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GLERL 2003 Milestone Reports
GLERL 2003 Milestone Home
GOAL 1: Protect, Restore and Manage Use of Ocean and Coastal Resources Through Ecosystem Management Approaches
OBJECTIVE: Increase use of physical-biological models for forecasting stock abundance.
Specific Strategy: Assess and predict fish populations by developing ecosystem models to improve Great Lakes fisheries management techniques.
Milestone: Model the disruption of food webs by invasive species with implications to fish populations.
Scientist: Dr. Doran M. Mason
Purpose: Early in the 20th century, the fish communities of the Laurentian Great Lakes were profoundly disrupted, and permanently changed, by a wave of vertebrate invaders: sea lamprey, alewife, and rainbow smelt. These disruptions were largely focused at the upper end of food webs, and, hence, traditional fishery models could be adapted to quantify the associated impacts. During the last 15 years, the Great Lakes have suffered a second wave of invasions featuring invertebrates: two species of dreissenids-zebra mussels (Dreissena polymorpha) and quagga mussels (D. bugensis)-and two predatory cladocerans-Bythotrephes cederstroemi) and Cercopagis pengoi). These four invertebrates are expected to disrupt, or have already disrupted, the fish communities in the Great Lakes in ways quite different from the earlier wave of vertebrate invaders. In contrast to the vertebrate invasion, invertebrate disruptions start at lower trophic levels and percolate up through the food web with potentially serious consequences for fisheries. The bottom-up effect on the food web eliminates the potential application and modification of traditional fisheries models to quantify and predict direction and magnitude of disruption.
Arguably an ecosystem level approach, which incorporates field studies and modeling, is necessary to quantify and eventually predict the impacts of these recent invertebrate invaders. Moreover, factors such as lake morphology, trophic status and the temporal sequencing of invasions, all of which differ among lakes, likely modify the magnitude of the invertebrate impact and the current state of food web change. There are many areas of research currently underway that emphasize field and dynamic modeling approaches. However, many of these studies focus only on a subset of the system and none of them evaluates and quantifies the current state of the entire food web before and after invertebrate invasion. What is required are techniques that synoptically evaluate and quantify the structure and flows in food webs across temporal (seasons and years) and spatial (trophic status, nearshore-offshore) gradients, and how changes in the food web, from invasive invertebrates, disrupt and change these structures and flows.
Our overall purpose is to take an ecosystem level approach and construct food webs for the Bay of Quinte Lake Ontario, Oneida Lake, and Lake Michigan across years (pre-invertebrate invasion and post invasion), and trophic status (e.g., concentrations of nutrients), and size of ecosystem to quantify how invertebrate invasions disrupted lake wide and regional food webs, and to eventual predict ecosystem change and fisheries impacts in response to species invasion. Specific to this milestone report, our purpose was to explore the application of new analytical techniques for quantifying change in the structure of Great Lakes food webs and the further development of analytical software (EcoNetwrk) for modeling/analyzing Great Lakes food webs.
Figure 1: Screenshot of EcoNetwrk analytical software click for full size image
Efforts: We have applied a technique recently developed social sciences, called cohesion analysis, to identify compartments within food webs. Compartments are analogous to ecological communities; the identification of these compartments then allows us to quantify and evaluate how ecosystems are organized and how invasive species may reorganize ecosystems. We are now in our second phase of developing the software EcoNetwrk that allows direct data entry as well as food web modeling and analysis.
Customers: Ultimately, the customers/beneficiaries of this project are the fisheries managers and recreational users of the Great Lakes through better-informed management of the fisheries. This will be realized through improved understanding of how invasive species disrupt food webs and our ability to predict how new species introductions may impact important fish populations. The immediate customers are researchers interested in predictive understanding of ecosystem level impacts of invasive species in large aquatic ecosystems.
Significance: Provide the ability to identify ecological compartments within the Great Lakes ecosystem and to quantify how compartments change in response to species invasions, and thus how energy flows up the food web to support the important fisheries. Changes in compartment structure and organization has implications for the direction of energy flow, and thus how much energy is available to support import fish species, such as salmon, in the Great Lakes. Significance of our software development is improved ability to do the food web modeling and making these tools available to other researchers and ultimately to fisheries managers that share similar interests.
Success: We have successfully applied cohesion analysis to aquatic food webs and have demonstrated its applicability towards quantifying structural and organizational changes in ecosystem function as a result of species invasions.
Next steps: To apply the new techniques toward quantifying the impacts of the recent invertebrate invaders on the ability of the Great Lakes to support important fish species. Moreover, we will continue development EcoNetwrk software for food web analysis.
Last updated: October 14, 2003 mbl