minimum viable population size. A generally accepted rule is that 50 individuals are needed to prevent excessive inbreeding and a minimum population of 500 hundred is required to keep a sufficiently high level of heterozigosity (Franklin 1980[15]). Yet, those numbers may very greatly between different taxa and even if the population is large enough to prevent loss of alleles, it still might be prone to environmental threats such as poor food or oxygen availability, impacting recruitment success or juveniles development, or catastrophic events (El Niño, tsunami, etc.)

If the founder population is large enough to overcome stochastic threats and manages to establish itself in a new environment, it will join the network of interactions within the receiving environment. Alien species have evolved in different environments and it is hard to predict what their interactions with indigenous biota will be. Not all introduced species can be termed as invasive. Some of them may well coexist with native species and share the resources. But every now and then an introduced species becomes an invader and impacts the host community, with the ultimate result being destabilization of the system and possibly extinction of native species. Non-native species have been found to be a primary driver of both animal and plant extinctions, playing a role in 25% of plant extinctions and 33% of animal extinctions (Blackburn et al. 2019[16]).

Organisms have been carried around hidden in dry ballast, attached to hulls or buried inside them for millennia and it is very likely that what we now consider cosmopolitan species are simply early introductions and that species such as ship-boring isopod (Sphaeroma terebrans), Asian seasquirt (Stylea plicata), giant kelp (Macrocystis pyrifera), mussels (Mytilus galloprovincialis and Mytilus edulis) and European periwinkle (Littorina litorea) can be early introductions (Carlton, 1999[17]). This in turn raises the issue of naturalisation: How much time is needed to fully incorporate a population in a community and bring the latter to equilibrium? How many interactions have to be established to call an introduced species integrated? Carlton also questioned the quality of our understanding of present marine communities. If we assumed a rather timid scenario that in the period 1500-1800 only three species were introduced elsewhere each year, we would have ended up with a number of thousand species that might have spread before humanity gained a general knowledge of biogeography, taxonomy and ecology. As a result, these species can be today considered as cosmopolitan. It might have a great impact on our understanding of marine ecology and community equilibrium in particular.

Impacts

Introduced colonial sea squirt (Didemnum sp.) fouling other organisms, including the commercially important blue mussel Mytilus edulis in Irish Sea. (Photograph taken by Mr. Tom Ohman)
  • Competition

Introduced species might have evolved in the presence of much more aggressive competitors than the ones present in the receiving environment and they might be extremely successful in colonising new areas. The most common competition is for resources, whether it is food, solar energy or space. In California bay the native shore crab (Hemigrapsus oregonensis) declined in mean abundance by 10 times as a consequence of the European green crab (Carcinus maenas) introduction and competition for food (Nutricola sp.) (Grosholz et al., 2000[18]).

  • Diffuse competition

The impact on native organisms can be greater through diffuse competition. A population might resist competition along one axis if the resource is plentiful, but its realised niche can virtually disappear in the presence of several species competing along many axes (Giller, 1984[19]).

  • Positive indirect interactions

Even with a stable or decreasing rate of new introductions, it can be assumed that systems will become increasingly destabilized through positive indirect interactions and diffuse competition, as more and more interactions within the community become altered. Even early, non-invasive introductions may become a nuisance due to a change induced by another introduced species (Grosholz, 2005[20]). It is possible for a new alien to transform an older exotic species into an invader.

  • Predation and herbivory

Some organisms are more effective competitors for resources than others and have the potential to dominate the area, excluding other species from the access to viable resources. In such cases organisms feeding on it (predators or herbivores) act as a biocontrol agent keeping their abundance low and maintain a high level of stability and productivity. If those predators or herbivores are introduced to a new environment, local community members might be lacking the evolutionary-driven ability to resist them. On the other hand if a species limited in number in its native range by biocontrol agents is introduced to a new environment, it might thrive and outcompete indigenous species.

