List of aquatic invasive species in Nova Scotia

These aquatic invasive species have been seen in Nova Scotia. For each species, the following information is shown:

name
species type (biological category)
habitat type
- freshwater: lakes and rivers with little to no salt content
- marine: oceanic areas with high salt content
- terrestrial: on land. In this case, areas next to water.
known locations in Nova Scotia
- Distributions of freshwater species in the table are described with reference to counties, and marine species distributions reference marine subregions. Observation within a county or subregion does not mean the species is found throughout it.
- Note: the full distributions of aquatic invasive species are often unknown. A lack of observation within a particular area does not mean the species is absent from that area, just that it has not been observed there.
pathways of introduction and spread (how aquatic invasive species arrive or spread as a result of human activities)
- If multiple pathways are listed, an asterisk (*) indicates likely mode of initial introduction, if known.
impacts (to the natural environment, humans, and the economy)
- Not all impacts have necessarily been observed in Nova Scotia. Some impacts may remain unknown.

This list does not include microscopic species (phytoplankton, zooplankton, and other microorganisms) that cannot be observed with the naked eye.

If you think you’ve discovered an aquatic invasive species, contact us to report it.

Image long description

Map showing the province of Nova Scotia and its surrounding coastal waters. On land, the borders of the counties of Nova Scotia are drawn on the map. From southwest to northeast, these are:

Shelburne
Yarmouth
Digby
Queens
Annapolis
Lunenburg
Kings
Halifax
Hants
Colchester
Cumberland
Guysborough
Pictou
Antigonish
Richmond
Inverness
Cape Breton
Victoria

The coastal waters of Nova Scotia are divided into the following subregions:

