Small but deadly: Meet Haida Gwaii’s Aquatic Invaders

Japanese Skeleton Shrimp (Caprella mutica) are amphipod crustaceans from eastern Asia. The species is now found in Haida Gwaii waters, including the Masset dock, Skidegate Inlet, and Cumshewa Inlet. This species are often found in large numbers on infrastructure such as buoys and shellfish aquaculture equipment. There is some evidence to suggest that they compete with mussels for food and space. Photo credit: Department of Fisheries and Oceans

Molly Clarkson —

Haida Gwaii has its fair share of invasive species, some of them are all around nuisances, such as the racoons and rats that lay waste to seabird colonies, while others like the Sitka black-tailed deer have had a mix of impacts – some negative (reduced vegetation cover and plant species richness) and some positive (charred venison backstrap with horseradish cream sauce, anyone?).

A species is considered “invasive” if it meets two criteria. First, it must be an alien species, which is any species that is not native to the area.  Second, it must have negative ecological, social, and/or economic effects in the area that it has invaded.

There are over 30 alien marine species in the waters of Haida Gwaii, but most do not seem to have a significant negative impact.  A few of these alien species may be detrimental to Haida Gwaii, but we do not know enough to understand their impacts.  These potentially harmful aliens include Japanese skeleton shrimp (Caprella mutica), Japanese ogonori seaweed (Gracilaria vermiculophylla), and Japanese wireweed (Sargassum muticum).  However, the aliens of most concern to us are two species of invasive tunicates that were recently introduced to Haida Gwaii and that are known to cause significant ecological and economic impacts.

While there are some native types of tunicates in Haida Gwaii, the extensive, gelatinous and brightly coloured organic mats created by the recently introduced Chain tunicate (Botrylloides violaceus) and the Star tunicate (Botryllus sclosseri) pose significant risks to the marine environment. Both species spread quickly, smothering native seaweeds, barnacles, shellfish and anything else in their path. These species of tunicates are also known to disrupt shellfish aquaculture operations by growing over cages and other infrastructure, creating a significant economic cost.

These two types of tunicates have been detected in Masset and Skidegate inlets and around Langara Island (Egeria Bay) and the Bischof Islands in Gwaii Haanas. In a recent survey of the Masset and Queen Charlotte docks, the Haida Fisheries and the Haida Oceans Technical Team found significant growth of the Chain and Star tunicates just a foot below the low tide line. Tunicates have also been found growing on the hulls of boats moored at these locations.

As part of implementation of the Haida Gwaii Marine Plan, the Council of the Haida Nation and the Province of BC will be working with the Fisheries and Oceans Canada, Gwaii Haanas, and other agencies to develop a strategy to prevent the introduction of new aquatic invasive species and stop the spread of species that are already here. This will include an expanded monitoring program, and a survey of vessel traffic.

There are a number of other invasive aquatic species that pose a risk to Haida Gwaii but which have not yet been recorded here. Understanding the way these species spread is a good first step towards developing methods to prevent their introduction, though in some instances, like the European green crab (Carcinus maenas), the spread is caused by natural phenomena such as larval dispersal and is therefore not controllable.

Understanding how aquatic invaders that are already present in Haida Gwaii spread from place to place is also important. The invasive tunicates are particularly abundant at dock sites because they are spread on the hulls of boats. They can also be spread by gear from shellfish aquaculture and fisheries.


The Chain tunicate is impossible to eradicate once it becomes well established like it is in Masset Harbour and Skidegate Inlet.  However, if we are fast enough in detecting it in a new area, we may be able to eradicate it before it becomes established.  Early detection is key, so keep your eyes peeled for any invasive tunicates.

Please contact Stuart Crawford ( or 250-626-3302) if you come across any of these listed invaders in a new area of Haida Gwaii.


Because it is impossible to eradicate the Chain tunicate once it has become established, it is very important to prevent its spread. It does not spread far naturally but is instead introduced to new areas on the hulls of boats and on other marine equipment, particularly during the warmer months of the year.

The only effective way to kill the Chain Tunicate is to let it dry out. To play your part in halting the tunicate invasion, consider taking these precautions this upcoming season:

  • DO NOT scrape the organism off in the water. Each small piece can grow into a new colony.
  • Dry off floats and other gear (including fishing gear) for at least 48 hours before heading into a new area;
  • Clean your boat on land.  Let it dry off for 48 hours, and then clean it in an area where the run-off will not run into the ocean;

If you are concerned about your boat spreading invasive tunicates, please contact Stuart Crawford ( or 250-626-3302) for suggestions on best practices.


1 Comment

  1. Early detection for aquatic invasive species is important for management, Not sure if EDDMapS is used much in BC, but has been useful in tracking aquatic invasive animals and plants (mystery snails, water soldier, etc.)

    Thanks for the great article!

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