  • Parasitism

Very often introduced organisms are accompanied by parasitic species. Mass transfer of large numbers of animals and plants without inspection, quarantine, or other management procedures has led to the simultaneous introduction of pathogenic or parasitic agents. Fish escaped from maricultures may carry along parasitic organisms that could later establish themselves in indigenous species (Kent, 2000[21]), especially when farmed and wild fish of the same or closely related species are in close vicinity (Arechavala-Lopez et al., 2013[22]). Since the wild fish have not developed any defence strategy against non-indigenous parasites, they could be greatly impacted.

  • Genetic impact

If transferred species are closely related to native counterparts, they may hybridise affecting the original gene pool. This can especially happen with escapees from fish farms (Bolstad et al., 2017[23]). Introduced or hybridised individuals may prove to be more successful in mating than the indigenous organisms and the original genetic diversity might be lost. Most farmed fish have low genetic diversity as a result of selective breeding for favourable production traits over several generations. Thus, genetic introgression of farmed fish can result in alterations in the genetic composition, long-term loss of fitness, adaptability and reduced survival of wild fish populations (Miralles et al., 2016[24]).

  • Multiple negative interactions

Two species may interact with one another in a several ways. A species confronted by one-way interactions can compromise and trade-off one component of fitness for the sake of the survival. If it is forced to compromise too many components it may be pushed into an extinction vortex (Russel et al., 2004[25]).

The problem

The comb jelly Mnemiopsis leidyi (native to western Atlantic) feeds on eggs and larvae of pelagic fish and caused a dramatic drop in fish populations in the Black Sea by competing for the same food sources and eating the young and eggs (Kube et al., 2007[26]) [27]

Consequences of human-induced altering of species composition are sometimes detrimental to local communities and their magnitude may range from limitation or exclusion of single species or to destabilization of the whole system and species introduction has been identified as one of the main causes of species extinction. Even with a stable or decreasing rate of new introductions, it can be assumed that systems will become increasingly destabilized through direct and indirect interactions and diffuse competition as more and more interactions within the community become altered. In areas that have already been heavily invaded, reducing the numbers of new introductions may not be a sufficient strategy. In addition to preventing new introductions, it may be necessary to mitigate the impacts of exotic species that have already become established.

At least 50 non-native species have entered the Black Sea in the last century and some have been invasive. For instance, the comb jelly-fish Mnemiopsis leidyi was the primary cause of collapse of the fisheries in the area in the early 1990s. Over 100 non-native species have been recorded in the NE Atlantic, mainly in the North Sea, the Celtic Sea, the Bay of Biscay and along the Iberian coast. Impacts of invasive species vary in different regions and sometimes are rather localized. Over the past twenty years, the number of alien species transported into the Baltic has increased and poses a significant threat to the region given its naturally low species diversity. In North America, some 300 non-indigenous species of invertebrates and algae have been established in marine and estuarine waters (Ruiz et al., 2000[28]). The polyclad flatworms of the clade Postenterogonia orbicularis recently discovered in northern Spain and south-west France, is an invasive species that can enter bivalves when they filter and develop inside molluscs, making the management of the pest a real challenge for the aquaculture facilities[29]. Rates of invasion among most microscopic organisms such as bacteria are still unreported and it appears that their potential of dispersal by human-mediated vector is very significant[30].


Policy

The issue of non-native species invasions is dealt with in the European Water Framework Directive (WFD) and the European Marine Strategy Framework Directive (MSFD). Following the MSFD[31], European member states are required to report on the environmental status of the European marine regions following descriptors of Good Environmental Status (GES), including the Descriptor D2: "Non-indigenous species introduced by human activities are at levels that do not adversely alter the ecosystem" (MSFD 2021 [32]). The reporting includes regular inventories on non-native invasive species, their new distribution ranges as well as the temporal introduction trend. Information should also be provided on identified introduction pathways and on measures to prevent and combat non-native species invasions (article 13 of the MSFD).

