Course:EOSC270/2021/Impacts of Invasive Species on Marine Ecosystems

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Introduction on Marine Invasive Species

What are Marine Invasive Species

Marine invasive species refers to non-native species inhabiting native environments due to natural or human factors (this wiki page focuses on human interferences only).

The lionfish (Pterois miles) has high dispersion capacity and has become an dangerous invasive species on the east coast of the United States and the Caribbean. Damaging the local fish population, native predators struggle to compete with them.

Many introduced species died out, but some species grew rapidly without predators and parasites in their native range and became invasive species[1]. Marine invasive species often have strong reproductive and dissemination capabilities[1]. Usually, invasive species use this feature to rapidly expand their populations in new habitats at low density[2].Marine invasive species may cause massive extinction of marine life, destroy biodiversity, and permanently change habitats through direct and indirect impacts.[1].Direct impacts include predation and competition with native species[3]. For example, invasive species may not have natural predators in their new environment, and may compete with native species for resources (such as food, light, and habitat). Indirect impacts include spreading diseases between native species. Invasive species usually come from places with high diversity and have pathogens or diseases that are not found within the range of native species[3].The consequences bring by marine invasive species can lead to huge economic impacts and fundamental damage to marine ecosystems.

Characteristics of the intrusive areas

Over 70% of the earth is covered by oceans and major oceans, with a coastline of over 1.6 million kilometers[4]. There are aquatic invasive species all over the world, with depths of varying degrees[2]. These species reach areas such as wetlands, streams, rivers, bays, and the coasts[4].

Total numbers of invasive species distributed per bay in California, America. A large number of invasive species have been introduced in all major port areas and bays in California.

Areas with frequent marine species invasions usually have higher introduction paths (ports and other transportation hubs), are often key locations for ornamental aquatic trade[5]. For example, a large number of invasive species have been introduced in all major port areas and bays in California[6]. The San Francisco Bay has the largest number of non-native species, followed by the Port of Los Angeles/Long Beach[6]. The San Francisco Bay has become a hot spot for invasion due to its large number of leisure cruises and commercial traffic, the history of oyster culture, and its proximity to highly urbanized areas[6].

How Pervasive are Marine Invasive Species?

The 2019 United Nations assessment report highlights the threats posed by invasions and alien species, which are one of the five main driving factors affecting global biodiversity[5]. Studies have shown that the speed of foreign organisms flowing in global ports, new estuaries and oceans is increasing dramatically[7].

In the six ports of the United States, Australia and New Zealand, invasive species are established every 32 to 85 weeks, and the rate of establishment seems to be increasing[7].Preliminary analysis shows that only 16% of marine ecological areas have not reported marine invasions, and this number may even be exaggerated due to underreporting[1].

Invasion methods and vectors under human interference

People living in coastal areas are picking up marine organisms on the beach for food.

Fisheries/ Aquaculture

People consciously introduce and breed marine organisms that can produce greater economic benefits, such as fish, shrimp, and shellfish[1]. Some organisms escape or are abandoned by humans and enter the natural sea area during the breeding process and are prone to become invasive species[2]. For example, China introduced Procambarus clarkii from Japan for food, fishing bait and pets[1]. Procambarus clarkii is often mixed with domestic crops (such as rice). The escaped individuals survived by digging a hole in the embankment[1].

Ornamental species

Aquariums often have a variety of introduced exotic species for viewing, the green algae introduced by California Aquarium from Adriatic Sea is an example of viewin species to invasive species.

Aquariums and other exotic species have been introduced into the natural environment due to consumer demand[1]. Mismanagement of exotic species being released to non-native environments may cause unintentional yet serious consequences. For example, the green algae introduced from the Adriatic Sea to the California Aquarium gradually became the dominant species by releasing spores into the local marine ecosystem and led to the mass extinction of indigenous marine plants[2].

A cargo ship is docking on the sea waiting to be unloaded. The fouling species and the movable species that may be related to it can be directly attached to the hull [2].When biofouling organisms fall from the hull structure to release larvae, they are introduced into a new environment[2].