Bay of Fundy
Southwest
Eastern Shore
Cape Breton
Northumberland Strait

Aquatic invasive species in Nova Scotia

Species Name	Species Type	Habitat Type(s)	Known Locations in Nova Scotia	Pathways of Introduction and Spread	Impacts
Carolina fanwort (Cabomba caroliniana)	Plant	Freshwater	Frog Pond, Halifax	Escape: Pet* Stowaway: Biofouling; Fishing equipment	Quickly dominates invaded waterbodies Outcompetes native aquatic plants Reduces biodiversity by altering physical and chemical habitat for other species Overgrowth also inhibits recreational activities
Chain Pickerel (Esox niger)	Fish	Freshwater	Most watersheds throughout Nova Scotia except the northeast of the province (Guysborough, Antigonish, Cumberland counties) and most of Cape Breton	Release: Fishery in the wild	Competes with and eats native fish and other species, resulting in loss of biodiversity
Chinese Mystery Snail (Cipangopaludina chinensis)	Bivalve shellfish	Freshwater	Occurrences concentrated in Halifax Regional Municipality, but scattered occurrences have been noted throughout the rest of the province	Escape: Pet* Stowaway: Biofouling	Reaches high population densities, competing with native species for food and space Eats native algae, reducing their diversity Adults filter feed at high rates, altering water quality and nutrient cycling
Flowering Rush (Butomus umbellatus)	Plant	Freshwater	Scattered occurrences throughout Nova Scotia	Escape: Ornamental* Stowaway: Ballast water	Outcompetes native plants for space and resources, reducing biodiversity Dense stands can reduce water quality by lowering oxygen content and reducing flow Overgrowth also inhibits recreational activities
Goldfish (Carassius auratus)	Fish	Freshwater	Distribution unclear, but have been observed in freshwater lakes throughout the province, including in the Halifax Regional Municipality, the Annapolis Valley, and Cape Breton	Escape: Pet	Competes with native fish and other species for food and space Eats native species Increases suspended sediment through feeding activity, reducing habitat quality for native species Can spread diseases to native fishes
Koi (Cyprinus rubrofuscus)	Fish	Freshwater	Distribution unclear, but scattered reports from throughout Nova Scotia (e.g. in Halifax Regional Municipality)	Escape: Pet	Competes with native fish for food and resources Eats native plants and animals, reducing their abundance Increases suspended sediment in the water through feeding activity, reducing water quality and leading to algal blooms Can spread diseases to native fishes
Marbled Crayfish (Procambarus virginalis)	Crayfish	Freshwater	Yarmouth County	Contaminant: Contaminant of animals* Escape: Pet	Competes with native fishes for food and resources Eats native plants and animals Burrows damage infrastructure and interfere with agricultural operations
Red Swamp Crayfish (Procambarus clarkii)	Crayfish	Freshwater	Three Mile Lake, Halifax Regional Municipality	Release: Other release Escape: Live bait; Live food; Pet	Burrows destabilize shorelines and lead to infrastructure and property damage Modifies habitat by reducing density of aquatic plants and causing algal blooms Competes with native fish species for food and resources Eats native plants and animals Can introduce diseases, some of which can spread to humans
Smallmouth Bass (Micropterus dolomieu)	Fish	Freshwater	Many watersheds throughout southern and central Nova Scotia, with the exception of the northeast mainland and parts of Cape Breton	Release: Fishery in the wild* Escape: Live bait	Competes with native fishes for food and space Eats small native fishes and invertebrates, reducing biodiversity and abundance of native species
Spinycheek Crayfish (Faxonius limosus)	Crayfish	Freshwater	Freshwater Lake (Cape Breton)	Escape: Live bait*; Live food; Pet Contaminant: Contaminant of animals Stowaway: Fishing equipment	Competes with native fish species for food and resources and eats their eggs Burrows on shoreline, which can cause bank instability and damage to infrastructure Feeding and burrowing activity alters habitats by increasing sediment in water column and altering river and lake beds
Yellow Floating Heart (Nymphoides peltata)	Plant	Freshwater	Scattered occurrences in ponds around the province, most notably in Little Albro Lake, Dartmouth	Escape: Horticulture; Ornamental*	Dominates invaded waterbodies, outcompeting native plant species for space and nutrients Lowers water quality for native fishes and other animals Inhibits boating and recreational activities
Common Reed (Phragmites ssp. australis australis)	Plant	Freshwater Terrestrial	Throughout Nova Scotia	Contaminant: Seed contaminant Stowaway: Ballast water	Competes with native wetland plants for space and nutrients, reducing diversity
Narrow-Leaved Cattail (Typha angustifolia)	Plant	Freshwater Terrestrial	Throughout Nova Scotia	Stowaway: Watercraft excluding ballast water or hull fouling	Competes with native wetland plants for space and nutrients, reducing diversity
Purple Loosestrife (Lythrum salicaria)	Plant	Freshwater Terrestrial	Throughout Nova Scotia	Release: Other release Escape: Ornamental*; Watercraft excluding ballast water or hull fouling	Creates dense stands alter water flow Competes with native plant species for space and nutrients Impedes boating and recreational activities
Reed Canary Grass (Phalaris arundinacea)	Plant	Freshwater-Terrestrial	Throughout Nova Scotia	Release: Other release; Stabilization and barriers	Competes with native wetland plants for space and nutrients, reducing diversity Blocks watercourses by growing in dense stands