In the United States, numerous federal and interagency efforts share responsibilities regarding invasive species. Among the federal agencies involved are the Departments of Agriculture, Commerce, Defense, Homeland Security, Interior, Transportation, and others, including the Environmental Protection Agency and the Executive Office of the President. Of these, three Departments—Agriculture, Commerce, and Interior—play a major role by co-chairing the National Invasive Species Council (NISC). Created by Executive Order 13112 in 1999, NISC provides high-level interdepartmental coordination of federal invasive species actions and works with other federal and nonfederal groups to address invasive species issues at the national level. The USA policy on invasive species management aims to manage the risk of invasive species in their activities, and minimize that risk where applicable and practicable, in cooperation with others as appropriate. This includes helping prevent the introduction, establishment, and spread of invasive species; promoting early detection and rapid response; and providing for eradication and control to minimize adverse impacts, such as impacts to the environment, human health and safety, cultural resources, recreation, infrastructure, and the economy[33].

International measures to control the dispersal of species outside their natural habitat are mainly targeting ship ballast water, see the article Ballast water. Since global shipping is the most common pathway for invasions of alien species, ports are suitable places for early detection.


Related articles

Invading species in the Baltic Sea
Threats to the coastal zone
Ballast water
Species extinction
Ecological thresholds and regime shifts
Resilience and resistance


