Thursday, October 19, 2017

Small Mussels with Big Effects: Invasive Quagga Mussels Eat Away at Great Lakes Food Web

Thursday, April 10, 2014

by Kathe Glassner-Shwayder, NOAA Great Lakes Environmental Research Laboratoryand Bonnie Myers, NOAA Research Office of Communications

Since hitching unsolicited rides in boat ballast water in the late 1980s, invasive quagga mussels (Dreissena rostriformis bugensis), which are native to Ukraine, have caused massive changes to the ecology of the Great Lakes.  These invasive mussels have also taken a toll on the Great Lakes recreational and commercial fisheries, which are valued at $4-7 billion annually according to Michigan Sea Grant.

The quagga mussel had a sluggish start in its early expansion but is now present in large numbers far exceeding those of another invasive mussel in the Great Lakes, the zebra mussel, according to a publication by NOAA’s Great Lakes Environmental Research Laboratory (GLERL).

The filter-feeding quagga mussel has a high filtering rate for its size, and coupled with its high abundance, has a significant impact in invaded ecosystems, like the Great Lakes.  The mussel uses hair-like cilia on its gills to pull water into its shell through a siphon-like structure.  Materials collected are then sorted for ingestion inside the shell or for rejection through the siphon.

Quagga Mussel’s Siphon Functions as Feeding Tube

Quagga Mussel’s Siphon Functions as Feeding Tube

The mussel uses hair-like cilia on its gills to pull water containing food particles into its shell cavity through its siphon. Credit: NOAA
By filtering phytoplankton and other materials from lake water, quagga mussels alter both lake habitat and the food web.  For example, through their large appetites for phytoplankton, the quagga mussels rob the food web of an important food source for native and non-native fish.

Scientists have a limited understanding of the quagga mussel’s feeding habits, like the type and size of phytoplankton consumed in the quagga’s natural environment.  Thus, scientists from NOAA’s GLERL, the University of Michigan's Cooperative Institute for Limnology and Ecosystem Research, and South China Agricultural University recently conducted the first study of quagga mussel natural feeding habits in the Great Lakes to better understand the mussel’s effects on the food web.

NOAA Researcher Collects Mussels

NOAA Researcher Collects Mussels

Using a wire mesh dredge, the bottom of Lake Michigan is sampled for dreissenid mussels Credit: NOAA
The researchers used microscopic techniques, rarely used in these types of studies, to identify, count, and measure the quagga mussel’s consumption of naturally occurring phytoplankton species found in Saginaw Bay, Michigan.  Previous studies evaluating quagga mussel feeding habits used laboratory-cultured algae in place of natural phytoplankton communities, making this study unique and useful for predicting the mussel’s effects on natural ecosystems.

Surprisingly, the study found quagga mussels preferred to feed on specific phytoplankton species, rather than a particular size of phytoplankton, like how one might choose a banana over an apple.  This unanticipated finding of quagga mussel’s preference to certain phytoplankton species, like flagellates or diatoms, over phytoplankton size could have important implications on the food web. 

“This study is extremely significant given the unexpected results that showed quagga mussels are highly selective filter feeders and that the changes we have been seeing in the Great Lakes food web are likely driven by selective feeding of dreissenid [quagga and zebra] mussels,” said GLERL lead scientist, Dr. Henry Vanderploeg.

Flagellate Phytoplankton, Rhodomonas

Flagellate Phytoplankton, Rhodomonas

Quagga mussels prefer to ingest this species of phytoplankton, since it lacks a protective shell. Credit: NOAA
Quaggas preferred eating the highly nutritious, naked flagellate, Rhodomonas, over the silica-shell encased diatom, Cyclotella.  The naked flagellate phytoplankton, having no protective walls, is likely easier to digest compared to the hard-shelled diatom, which may pass through unprocessed or rejected before ingestion.  On the other hand, large diatoms of different species are readily ingested.

Diatom Phytoplankton, Cyclotella

Diatom Phytoplankton, Cyclotella

Quagga mussels may reject this small diatom because it is encased with silica, making ingestion and digestion difficult. Credit: NOAA
In fact, small diatoms are usually considered good food for most mussels, but not for the quagga mussel, which rejects small diatoms during the feeding process. The quagga mussel also rejects the cyanobacterium, Microcystis, through forceful expulsion in this quagga feeding video. Unfortunately for the Great Lakes, cyanobacterial blooms, commonly known as blue-green algae, can cause death of nearby fish and foul up nearby coastlines.

“The importance of quagga mussels in driving change in phytoplankton communities [was] an important lesson learned from this research,” noted Huijuan Tang, the lead author, from the College of Animal Science in the South China Agricultural University, on the paper, “Quagga mussel selective feeding of phytoplankton in Saginaw Bay,” which was published in the Journal of Great Lakes Research.

 “Since quagga mussels have many similarities with zebra mussels and marine mussels, [these] results may help anticipate changes caused by mussels in other invaded aquatic systems and in North America [e.g., Lake Granby and Lake Mead in Colorado],” said Tang.




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