Impact of Quagga Mussel Introduction on Particulate Organic Matter Drift, Ecosystem Level Impacts
Project ID: 3997
Principal Investigator: Mike Horn
Research Topic: Invasive Species
Priority Area Assignments: 2011 (Zebra and Quagga Mussels), 2012 (Zebra and Quagga Mussels)
Funded Fiscal Years: 2011 and 2012
Quagga mussels, since their appearance in the Colorado River system over the past several years, have quickly come to dominate much of the available habitat in reservoirs and many portions of the Colorado River itself. Once their populations reach high levels, they are known to be effective at altering food webs, as has been demonstrated in the Great Lakes, through their efficient filtering of particulate organic matter (POM) from the water column. This can lead to changes in the entire food chain, potentially impacting sport fisheries, native and endangered species, and water quality in reservoirs and downstream areas.
An effort is currently underway to determine changes occurring within Lake Havasu. This research will complement that ongoing study. POM supports the base of the food web in aquatic systems and is one of the many factors determining the makeup of aquatic communities in riverine ecosystems. Small size POM typically makes up the largest portion of the drift below reservoirs, and it is these smaller size classes that quagga mussels may be most efficient at filtering. Changes in specific POM size classes can have a large effect on drift feeding invertebrates and, thus, the food chain for many riverine systems. Such changes can significantly impact fish populations including sport fisheries and native fish communities (including endangered species) in the affected reach. Water quality can be impacted directly through selective filtering by quagga mussels, resulting in undesirable algal species such as blue-greens becoming dominant, and indirectly through changes in the aquatic food web where changes in nutrient dynamics can occur.
Understanding how mussels affect POM and water quality in the Lower Colorado River will provide valuable information when trying to predict impacts in other areas as the mussels spread as well as help identify issues that may be impacting ecosystem health in the lower river.
Need and Benefit
This study represents a unique opportunity to examine the impacts an invasive aquatic organism has, and is having, on the ecosystem. Few studies are around where there exist good data, pre-introduction of an invasive species. It was fortunate that such a large-scale study looking at organic matter drift, the food base for much of the riverine ecosystem, was conducted on the Lower Colorado River.
As has been seen in other areas where mussels have appeared, large changes in the structure and function of lakes and rivers have been observed, often to the detriment of commercial and sport fisheries, as well as the noted declines of many native species. Many Bureau of Reclamation (Reclamation) projects have significant investment in helping maintain or restore sport fisheries and/or native species whose survival has been impacted by ongoing operations. Much of this effort has been predicated based on the conditions present in the reservoirs and rivers.
If there are significant changes to these ecosystems, Reclamation may be forced to find new ways to limit impacts to the species of interest. Such a study should allow planners a better insight into what the future holds should this species appear in their systems. This study complements well several other studies also being funded through the Science and Technology Program. In particular, the proposal to look at water quality changes on Lake Mead would tie in well with this study due to the linkages between what is happening in the reservoir and downstream conditions.
Several of the other proposed studies, such as those by Nelson and Lieberman, also complement this study, and the results of those studies will be integrated into the final report for this study. Each of the other studies, while addressing quagga mussel introduction, takes a slightly different approach to looking at the environmental effects. Melding the results of all these studies at the end should produce a more complete picture of the overall impacts of quagga mussel introduction on Reclamation- controlled systems.
The following documents were not reviewed. Statements made in these documents are those of the authors. The findings have not been verified.
Impacts of Quagga Messels on POM (final, PDF,
By Mike Horn
Report completed on December 15, 2014
This information was last updated on January 31, 2015
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