Saturday, April 23, 2016

(1) Alien Mussels Dominate Lake Bottoms, Scramble Ecology

--- first in a series ---

Hello, invasive zebra and quagga mussels. Goodbye: introduced salmon, invasive alewives, native Diporeia, diatoms and on and on.


Invasive quagga mussels have out competed their cousins, zebra mussels, at the bottom of Lake Huron and Lake Michigan. Quaggas tolerate colder, deeper water and thrive on mud bottoms. Zebras prefer to attach themselves to less abundant hard surfaces.

Both are efficient filter feeders and prolific breeders. Small quaggas can filter a quart of water daily. Billions of them cover the bottoms Lake Huron and Lake Michigan.

Diatoms are single cell plants, a form of algae, that make up part of the quagga’s diet. Diatoms envelop themselves in a hard shell of silica taken from the water.

The process is useful to mussel researchers as a marker of or proxy for total algal density, i.e. an extrapolation of the quantity of all algae in the water.

Diatom blooms occur in the spring. As the plants absorb silica and sink to the bottom, a reduction or drawdown of silica in the water is measurable. Less silica means more diatoms; more diatoms implies more algae in general.

In 2008, EPA researchers found that silica in the water was 80% lower than 30 years earlier, indicating a similar reduction in algae and coinciding with the proliferation of quaggas, which began in 2004 in Lake Michigan.

“By filtering out the algae, the mussels are robbing other organisms of the food they need to survive. Of particular concern is the plight of Diporeia, a tiny shrimplike creature that was one of the pillars supporting the base of the Great Lakes food web. Nearly every fish species in the Great Lakes relies on Diporeia at some point in its life cycle. But Diporeia populations have crashed in lakes Michigan and Huron, and the change is already impacting Great Lakes commercial fisheries and the sport-fishing enterprise.”

It’s worth noting, however, that in Lake Huron, where the salmon/alewife-heavy ecology crashed first, native species like lake trout have rebounded and invasive gobies have entered the picture.

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