Yellow Iris (Iris pseudacorus)	Plant	Freshwater-Terrestrial	Occurrences concentrated in Halifax Regional Municipality, but scattered occurrences have been noted throughout the rest of the province.	Escape: Ornamental	Forms dense stands that alter water flow Compete with native plant species for space and nutrients Dries out wetlands by accumulating soil
Antithamnion sparsum	Seaweed	Marine	Eastern Shore; Southwest	Stowaway: Biofouling	May contribute to decline of kelp bed habitats by occupying space and increasing sedimentation
Asian Shore Crab (Hemigrapsus sanguineus)	Crab	Marine	Bay of Fundy, Southwest	Stowaway: Ballast water*; Biofouling	Competes with native crabs and the invasive European green crab for food and space Predates on native bivalve shellfish species (such as mussels) and potentially juvenile lobsters
Baltic Prawn (Palaemon adspersus)	Shrimp	Marine	Cape Breton; Eastern Shore; Southwest	Stowaway: Ballast water	May compete with native shrimp species for food and resources
Bay Scallop (Argopecten irradians)	Bivalve shellfish	Marine	Cape Breton	Escape: Aquaculture	None reported
Bladder Weed (Colpomenia peregrina)	Seaweed	Marine	Cape Breton; Eastern Shore; Southwest	Contaminant: Contaminant of animals* Stowaway: Ballast water; Biofouling; Machinery and equipment	Can attach to native seaweeds and may negatively affect their growth and survival Can attach to and displace farmed oysters
Bonnemaison's Hook Weed (Bonnemaisonia hamifera)	Seaweed	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Stowaway: Biofouling	May contribute to decline of kelp bed habitat by occupying space and increasing sedimentation Produces defensive chemicals that allow it to compete with native seaweed species for space
Chameleon Shrimp (Praunus flexuosus)	Shrimp	Marine	Bay of Fundy; Southwest	Stowaway: Ballast water	None reported
Clawed Fork Weed (Furcellaria lumbricalis)	Seaweed	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Stowaway: Biofouling; Watercraft excluding ballast water or hull fouling	Competes with native seaweed species of commercial importance, like Irish moss
Clubbed Tunicate (Styela clava)	Tunicate	Marine	Bay of Fundy; Cape Breton; Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling*; Fishing equipment; Machinery and equipment	Competes with native fouling species for food and space Fouls aquaculture stock and equipment, reducing harvests and increasing operating costs
Coffin Box Bryozoan (Membranipora membranacea)	Bryozoan	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Stowaway: Ballast water*; Biofouling	Lives primarily on kelp, forming colonies that weaken the kelp tissue and make the kelp more vulnerable to damage during periods of strong waves Has contributed to substantial losses of kelp habitat in Nova Scotia
Common Periwinkle (Littorina littorea)	Snail	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Escape: Live food Contaminant: Contaminant of animals Stowaway: Machinery and equipment; Packing material; Watercraft excluding ballast water or hull fouling	Competes with native molluscs for food and space Eats native seaweeds and shore grasses, altering habitats Provides food source for invasive Asian shore crabs and European green crabs Can introduce non-native parasites that can infect native species
Common Ragworm (Hediste diversicolor)	Worm	Marine	Bay of Fundy; Cape Breton; Northumberland Strait	Stowaway: Watercraft excluding ballast water or hull fouling	Constructs burrows in soft sediments, altering nutrient cycling and contributing to coastal erosion
Compound Sea Squirt (Diplosoma listerianum)	Tunicate	Marine	Bay of Fundy; Southwest; Cape Breton	Contaminant: Contaminant of animals Stowaway: Biofouling*; Machinery and equipment	Competes with native species, such as bivalve shellfish, for food and space, negatively impacting native species and ecosystems Disrupts aquaculture operations by competing with cultured species and fouling equipment
Convoluta convoluta	Worm	Marine	Only confirmed occurrence is in Halifax (Southwest), but likely more widespread	Stowaway: Ballast water*; Biofouling	May eat juvenile mussels, but impact is likely to be minimal
Dumont's Tubular Weed (Dumontia contorta)	Seaweed	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Stowaway: Biofouling	None reported
European Flat Oyster (Ostrea edulis)	Bivalve shellfish	Marine	Southwest	Escape: Aquaculture	None reported
European Green Crab (Carcinus maenas)	Crab	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Escape: Live bait; Live food Contaminant: Contaminant of animals Stowaway: Ballast water; Biofouling; Fishing equipment; Machinery and equipment; Watercraft excluding ballast water or hull fouling	Competes with native crabs and other species for food and space Significant predator of shellfish, disrupting aquaculture operations Destroys eelgrass beds, which are habitats for juvenile fish and other native species
European Mud Scud (Corophium volutator)	Amphipod	Marine	Bay of Fundy	Stowaway: Ballast water	Alters soft sediment habitat and nutrient cycling by constructing burrows Alters native food webs as a prey item for shore birds, fishes, and other animals
European Sea Squirt (Ascidiella aspersa)	Tunicate	Marine	Bay of Fundy; Cape Breton; Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling*; Machinery and equipment	Disrupts aquaculture operations through fouling and competition with stock species Competes with native species for food and space
Golden Star Tunicate (Botryllus schlosseri)	Tunicate	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling*; Machinery and equipment	Disrupts aquaculture operations through fouling and competition with stock species Competes with native species for food space Can harm eelgrass by growing on it
