Aquatic Invasive Species

What is an invasive species?

An invasive species is an organism that has either extended their traditional range by natural means or have been unwittingly or intentionally brought to new areas.

Since 1997 there have been seven new invasive species that have impacted the aquaculture industry in PEI:

Green Crab

Close up of a green crab holding a live mussel shellfish. The crab is attempting to use its claws to open the mussel shellfish. On the left side of the picture are several vase tunicates (approx. 30 mm in length with a transparent outer covering).
Image caption: 
A green crab is attempting to eat a blue mussel. Several vase tunicates are also pictured on the left.
The Green Crab is a serious predator of shellfish such as clams and mussels. It is very destructive to eel grass beds, uprooting the eel grass and leaving holes along the shore. It is a very hardy animal, able to survive extended period out of the water. It can be found in most river systems on the eastern end of PEI but has not been found in significant quantities in other areas of the Island.

The Green Crab can be differentiated from the native rock crab by its dark mottles green colour and a row of distinctive yellow dots along the dorsal side of its shell. It is smaller than the rock crab and has distinctive points on the front edge of its shell. It is much more aggressive than the rock crab.

See a map of the areas currently populated with the green crab.

Oyster Thief

The oyster thief is a fast growing green seaplant that can reach lengths of 60 centimeters (2 feet). It has gained its name because when it attaches to oysters, the buoyancy of the plant can cause the oyster to float away.

Heavy growth of the oyster thief can also obscure oyster beds and increase the cost of harvesting.

It is able to spread quickly because as fragments of the plant break off, they are able to reattach and form a new plant. The plants also reproduce by releasing spores which can also travel some distance before they settle and form a new plant.

See a map of the areas currently populated with the oyster thief.

Clubbed Tunicate

Close up of gear, including a square wire cage and the attached rope sits on an asphalt surface. The gear has been completely covered by hundreds of clubbed tunicates. The tunicates are approximately 50 mm in length and look like a medieval club a
Image caption: 
Clubbed tunicates are shown heavily fouling gear used in the Mussel Monitoring Program. The tunicates have covered the wire cage and the rope attached to it.

The clubbed tunicate was first found in PEI in 1998 in the Brudenell River. It has a cylindrical body and can grow up to 15 centimeters (six inches) in length. It attaches to a substrate by means of a holdfast at the end of a thin stock which protrudes from the posterior end. It has a warty surface with mottled colour. The smaller clubbed tunicates appear as miniature versions of the large ones with a smoother surface.

It is typically found in dense clumps growing below the water level on substrates such as docks, buoys, hulls of boats, etc. They attach very firmly, making them very difficult to remove.

The clubbed tunicate can live for several days out of water. The spawning period for the clubbed tunicate in PEI water is from the middle of June to the middle of October. The adults can spawn and the offspring can potentially infest new substrates within a period of a few days.

The clubbed tunicate poses a serious challenge for the mussel aquaculture industry in PEI. Both growers and processors have been affected in some areas. The fouling caused by the tunicates is problematic as the cost of production is increasing for both growers and processors. Restrictions on the movement of shellfish from tunicate infested areas have been put in place.

See a map of the areas currently populated with the clubbed tunicate.

Vase Tunicate

An underwater picture showing hundreds of vase tunicates attached to a rope. The tunicates are a transparent orangish colour. They have a cylindrical body with two siphons that are used to filter the water for food.
Image caption: 
Hundreds of vase tunicates are shown attached to a rope in the Montague River, PEI.
The vase tunicate was first found in PEI in 2004. It has a soft cylindrical body with a smooth transparent surface and grow up to 15 centimeters in length (six inches). There is often a red area inside the tunicate which makes them easy to identify.

This tunicate attaches to hard substrates in subtidal areas. When present in large numbers it resembles a jelly-like mass.

The fouling caused by the tunicates is problematic as the cost of production is increasing for both growers and processors. Restrictions on the movement of shellfish from tunicate infested areas have been put in place.

See a map of the areas currently populated with the vase tunicate.

Golden Star Tunicate

A hand is holding a cluster of green eel grass that has been covered by the goldenstar tunicate. The tunicate grows as a colony and is a brownish colour.
Image caption: 
Colonies of the goldenstar tunicate growing over eel grass.
The golden star tunicate was first found in PEI waters in 2001 in St. Peters Bay. It covers the substrate on which it is growing like a mat. The size of the colony is only limited by the size of the substrate. Colonies typically are 1 to 3 centimeters in thickness but can range from a few millimeters up to 5 centimeters. These tunicates will grow on hard substrates in subtidal areas. It is common to find them growing on eel grass and other marine plants. As these plants break off, the potential for the tunicates to spread increases. It is typically dark in colour with a lighter star shaped pattern, but may also occur in a variety of other colors.

The golden star tunicate will attach to and grow on marine plants as well as hulls of boats and floating structures in the water column.

Small pieces of a colony can easily be transported within a body of water or to new bodies of water on pieces of floating marine plant material or inadvertently by water users.

See a map of the areas currently populated with the golden star tunicate.

Violet Tunicate

Green eel grass covered with an orange organism, the violet tunicate, is pulled from shallow water using oyster tongs. Oyster tongs resemble two rakes attached together by a hinge in the middle.
Image caption: 
Eel grass covered with the violet tunicate is collected using oyster tongs.
The violet tunicate was first found in PEI waters during the summer of 2002 in Savage Harbour. It is a colonial tunicate that covers the substrate on which it is growing like a mat. The size of the colonies are only limited by the size of the substrate on which it is growing. Colonies typically are 1 to 3 centimeters in thickness but can range from a few millimeters up to 5 centimeters. It has several different colour variations from tan to bright orange. It often has a ridge or track like pattern through the colony. The violet tunicate will attach to and grow on marine plants as well as hulls of boats and floating structures in the water column.

Small pieces of a colony can easily be transported within a body of water or to new bodies of water on pieces of floating marine plant material or inadvertently by water users.

See a map of the areas currently populated with the violet tunicate.

Oyster Drill

The oyster drill is emerging as a predator of oysters in PEI waters. It has been present since the early 1900's, but in recent years has become established in a growing number of oyster producing areas. The oyster drill is able to make a small hole in the oyster shell through which it is able to consume the oyster. The population can spawn from May to October, but each animal will only spawn once. The eggs are contained in egg casings, which are quite often found on hard objects such as rocks or oysters on the bottom.

See a map of the areas currently populated with the oyster drill.

Published date: 
February 8, 2016
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General Inquiries

Department of Agriculture and Fisheries
PO Box 1180
548 Main Street
Montague, PE   C0A 1R0
Phone: (902) 838-0910
Fax: (902) 838-0975

peiextension@gov.pe.ca