|MadSci Network: Environment & Ecology|
The alga you're asking about is a type of cyanobacterium (formerly known as "blue-green algae"),belonging to the genus Microcystis (the exact species are, as yet, uncertain), that is known to produce toxic blooms.
I did a quick search at Yahoo, and found 18 hits under "Microcystis" and "Zebra mussel". You can check them out here.
The most clear are right at the top, and are a couple of abstracts, one from a presentation at a scientific conference, and one from a paper:
Zebra mussels are filter feeders, and any selection of food particles is done after the particle has been captured. It works like this: the mussel sucks in water through one end of its shell, and filters particles out of that water with its gills. The gills, which are modified for feeding, are covered in small cilia, that can move the captured particles. At the same time, the particles are "tasted" by the gills. Particles that are palatable are passed along the gills to the mouth, while unpalatable particles are passed along the outside of the gills and to the exhalent siphon, which is where the water that has been filtered exits the shell. The unpalatable particles often stick together (aided by mucus from the mussels' gill) and form a string of material. Because this material looks a lot like the mussels' feces, the stuck-together unpalatable particles are called pseudofeces.
It looks to me that in the presence of Microcystis, zebra mussels will either not ingest them and expel them as pseudofeces (where the Microcystis can then presumably reinnoculate the water column); or reduce their feeding rate or stop feeding alltogether, thus allowing the Microcystis to bloom. As well, it seems that some strains of Microcystis are more toxic than others (the toxin is called "microcystin"), and zebra mussels will happily eat less toxic strains.
Hope that helps!
Rob Campbell, MAD Scientist
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