Gribble (Limnoria lignorum)	Isopod	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Stowaway: Biofouling*; Packing material	Causes damage to wooden structures in the water, such as docks
Japanese Skeleton Shrimp (Caprella mutica)	Shrimp	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Contaminant: Contaminant of animals Stowaway: Ballast water*; Biofouling; Machinery and equipment	Reaches high densities on artificial structures, interfering with aquaculture operations May compete with and displace native species living on hard surfaces (such as mussels)
Japanese Wireweed (Sargassum muticum)	Seaweed	Marine	Southwest	Stowaway: Biofouling	Competes with native seaweeds for space, altering habitat Can be a nuisance fouler of boats, fishing gear, and aquaculture equipment
Limy Tubeworm (Hydroides dianthus)	Worm	Marine	Southwest	Contaminant: Contaminant of animals Stowaway: Ballast water, Biofouling*; Machinery and equipment	Can cause heavy fouling and interfere with shellfish aquaculture operations
Mouse Ear Snail (Myosotella myosotis)	Snail	Marine	Bay of Fundy; Southwest	Contaminant: Contaminant of animals Stowaway: Machinery and equipment; Packing material; Watercraft excluding ballast water or hull fouling	None reported
Naval Shipworm (Teredo navalis)	Bivalve shellfish	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Stowaway: Biofouling	Causes damage to wooden structures in the water, such as docks
Orange-Striped Green Anemone (Diadumene lineata)	Anemone	Marine	Bay of Fundy; Southwest	Contaminant: Contaminant of animals; Machinery and equipment Stowaway: Ballast water; Biofouling	None reported
Orkney Weed (Lomentaria orcadensis)	Seaweed	Marine	Southwest	Stowaway: Biofouling	None reported
Oyster Thief (Codium fragile ssp. fragile)	Seaweed	Marine	Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Contaminant: Contaminant of animals Stowaway: Ballast water; Biofouling*; Fishing equipment; Machinery and equipment	Occupies space formerly occupied by native seaweeds (such as kelp) after disturbance events, preventing their recovery Alters habitat and composition of biological communities In Nova Scotia, effects appear to be temporary as stands of oyster thief can be removed by heavy wave action during storms, allowing native kelps to recover
Pancake Batter Tunicate (Didemnum vexillum)	Tunicate	Marine	Bay of Fundy; Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling*; Fishing equipment; Machinery and equipment	Forms extensive colonies that outcompete other benthic organisms for food and space Often overgrows and smothers other organisms on the seafloor, negatively affecting seafloor diversity and ecosystem functioning Can negatively affect wild stocks of commercially important species (such as scallops) Can interfere with aquaculture operations by fouling stock species and gear
Ribbed Bryozoan (Juxtacribrilina mutabilis)	Bryozoan	Marine	Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling*	Species lives mainly on eelgrass and could negatively impact it (by blocking light needed for photosynthesis, for example), particularly when present in high abundances
Siphoned Japan Weed (Dasysiphonia japonica)	Seaweed	Marine	Cape Breton; Eastern Shore; Southwest	Stowaway: Ballast water; Biofouling	Competes with and replaces native seaweeds for space, reducing biodiversity and altering habitat for native species Alters nutrient cycling Can form blooms of decaying algae that cause death of fishes and bivalve shellfish
Toothed Rockweed (Fucus serratus)	Seaweed	Marine	Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Stowaway: Biofouling; Fishing equipment; Watercraft excluding ballast water or hull fouling	Competes with native seaweeds for space, reducing biodiversity and altering habitat for native species
Tufty-Buff Bryozoan (Tricellaria inopinata)	Bryozoan	Marine	Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling*	Competes with native bryozoans and other species for space Can be a nuisance fouler of boats, aquaculture stock, and aquaculture gear
Twisted Sea Tubes (Melanosiphon intestinalis)	Seaweed	Marine	Bay of Fundy; Southwest	Stowaway: Ballast water; Biofouling	None reported
Vase Tunicate (Ciona intestinalis)	Tunicate	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling; Fishing equipment; Machinery and equipment	Competes with native species (such as bivalve shellfish) for food and space Disrupts aquaculture operations by competing with cultured species for space and fouling equipment Nuisance fouler of boats Alters nutrient cycling through intensive filter feeding
Violet Tunicate (Botrylloides violaceus)	Tunicate	Marine	Bay of Fundy; Cape Breton; Eastern Shore; Northumberland Strait; Southwest	Contaminant: Contaminant of animals Stowaway: Biofouling*; Machinery and equipment	Disrupts aquaculture operations through fouling and competition with stock species Competes with native species for food space Can harm eelgrass by growing on it
Yellow Sun Sponge (Halichondria bowerbanki)	Sponge	Marine	Bay of Fundy; Eastern Shore; Southwest	Stowaway: Contaminant of animals Stowaway: Biofouling*; Machinery and equipment	None reported
Beach-Flea (Orchestia gammarellus)	Amphipod	Marine-Terrestrial	Bay of Fundy; Cape Breton; Southwest	Stowaway: Fishing equipment; Packing material; Watercraft excluding ballast water or hull fouling	None reported
Common Sea Slater (Ligia oceanica)	Isopod	Marine-Terrestrial	Bay of Fundy; Southwest	Stowaway: Packing material; Watercraft excluding ballast water or hull fouling	None reported

