Last Day of the Season...for Mussels

Today was probably my last field day this year for sampling Western Pearlshell mussels (WPM) for signs of gravidity. Sad! The flow is low and the mussels are burrowing deeper into the substrate, making it harder to find them. At this time of year, when you pull a WPM out of the substrate, they sometimes squirt you and sometimes make noises. Maybe a bit more stressful with less flow and warmer temperatures? Or just a habit of theirs. I guess I wouldn't be quiet if I was pulled out of my habitat either .

Two new people in our office came out to help me. Rachel and Doug. They will mostly be working with the lamprey crew, formally known as the non-salmonid team, for the rest of the summer. Anyway, neither one of them had done any mussel work so they were excited and ready to go. Freshwater mussels already fascinate me so their enthusiasm made it even more fun.

There are few people who come out with me who actually will sample the mussels. You see, in order to check for gravidity we must open the mussel up about a centimeter to inspect their gills. That's where the mussel broods its eggs. So when I asked them if they wanted to sample they delightedly said Yes. I sampled the first couple of transects and showed them what to do and they pretty much took over after that.

The weather could not have been better and the company was excellent. What a great day. Thanks Rachel and Doug. I hope you enjoy your time at the CRFPO.



For more mussel blogs check out mussel mania I posted Feb 2010 and mussel mania II posted in May 2010.

Submitted by Donna Allard

Mussel Mania Part 3 - Glochidia

Glochidia size compared to a dime.

Well, last time I wrote about seeing seeing the mussels releasing their larvae (called a spat). You can read about it at Mussel Mania Part 2. Anyway, at the time, I gathered up a net and some containers and scooped up some of the conglutinate masses to verify that these masses actually contained glochidia. As soon as I got back into the office, I went to the lab where we have a microscope with a camera attachment, and sure enough, the masses were filled with glochidia. Most of them looked like spheres but some of them which were opened looked like little pacmen. The glochidia are only .05mm in length. Not hardly visible with the naked eye. If these glochidia (well, not the ones I collected) are lucky enough to find a suitable host and attach to the gills, they will actually grow to twice their length (about .4mm which still isn't that large) before falling off and beginning their life as free living mussels. That is, if all goes well.

Glochidia clusters, open glochidia

Mussel Mania Part 2

Western Pearlshell mussel releasing conglutinates.

OK, in February I wrote a bit about the reproductive cycle of freshwater mussels. Well, last week I witnessed part of the cycle. It was very exciting. Apparently Western pearlshell mussels release conglutinates, a mucousy white mass filled with glochidia (mussel larvae). The conglutinates break up in the water current and settle to the bottom of the stream, where they resemble little white worms. That's the easy part of the life cycle. Soon after being released, a suitable host fish needs to eat 'the worm'. After being ingested, the glochidia attach to the gills of the fish and begin their transformation into free living mussels. That is, if all goes well!

Wormlike mass of glochidia.

Mussel Mania - Part 1

I never really thought about freshwater mussels until a few years back. Now I think about them all the time. Especially since I will soon be conducting a small pilot project studying them in Merrill Creek. More on that later. They are fascinating creatures. Even though they are one of the most endangered groups of animals on Earth, very little is known about the life history and habitat needs of many species.
We do know that freshwater mussels are dependent upon fish. After mussel larvae, called glochidia, are released from the female into the water, they have a very short time to find a host fish. If they find one, they will clamp onto its fins or gills, form a cyst around itself, and remain there for days or even months. During this time, the fish may swim many miles, thus helping to disperse mussel populations. Anyway, the chances of glochidia finding a suitable host, (yes, some mussel species are dependent upon only certain species of fish), landing in a suitable habitat after detaching, and reaching adulthood can be as high as 1 in 100,000,000. All I can say is WOW. Stay tuned for more interesting facts about freshwater mussels. If this has piqued your interest, go to the Pacific Northwest Native Freshwater Mussel Workgroup. There you can read a few documents or download the 2nd edition of the Field Guide to the Freshwater Mussels of the Pacific Northwest. And if you are ever wandering around in a creek and find any mussels, I’ll bet they would love to know.