Aquatic invasive species

OYSTER THIEF

(Codium fragile spp. fragile)

Codium fragile, a green alga from Japan, first appeared in eastern Canada in 1989 in southern Nova Scotia. It appeared in the Gulf of St. Lawrence in 1996.

HABITAT

Codium lives underwater in subtidal areas down to 60 feet (18 meters) and can also be found in tide pools. Its holdfast allows it to attach to rocky bottoms, reefs, wharves and pilings, and even on other algae, molluscs or crustaceans. It is often found growing on eelgrass or drifting in bays.
Oyster thief  - DFO  S. Pereira
DFO S. Pereira

CHARACTERISTICS

Oyster thief - DFO  C. McKindsey
DFO C. McKindsey
  • Shaped like a small bush, soft and velvety as a sponge to the touch;
  • Colour: light to dark green;
  • Thick and spongy, Y-shaped cylindrical branches, 3 to 10 mm in diameter;
  • Size: up to 90 cm long;
  • Weight: up to 3 kg per plant;
  • When found on the beach, the branches may bleach white and resemble fat spaghetti.

SIMILAR SPECIES

Rockweed 
 MPO  R. Larocque
Rockweed
DFO R. Larocque

Codium can easily be distinguished from native seaweed species of the Gulf of St. Lawrence. Only the rockweed (Fucus distichus) has some similar characteristics such as its shrubby shape and its branching pattern. Unlike Codium, the rockweed's branches bear golden yellow vesicles filled with a gelatinous substance.

ECOLOGICAL AND ECONOMIC IMPACTS

  • Replaces native species;
  • Uproots eelgrass, a plant which provides shelter and reproductive and feeding habitat for fish, molluscs and crustaceans;
  • Can gradually overtake and replace kelp, which is a habitat for many species such as lobster and urchin;
  • When attached to shells, it prevents many molluscs from feeding, which makes them weaker and more vulnerable to predators;
  • May float away with oysters and other shells to which it is attached (explaining the name of "oyster thief");
  • Economic impacts on shellfish industries include loss of crop and fouling problems.
Eelgrass DFO S. Pereira
Eelgrass
DFO S. Pereira

WHAT YOU CAN DO