Note: Where multiple pathways are listed, an asterisk (*) indicates likely mode of initial introduction, if known.

Pathways of introduction and spread

There are many ways for aquatic invasive species to arrive or spread as a result of human activities. Pathways for the aquatic invasive species that have been observed in Nova Scotia are described here.

Release

The transportation and intentional release of a species, with minimum human assistance after release. For example, the release of a sport fish for future angling.
This pathway can be further broken down into:
- Stabilization and barriers (plants introduced to stabilize soil and control erosion)
- Fishery in the wild (species introduced to establish wild populations for future angling)
- Other release (species introduced to establish wild populations for another reason)

Escape

The escape of a species from a confined or controlled environment. For example, dumping unwanted pets into a waterbody.
This pathway can be further broken down into:
- Aquaculture (aquaculture animals or plants establishing wild populations)
- Pet (unwanted or escaped aquarium animals)
- Horticulture (aquatic plants grown for commercial sale)
- Ornamental (aquatic plants for ornamental purposes, such as for use in ponds)
- Live food (species transported to be sold as food)
- Live bait (species used as live bait for fishing purposes)

Contaminant

The introduction of a species through the movement of other species or organic materials. For example, the movement of shellfish that are contaminated with invasive tunicates for aquaculture.
This pathway can be further broken down into:
- Contaminant of animals (species introduced because they are attached to or associated with transported animals, such as aquaculture animals)
- Seed contaminant (plant seed accidentally mixed with other seed and transported)

Stowaway

The introduction of species as a stowaways or hitchhiker on human-made materials. For example, the overland movement of an aquatic plant caught on a boat propeller. Contaminant: The introduction of a species through the movement of other species or organic materials. For example, the movement of shellfish that are contaminated with invasive tunicates for aquaculture uses.
This pathway can be further broken down into:
- Fishing equipment (species introduced because they are attached to or on fishing equipment, such as nets and clothing)
- Watercraft excluding ballast water or hull fouling for vessels sized >24m (species transported on non-wetted areas of large vessels)
- Machinery and equipment (species introduced because they are attached to industrial machinery or equipment, such as aquaculture equipment)
- Packing material (species accidentally included and transported in packing material, such as seaweed or straw)
- Ballast water (species introduced because they are carried in ballast water, which is used to control the buoyancy and stability of ships)
- Biofouling (species introduced because they are attached to the outside surfaces of ships and boats)

In addition to human-mediated pathways, aquatic invasive species also have some capacity for natural spread. For example, invasive species can spread through swimming or as larvae or fragments floating in the water.

Learn more about pathways of introduction and spread.

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