Invasive Tunicate Species Management Program

The Washington Department of Fish & Wildlife (WDFW) is charged by the state legislature to prevent the introduction or spread of prohibited and unlisted aquatic animal and plant species. This effort supports WDFW’s goal to achieve healthy, diverse and sustainable fish and wildlife populations and their supporting habitats; and the Puget Sound Partnership’s Action Agenda Priority A.5 in protecting ecosystem functions by preventing and rapidly responding to the introduction of invasive species.

The WDFW Aquatic Invasive Species (AIS) Unit is tasked with implementation of an Invasive Tunicate Species Management Program, which was developed in consultation with the stakeholder Tunicate Response Advisory Committee (TRAC).

The program is built on an adaptive management structure and uses a collaborative approach to addressing invasive species. This plan is one of many WDFW management plans developed, or in development, by the AIS Unit as part of its overall strategic plan. The basis of all AIS management programs are six unit goals including:

1) Prevent the introduction of new AIS;
2) Control, contain, or eradicate established AIS populations;
3) Predict and detect new or recurring AIS;
4) Coordinate / collaborate in state, regional, national, and international AIS processes;
5) Promote public education and volunteer opportunities; and
6) Promote biodiversity and restoration.


Tunicates are innocuous-looking organisms that are particularly prolific spawners, in some cases, reproducing once every 24 hours when the water temperatures warm to the right conditions. They can out-compete native organisms for food and space. They attach to boat hulls, docks and marina structures, and also to shell stock and shellfish-growing equipment. Tunicates are also called ascidians or sea squirts based on their taxonomic lineage.

  • Domain: Eukaryota Whittaker & Margulis,1978
  • Kingdom: Animalia Linnaeus, 1758
  • Subkingdom: Bilateria (Hatschek, 1888) Cavalier-Smith, 1983
  • Branch: Deiterostomia Grobben, 1908 - Deuterostomes
  • Infrakingdom: Chordonia (Haeckel, 1874) Cavalier-Smith, 1998
  • Phylum: Chordata Bateson, 1885 - Chordates
  • Subphylum: Tunicata Lamarck, 1816
  • Class: Ascidiacea Blainville, 1824 - Sea Squirts

There are seven non-native tunicate species currently reported as established to some degree in Washington state waters. Three of these are of primary invasive concern to WDFW resource managers (green-shaded rows) to stakeholders and are the focus of the department’s management program. The remaining four are of secondary invasive concern as they have not demonstrated a substantive invasive threat, but are being monitored within the context of the management program.

Click on the scientific name for more detailed information.
Scientific Name

Common Name

Invasive Level

Styela clava

Club tunicate


Ciona savignyi

Transparent tunicate


Didemnum vexillum

Colonial tunicate


Botrylloides violaceus

Chain tunicate


Botryllus schlosseri

Golden star tunicate


Molgula manhattensis

Sea grape tunicate


Ciona intestinalis

Vase tunicate


Potential Risks
Tunicates are evolutionarily advanced invertebrate marine animal organisms. The species listed above are documented prolific spawners capable of rapid territorial expansions when introduced to regions outside their native range. Once established, these tunicates can displace most native organisms by out-competing them for food and space, and potentially by consuming the spawn or larvae of other marine species. The presence of non-native tunicates can lead to profound disruptions of naturally functioning ecosystems by altering species interactions, nutrient cycling, and energy flow (Carlton 2001). Disruptions to the natural biological and physical processes of marine communities often leads to decreased biological diversity on local scales and increased ecosystem homogenization over much larger geographic scales (Ruesink 1998). Marine resource management strategies in Washington rely primarily on natural production to maintain and restore populations. Natural production of native species is heavily dependent on the biodiversity afforded through the structure, function, and integrity of undisturbed ecological systems.


Information and Reports