Most Unwanted:
Didemnum spp.
Habitat: Marine
Threat: Fisheries, protected species and marine ecosystem functioning
Status: Established
A colonial sea squirt from the Didemnum (pronounced die-DEM-num) group has recently been found fouling boats and marina structures in Ireland. This particular species of Didemnum is fast-growing and has the potential to out compete and smother a large number of native species. The threats posed are of concern to conservationists, aquaculture managers, and fisheries.
What is it?
Exact identification of this species is very difficult and can only be undertaken by a trained expert. However, in general native species are not found in large colonies and do not form the candlewax-like dripping structures, as seen in the photographs. Please see the Habitas website on Sponges of Britain and Ireland for more info on native species.
The invasive form can be describes as long, ropey or beard-like hanging from hard surfaces such as docks, aquaculture facilities, and ship hulls, or may be found as extensive mats covering rocky sea beds (pebbles, cobbles, boulders, and rock outcrops).
Impact
Alter marine habitats.
Interfere with fishing, aquaculture, and other coastal and offshore activities.
Increased fouling of manmade structures such as docks, moorings, and boat hulls.
Overgrow other organisms such seaweed, scallops, mussels, and oysters that depend on the seafloor for habitat.
May impact on underwater archaeological sites such as ship wrecks.
Produce noxious substances that deter most fish and other animals.
The colonies have been found at water depths ranging from intertidal to continental shelf depths of 65m (213 ft).
Where is it from?
Uncertain at present. The species is known from The Netherlands and France in Europe while worldwide the species is now recognised in Asia, Australasia-Pacific, Europe, and North America.
Where are they in Ireland?
Currently confirmed present in Carlingford Lough, Co. Louth, Malahide Marina, Co. Dublin and Galway Bay, Co. Galway.
How did it get here?
Uncertain at present. Likely vector is fouling of ocean going vessel and/or contamination of aquacultre produce.
How is it spreading in Ireland?
Once the species becomes established in an area, it can spread rapidly by both sexual reproduction and asexually by fragmentation of the colonies. Species is known to grow on mobile organisms such as crabs. Fouling on sea going vessels is a key vector in dispersal of this species. The species may also establish itself with movement of shellfish for the aquaculture industry.
What you can do
Do not interfere with colonial tunicates. These species can spread more rapidly when a section of the colony becomes detached and carried with currents to new areas. If you can do so safely, photograph the species.
Everyone is urged to thoroughly wash and dry all equipment that was near an infestation of this species. This is essential to avoid contamination of new areas. It is important to do this where the rinse will not return to the marine environment. New infestations may result if you do not undertake this.
Report all sightings.
