Washington Ascidian Homepage: Invasive Species

Identifications: Didemnum sp. Styela clava Ciona savignyi Botrylloides violaceus Botryllus schlosseri

REPORTING INVASIVE ASCIDIANS

There are 5 invasive ascidian species that should be reported if seen during dives. Please scroll down or click on the species links to read about their invasion history, to see photos and to learn how to identify them.
If you have, or think you might have, found an invasive ascidian(s) please note 1) location, 2) depth, 3) substrate (i.e. rock, wood), 4) how abundant it was (i.e. one, a few, a lot, everywhere), and if you can, get a clear picture of it. Then report it as follows:

For Didemnum sp., Styela clava and Ciona savignyi.
The state of Washington is very concerned about these 3 species. They have invaded other regions and have caused serious problems. So far in Washington they have been found in a few areas. It is important that we stop them from spreading.
  ***If you see any of these 3 species during your dives, please call 1-800-54-SOUND immediately.
  ****Also, if you see Didemnum, don't touch it! It can spread through fragments.

For Botrylloides violaceus and Botryllus schlosseri
I am interested in these 2 non-nuisance species,. They are common on docks and pilings and can overgow native species. The extent to which they have invaded more natural substrates is unknown.
****If you see either of these during your dives please email Erin Grey (egrey@uchicago.edu).

INVASIVE ASCIDIAN SPECIES

Didemnum sp. This colonial ascidian has already invaded other regions world-wide, where it has caused major problems. For instance, in the St. George's bank off the coast of Maine, Didemnum sp. has been found to cover 90 sq. mile of the ocean floor. Didemnum sp. has also invaded New Zealand, France, the Netherlands, California and British Columbia. It is unclear if all these invasions are of the same species... work is underway. In Washington Didemnum has been found at Edmonds Underwater Marine park, Gallagher Cove, Des Moines Marina and Taylor Shellfish (Quilcene and Totten Inlet). The invasion was effectively suppressed at Edmonds by putting plastic wrap over the colony and increasing the salinity. But for this method to work IT'S NECESSARY TO CATCH IT EARLY! Identification Color is usually light yellow/orange with darker grooves running through the colony If you look closely, there are little white dots in the colony- these are clusters of calcium-carbonate spicules (see close-up) When small, colonies tend to be thin and flat but when large starts to get "drippy". You CANNOT see two siphons or any regular arrangements of zooids- this may make it difficult to distinguish from a sponge. The best test is to feel it- but do so gently and don't break off any fragments!. Didemnum will be slimy while a sponge will feel like a sponge. And if it's Didemnum you can also see little pores close up upon touch. Tunicate identification card (pdf) for Didemnum sp. and Styela clava	close-up of Didemnum sp.- Note the small white dots and dark grooves Photo by Gretchen Lambert Large Didemnum colony looking "drippy" Photo by Frank Poole Didemnum colony growing in eelgrass Photo from Stachowicz's "Tunicates of the West Coast" at http://convoluta.ucdavis.edu/gallery/albums.php

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Styela clava Styela clava is native to Asia and has invaded many parts of the world, including western Europe, New Zealand, Australia, British Columbia, Prince Edward Island and New England. It can grow in very dense populations and causes serious damage to shellfish farms. In Washington large populations are currently established in Blaine and Pleasant Harbor (Brinnon). SCUBA divers employed by the Washington Department of Fish and Wildlife are attempting to eradicate these populations by removing large individuals by hand. Identification This is a stalked solitary species, with two conspicuous siphons that have dark vertical stripes (see photo). The tunic is often "warty". There is a similar looking native species, Styela montereyensis. This species tends to be more slender and smooth and lacks the dark vertical stipes on the siphons. Tunicate identification card (pdf) for Didemnum sp. and Styela clava	Styela clava hanging from a underneath a dock. Photo by George Arrow Styela clava close-up. Note the dark vertical stripes on the siphons and the bumps on the tunic. Hundreds of Styela clava on a mussel line. (Photo taken from http://www.skjell.com/aktiviteter/samlinger/harstad_02/10_pei-mussel.htm)

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Ciona savignyi Ciona savignyi is a translucent solitary ascidian from Asia. Like Styela clava, Ciona savignyi can be particularly problematic for the aquaculture industry when it takes off, as it can form dense aggregations that outcompete other sessile organisms, such as bivalves, for space and food. So far in Washington, Ciona savignyi has been found in Edmonds Underwater Marine park and various locations in southern Hood Canal. Identification This is a solitary ascidians whose tunic is almost completely clear. Yellow dots rim the siphons. Siphons are of unequal lengths Can form denses aggregations.	Ciona savignyi. Note the bright yellow stripes on the siphons. (Photo from www.calacademy.org/.../Ciona%20savignyi.htm) Ciona savignyi Photo by Gretchen and Charles Lambert

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Botrylloides violaceus This compound ascidian from Asia can be found in most temperate harbors and marinas through the world. It has probably been present in Washington for at least 25 years. It can be quite abundance and has been observed to overgrow other sessile organisms. Identification This is a compound ascidian and come in many bright colors (orange, red, yellow and purple are most common). The colonies are usually monochromatic, meaning just one color. Zooids are arranged in irregular oval systems with darkish lines or grooves between the groups of zooids.	Yellow colonies of Botrylloides violaceus. Photo by Erin Grey Three color morphs of Botrylloides violaceus (red, yellow & orange) Photo by Erin Grey Botrylloides violaceus (orange and pink colonies) dominates a settling plate. Photo by Erin Grey

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Botryllus schlosseri This species is thought to have originated in northern Europe and can now be found around the world. It has probably been in Washington for at least 25 years or more. Identification A compound tunicate that, like Botrylloides, also comes in many colors. It can be readily distinguished from Botrylloides violaceus because its zooids are arranged in a star-shaped pattern. Colonies are di-chromatic (two colors). Common morphs are bright orange/clear and dark blue/grey, with the bright orange morph being more common in Washington state.	Botryllus schlosseri on a settling plate. Note the star-shaped zooid arrangement and the di-chromatic coloration (bright orange/clear) compared to Botrylloides violaceus (dark orange). Photo by Erin Grey Blue/grey morph of Botryllus schlosseri dominates a settling plate. Dark orange colony on the left side is Botrylloides violaceus. Photo by Erin Grey

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