Ship Transportation

The bottom of the ship carries foreign attached organisms[2]. Marine organisms are carried by ocean currents and their swimming ability, forming the basic pattern of the existing biota[2]. The world's oceans are subject to constraints such as continental barriers, water temperature, ocean currents, and flushing water forming their own unique indigenous communities, and these constraints have affected the further spread of native species[3].

The Panama Canal connects the Atlantic Ocean with the Pacific Ocean, using a man-made artificial waterway measuring 48 miles (77 km) [3]


Canals can connect different biogeographical[4]. After the expansion of the Panama Canal was completed in 2016, giant ships that had to dock at West Coast ports after crossing the Pacific Ocean in the past will be able to directly transport cargo to the Gulf of Mexico and East Coast ports[8].They may spread more exotic species. California, which has hosted giant ships from the Western Pacific for decades, has more marine invaders than the rest of the United States[6]. Many exotic species such as gobies, tunicates, and algae are competing wildly with native species[6].

Recreational boats

Recreational boats in Granville Island, BC, Canada.

Recreational boating can be said to be the most unregulated medium for the introduction and spread of marine invasive species[8]. Relatively low speed and long navigation distance of recreational boats makes them ideal carriers for fouling species, which have been considered as non-native species[8]. British Columbia (BC) has the largest boating community in Canada, with an estimated 400,000 boats[8].The proximity of Washington State and its connectivity with other coastal US states make the waters of British Columbia vulnerable to major international introductions of exotic species[8].

Summary of common vectors of marine invasive species due to human activities[9]
Invasive method Vector
Commercial shipping Ballast water,

Hull fouling

Recreational boating Hull fouling

And fisheries

Gear, stock, or food movement,

Discarded nets, floats, etc.

Dive practices Snorkeling and scuba gear
Drilling platforms Ballast water,

Hull fouling

Canals Movement of species through locks
Aquarium Industry Accidental or intentional release

The Impact of Invasive Species in Marine Ecosystems

The common feature of coastal ecological areas that are severely affected by invasive marine organisms is that they are only located in the temperate zone like North Atlantic and North Pacific.

Characteristics of Potential Regions

Through the analysis of the regional distribution of marine invasive species in the world marine ecosystem, it is clear that new species will replace or renew the local marine ecosystem in a certain area without becoming overly dominant. With globalization, there has been an advance of the movement of goods, people, and capital, and in which a lot of it has taken place in the oceans of the world. The increase of human activities is also more likely to be an increase in the chances for more movement between species across different areas. This can be seen in areas, such as trade and tourism. There is a total of 78% of the 232 coastal ecological zones in the world which have encountered an invasion of marine alien species [10].

It is difficult to determine the reasons for the different kinds of invasions, but there are some commonalities between them. For example, the common feature of coastal ecological areas that are severely affected by invasive marine organisms is that they are only located in the temperate zones like the North Atlantic and North Pacific [10], while the threat of alien species in tropical or cold zones is not very high. There is also the fact that in areas that have more shipping movements, there will be more opportunities for the invasive species to migrate into other areas.

Process Analysis of Marine Species Invasion

Human activity trajectory can be used as a medium for the dispersal of alien species, such as shipping, aquaculture, corridors and aquarium trade. Non-native species spread to new habitats by hull traffic in two ways: by attaching to the hull and being taken to a new habitat for reproduction or by the water flow from the cabin to achieve species exchange.

Human activity and the evolving trajectory of development can be used as a medium for the dispersal of alien species such as shipping, aquaculture, transportation corridors and the aquarium trade. One of the major forms is through hull traffic. Non-native species spread to new habitats by hull traffic in two ways: by attaching to the hull and being taken to a new habitat for reproduction or by the water flow from the cabin, which then achieves species exchange [11]. Aquaculture has cultivated target aquatic products and often unintentionally introduces their related organisms. If they are not investigated before transportation has started or made another movement, the plankton larvae of these alien species will begin to reproduce and develop locally [11]. Similarly, if the aquarium trade accidentally releases non-native organisms into the natural ecosystem, there is also a high probability of species invasion, even if that had not been done intentionally or if some precautions are taken.

