Wednesday, June 15, 2005

Musseled Out

Gulliver's Travels Revisited







Hagenius brevistylus larva with attached Zebra mussels, Photo by P. Myers.



Remember how the Lilliputians tied down Gulliver? They were small, but many. Zebra Mussels, are small, but they have tied down many a structure in the Great lakes due to their enormous numbers of individuals that accumulate. This latest blog entry was inspired by Phil Myers from the UM Museum of Zoology, currently teaching a summer course at the UM Biology Station at Douglas Lake. Phil has been the main force behind the Animal Diversity Web Project here at UM, and has been going wild with photographing insects with his Nikon digital SLR. At this point, he has far surpassed me in the number of insect photographs he has taken.

Phil was shooting odes around Douglas Lake, and saw that there were many Hagenius brevistylus (dragonhunter) trying to emerge and dying at the water's edge, when they could not break free from the coating of Zebra Mussels (Dreissena polymorpha) from the final larval instar. For a mobile hunter like the dragonhunter, the added weight of these mussels has to be a detriment. Of course, if they are covering the exoskeleton where the integument splits along the top of the thorax, the emerging adult will be trapped and die. We do not know how much of a detrimental factor the zebra mussels are to a population of lake-based dragonflies, and this could be a very interesting research project for a student at the Bio Station. This has to have a short-term negative impact on larger species that take longer to reach maturity (1-3 years for Hagenius).
In 2001, Margi Chrisincke wrote about Didymops transversa and Dromogomphus spinosus in Otter Lake that were encrusted by zebra mussels. About that time, I saw a Dromogomphus spinosus exuviae with a Zebra Mussel on the shore of Burt lake, just a few miles away from Douglas lake.


I encourage anyone else to share their observations on this phenomenon.


References:


CHRISCINSKE, M. 2001. Zebra mussels observed on dragonfly larvae in Otter lake. Williamsonia 5(4):9.

WEIHRAUCH, F. & J. BORCHERDING, 2002. The zebra mussel, Dreissena polymorpha (Pallas), as an epizoon on anisopteran larvae (Anisoptera: Gomphidae. Corduliidae, Libinellulidae)  Odonatologica. 31(1):85-94

1 comment:

Mark said...

Mark, Great picture! I was just up at UMBS and myself and Kevin Wehrly did a
little study on the mussels and how they might be affecting the dragonflies. More than 50% of the Hagenius had mussels on them and many of the Didymops did
as well. One effect we saw was that it may decrease their ability to right
themselves, they actually get stuck upside down when they have heavy loads of
mussels. Feel free to share any of this with the list- I wasn't sure how to
submit it. We're hoping to work up the data and put something out- it's pretty
disturbing as a whole.
Best,
Shannon McCauley