External websites


References

  1. ↑ Bellard, C., Cassey, P., Blackburn, T.M., 2016. Alien species as a driver of recent extinctions. Biol. Lett. 12, 20150623. https://doi.org/10.1098/rsbl.2015.0623
  2. ↑ Carlton, J.T. 1996. Biological invasions and cryptogenic species. Ecology 77(6): 1653-1655.
  3. ↑ Elton, C. S. 1958. The Ecology of Invasions by Animals and Plants, Methuen, London.
  4. ↑ Cohen, A. N. 2004. Invasion in the sea. In: Park Science vol. 22(2): 37-41
  5. ↑ 5.0 5.1 Bax, N., Williamson, A., Aguero, M., Gonzalez, A. and Geeves, W. 2003. Marine invasive alien species: a threat to global biodiversity. Marine Policy 27: 313–323
  6. ↑ Gollash, S. 2004. A global perspective on shipping as a vector for new species introduction. Presented at the 13th International Conference on Aquatic Invasive Species, Ennis, Co Clare, Ireland 2004. Institute of Technology, Sligo.
  7. ↑ Ballast Water Management Convention
  8. ↑ Ballast water treatment technologies
  9. ↑ FAO, 2018. The State of World Fisheries and Aquaculture 2018 - Meeting the Sustainable Development Goals. Rome. http://www.fao.org/3/i9540en/I9540EN.pdf.
  10. ↑ Atalah, J. and Sanchez-Perez, P. 2020. Global assessment of ecological risks associated with farmed fish escapes. Global Ecology and Conservation 21, e00842
  11. ↑ Caulerpa taxifolia, photo Richard Ling
  12. ↑ Mghili, B., De-la-Torre, G.E. and Aksissou, M. 2023. Assessing the potential for the introduction and spread of alien species with marine litter. Marine Pollution Bulletin 191, 114913
  13. ↑ Grigorovich, I. A., MacIsaac H. J,. Shadrin, N. V., Mills, E. L. 2002. Patterns and mechanisms of aquatic invertebrate introductions in the Ponto-Caspian region. Canadian Journal of Fisheries and Aquatic Science 59: 1189-1208.
  14. ↑ Eno, N. C., Clark, R. A., Sanderson, W. G. (eds) 1997. Non-native marine species in British waters. Joint Nature Conservation Commission, Peterborough, UK.
  15. ↑ Franklin, I. R. 1980. Evolutionary change in small populations. In M. E. Soulé and B. A. Wilcox (eds) Conservation Biology: An Evolutionary-Ecological Perspective, pp. 135-39. Sinauer Associates Sunderland, Massachusetts.
  16. ↑ Blackburn, T.M., Bellard, C. and Ricciardi, A. 2019. Alien versus native species as drivers of recent extinctions. Front. Ecol. Environ. 17: 203-207
  17. ↑ Carlton, J. T. 1999. Quo vadimus exotica oceanica? Marine bioinvasion ecology in the twenty-first century. In Pederson,. J. (ed.), Marine Bioinvasions: Proceedings of the First National Conference, January 1999. Massachusetts Institute of Technology, Cambridge.
  18. ↑ Grosholz, E. D., Ruiz, G. M., Dean, C. A., Shirley, K. A., Maron, J. L. and Connors, P. G. 2000. The Impacts of a Non-indigenous Marine Predator in a California Bay, Ecology 81: 1206–1224
  19. ↑ Giller, P. S. 1984. Community Structure and the Niche. Chapman and Hall, London
  20. ↑ Grosholz, E. D. 2005. Recent biological invasion may hasten invasional meltdown by accelerating historical introductions. Proceedings of the National Academy of Sciences of the United States of America, 102(4): 1088-1091
  21. ↑ Kent, M.L. 2000. Marine netpen farming leads to infections with some unusual parasites. Int. J. Parasitol. 30: 321-326
  22. ↑ Arechavala-Lopez, P., Sanchez-Jerez, P., Bayle-Sempere, J.T., Uglem, I., Mladineo, I. 2013. Reared fish, farmed escapees and wild fish stocks – a triangle of pathogen transmission of concern to Mediterranean aquaculture management. Aquacult. Environ. Interact. 3: 153-161
  23. ↑ Bolstad, G.H., Hindar, K., Robertsen, G., Jonsson, B., Saegrov, H., Diserud, O.H., Fiske, P., Jensen, A.J., Urdal, K., Naesje, T.F., Barlaup, B.T., Floro-Larsen, B., Lo, H., Niemela, E. and Karlsson, S. 2017. Gene flow from domesticated escapes alters the life history of wild Atlantic salmon. Nat. Ecol. Evol. 1, 0124
  24. ↑ Miralles, L., Mrugala, A., Sanchez-Jerez, P., Juanes, F. and Garcia-Vazquez, E. 2016. Potential impact of Mediterranean aquaculture on the wild predatory bluefish. Mar. Coast. Fish. 8: 92-99
  25. ↑ Russel, B.R., Mills M. D., Belk, M. C. 2004. Complex interactions between native and invasive fish: the simultaneous effects of multiple negative interactions. Presented at the 13th International Conference on Aquatic Invasive Species, Ennis, Co Clare, Ireland 2004. Institute of Technology, Sligo.
  26. ↑ Kube, S., Postel, L., Honnef, C. and Augustin, C.B. 2007. Mnemiopsis leidyi in the Baltic Sea - distribution and overwintering between autumn 2006 and spring 2007. Aquatic Invasions 2(2): 137-145.
  27. ↑ http://en.wikipedia.org/wiki/Mnemiopsis_leidyi#cite_note-kubeetal2007-4
  28. ↑ Ruiz, G.M., Fofonoff, P.W., Carlton, J.T., Wonham, M.J. and Hines, A.H. 2000. Invasions of coastal marine communities in North America: apparent patterns, processes, and biases. Annual Review of Ecology and Systematics 31: 481-531
  29. ↑ Lopez-Alonso, R., Pascual-Parra, E., Gonzalez-Toral, C., del Cerro, A., Munoz, M., Soto-Lopez, V., Menendez-Telena, D., Carrera-Rodriguez, I., García-Maza, J.A., Cires, E. and Arias, A. 2025. A new threat to the European marine environment: The exotic polyclad flatworm Postenterogonia orbicularis (Schmarda, 1859). Regional Studies in Marine Science 78, 103758
  30. ↑ Mallon, C. A., Elsas, J. D. V. and Salles, J. F. 2015. Microbial Invasions: The process, patterns, and mechanisms. Trends in Microbiology, 23: 719-729
  31. ↑ Directive 2008/56/EC of the European Parliament and of the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive) https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex%3A32008L0056
  32. ↑ Marine Strategy Framework Directive – Descriptor 2, Non-Indigenous Species. Publications Office of the European Union JRC124136. https://publications.jrc.ec.europa.eu/repository/handle/JRC124136
  33. ↑ Department of the Interior, Departmental Manual 2020. Environmental Quality Programs, part 524: Invasive Species Management. https://www.doi.gov/sites/doi.gov/files/elips/documents/524-dm-1-508.pdf


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Citation: Penk, Marcin (2024): Non-native species invasions. Available from http://www.coastalwiki.org/wiki/Non-native_species_invasions [accessed on 24-11-2024]



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