Marine Invasive Species Examples

There are many examples of threatening marine invasive species introduced by human activities:

Zebra Mussels

Zebra Mussels

Zebra Mussels were found in Canada in the 1980s. Females have extremely high spawning rates, and the excessive numbers have greatly reduced the local algae and plankton[12].

Killer Algae

Killer Algae (Caulerpa taxifolia)

This green seaweed is native to the Indian Ocean and Pacific Ocean and escaped from public and private aquariums by transportation. It spreads widely in the Mediterranean, depriving the original marine life of food and habitat[12].

Sea Lamprey

Sea Lampreys

The appearance of the sea lamprey is highly similar to that of an eel, with a mouth similar to a sucker. It will lay eggs in rivers and streams during the spawning period. It is highly aggressive, so its invasion greatly reduces the reproduction of local fish[12].

Extent of the Problem: Marine Invasive Species

Invasive species are considered by the International Union for the Conservation of Nature (IUCN) to be the second greatest threat to biodiversity following habitat degradation and pose a serious threat to the resilience of marine ecosystems worldwide.

While many species introduced to non-native regions fail to establish, others may find conditions suitable to their survival and reproduction and go on to flourish—leaving a wide array of lasting impacts. Some may predate on native species, decimating populations and altering the natural food chain interactions. Others may compete for resources, dominate species niches, alter nutrient cycles, or “engineer” their habitats, influencing the distribution of suitable resources for native organisms[7][13]. Colonizing populations of invasive species may further limit the genetic diversity of the ecosystem, as they represent only a subset of their original population[14].

The impact of invasive species on their environment is thus context dependent, as the severity of a species influence will be contingent on many factors.

Global map showing the distribution of "harmful" marine invasive species. Harmful species were defined by Molnar et al. (2008) as species that disrupt the functioning of multiple native species or the wider ecosystem.

Measuring Ecosystem Changes

Synthesis of research on 329 marine invasive species has revealed the extent and scope of their distribution, impacts on biodiversity, and introduction pathways[7]. The severity of a species impact was determined by their ecological impact, geographic extent, invasive potential, and management difficulty[7]. The study revealed that only 14% of marine ecoregions globally are considered free from invasive species—a value that scientists consider “generous” due to lack of further research in key parts of the world[7]. Of the species studied, 57% were considered “harmful,” meaning that their impact included the disruption of multiple species or the wider ecosystem. The highest degree of invasion was observed in the temperate Northern Atlantic, with roughly 137 harmful invasive species, the temperate Northern Pacific, with 78 harmful invasive species, and the Eastern Indo-Pacific, with 34 harmful invasive species. While research on invasive species dominates for well-studied regions such as the coastal regions of the United States, Europe, and Australia[7], it is evident that invasive marine species are distributed globally and each present their own unique challenges to the functioning of local ecosystems.

British Columbia and the European Green Crab

Image of a European Green Crab, an invasive species that is currently a source of concern within marine ecosystems of British Columbia.

One example relevant to the coastal waters of British Columbia is the introduction of the European Green Crab, and their role in “habitat engineering” of eelgrass ecosystems. Juvenile European Green Crabs consume eelgrass directly, while older crabs shred eelgrass blades and dislodge plants by bioturbation while foraging for other prey. The damage to eelgrass by European green crab changes the habitat composition for other species, which can have negative consequences for the biodiversity that traditionally relies on the area, as well as the functionality of the eelgrass in carbon capture and filtering[13].

Large shipping vessels in Vancouver, British Columbia. The main means of dispersal for marine invasive species is by attachment to boats such as these.

Present Status

The transportation of marine invasive species has increased dramatically with globalization, as the main method of introduction is by attachment to shipping vessels. Scientists have correlated the magnitude of shipping activities with increases in risk of harmful invasive species[7]. While there is little global data quantifying the level and impact of marine invasive species prior to 2007, it is understood that rates of dispersal have increased significantly over the past century in accordance with the exponential rise in marine transport of goods.

Looking Forward

Once established, marine invasive species can prove difficult and even impossible to remove[15]. Careful monitoring and managing of invasive species will thus be crucial to the maintenance of local populations.

