Notes

Notes

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Tunicate

Yes, it is a tunicate (also known as an ascidian or sea squirt) <http://en.wikipedia.org/wiki/Ascidian>, and I think the species is Aplidium californicum (see photo <http://seanet.stanford.edu/Urochordata/index.html#Aplidium_californicum> -note this photo doesn't match your specimen as well as other photos, but it is a nice web site). As the web site suggests, color is variable. The morphology matches this species description pretty well. It's a local species (that means it's not an invasive species), and there's not much known about it. I'm working on taking some photos under the microscope, and as soon as I have some, I'll send them to you.

Fouling of shellfish at farm sites by ascidians is well-known world-wide. I've looked a bit into control strategies, and they include
1. air exposure
2. freshwater exposure
3. salt-brine exposure
4. acetic acid exposure (similar to vinegar)
5. bleach exposure

I've looked into each of the treatments a bit. It's not clear which will be most effective in your situation. Sounds like you've already tried air exposure. How did that work? I could provide a brief explanation of some of the other methods. With any treatment, it will likely impact the oysters and take some effort. So there is a cost-benefit tradeoff. If the fouling is not impacting a large amount of your animals, then it may not be worth tackling it. The tunicate could easily spread, so it might be worth getting rid of the animals that are already fouled. But since this tunicate lives in the wild, it might be impossible to get rid of it completely.

Let me know if I can provide additional info.

Ginny L. Eckert, PhD
Associate Professor of Fisheries
Juneau Center, School of Fisheries and Ocean Sciences
University of Alaska Fairbanks
17101 Point Lena Loop Road
Juneau, AK 99801
voice: (907) 796-5450
fax: (907) 796-5446

We had 500 out of approximately 25,000 1" spat fouled with the Tunicate. They were allowed to set out for 24 hours ins a cool dry place. The Tunicate dried and then the spat was placed back in the water. After one month it appeared approximately 80% or more survived and the Tunicate was gone

Barnacles; In May of 2009 one raft of 100,000 2" oysters experienced a large barnacle hatch. The majority of the oysters were literally covered with 25-50 small barnacles. Several suggestions were made including dipping in hot water, bleach and fresh water. Treating 100,000 oysters would have been a monumental task. No measures were taken and it was discovered that 6 weeks later the oysters had appeared to have Grown Out of the barnacles and well over 95% had actually fallen off and died.

Naukati Bay Shellfish Nursery (907) 629-4147 boatahi@gmail.com

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