Looking forward, changing environmental conditions, increasing fishing pressures, and accelerating rates of global transport lead scientists to predict an increase in alien species biomass, with devastating cumulative effects[16]. Research has also suggested that coexisting anthropogenic impacts such as climate change, ocean acidification, and pollution may intensify the already critical ecological effects of marine invasive species[17]. For these reasons, reliable predictors for the effects of invasive species will also be necessary to the mitigation of impacts by both intervention and prevention strategies.

Local and Global Solutions to the Spread of Marine Invasive Species

Local Solutions


Figure 1. The asian kelp(Undaria pinnatifida) is native to Japan, Korea, and China. It has colonized from Monterey Bay to Santa Catalina Island.

Boats have been revealed as one of the sources of transportation of invasive marine wildlife. Without proper outer cleaning maintenance in boats, invasive marine species are able to attach themselves to the sides or the bottom of the boat.[18] Examples of known invasive species that travel through attachment to boats include asian kelp (see Fig 1) and serpulid tubeworms. The asian kelp grows quickly and overtakes space, harming the local ecosystem and shellfish industry. Stuck to boat hulls, serpulid tubeworms(Hydroides diramphus and H. elegans) can increase drag and damage antifouling paint on these vessels.[19] They may compete with native species for food and space as they thrive in warm waters. For individuals who move from one body of the water to the next, it is emphasized to clean additional equipment (ie. diving equipment, fishing equipment, paddles) as they could also be carriers of marine invasive species.[20] Remove and dispose all plants and mud attached to the boat into the trash. A homemade solution to clean the exterior of the boat includes roughly 1/11th chlorine bleach with 10/11th water. A slogan that can help remember this solution is “Clean, Drain, Dry.”


Learning how to recognize marine invasive species in local public aquatic environments and reporting where they are sighted can help with their removal. Many resources exist to further public awareness of invasive species. For example, the website of Invasive Species Council of BC has online resources for actions against invasive species. Nearby provincial or national park websites can offer phone numbers or an online form to account the sighting. In Canada, British Columbia’s government website offers their app or online form to report sightings of invasive species as well as a phone number for specifically sightings of mussels. When invasive species are found early and authorities respond as soon as possible, evidence shows a more successful management of marine invasion.[21]

Volunteer Opportunities

Nearby provincial or national park websites can offer invasive species walks, removal efforts, and conservations of specific species.[22] Half-day hikes can be offered where you learn to identify and report invasive species. For example, the USA provides National Invasive Species Awareness Week activities to raise awareness and identify solutions to local invasive species issues. With regards to conservation efforts, Madagascar provides volunteering in areas such as reef surveying, community education, and reef regeneration.[22]

Global Solutions

Shipment Management

Figure 2. Ballast Water is created when water is drawn from a ship’s surrounding environment. This water could contain non-native species.
Figure 3. Veined rapa whelk(Rapana venosa) is native to the Northwest Pacific and found in the Black Sea and Mediterranean Sea through ballast water.

Vessel owners and operators are tasked with finding ways to prevent transfer of marine invasive species such as the veined rapa whelk (see fig 3) and European green crab via the ballast water. A solution to ballast water is either a mechanical, physical, chemical or biological treatment onboard ship or offshore to destroy any organisms.[23] Another solution is to exchange these water for open-ocean water during the route to destination. Governments worldwide have implemented regulations to enforce management practices such as Canada called the “Ballast Water Control and Management Regulations.”  [23]

Figure 4. The striped barnacle(Amphibalanus amphitrite) is from the Southwestern Pacific and Indian Ocean and was brought to parts of Southern California by biofouling.

Vessel owners and operators are also tasked with reducing biofouling that carries invasive marine species such as the striped barnacle (see fig 4) and the burrowing Australasian isopod.[24] Biofouling is a process where live marine organisms attach themselves to the ships’ hulls. The striped barnacle can reduce speeds of ships by up to 40% and increase the use of fuel. The burrowing Australasian isopod creates holes in soft bay shores and causes some shoreline regions to retreat by a couple of yards. Solutions to this issue include marine growth prevention systems, regular hull cleaning, and using biofouling resistant materials. The International Maritime Organization recommends these solutions but does not enforce these practices to control biofouling.


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