Disappearance of the Amphipod 'Diporeia' spp. in the Great Lakes: Workshop Summary, Discussion, and Recommendations. Held in October 2006.

摘要

A workshop was held in October, 2006 to discuss population status and causes of the disappearance of the benthic amphipod Diporeia spp. in the Great Lakes, and to provide recommendations for future research. Recent surveys indicate that Diporeia continues to decline in Lakes Michigan, Huron, and Ontario, but surveys in Lake Superior are con- flicting. One data set shows that the population in Lake Superior is declining in offshore regions (> 90 m) but not in nearshore regions (< 90 m). Other data sets show that the population is stable throughout the lake. Reasons for this discrepancy were not resolved. In the other lakes, Diporeia are now rare or completely gone at depths < 90 m, and are declining at depths > 90 m. Declines at the latter depths are preceding the expansion of Dreissena bugensis (quagga mussel) from shallow to deeper regions. While there is a strong negative relationship between Diporeia and Dreissena in the Great Lakes, Diporeia remains abundant in the Finger Lakes, New York, despite the long-term presence of Dreissena. There are areas in the Great Lakes where Diporeia seemed to persist but are now declining, indicating that environmental conditions do play a mitigating role to some extent. While there was agreement that Dreissena was the cause of the disappearance of Diporeia in the Great Lakes, a survey of workshop participants indicated no clear consensus on potential mechanisms for the negative response. The most popular theories were food limitation directly or indirectly related to dreissenid filtering activities, a toxic by-product associated with dreissenid biodeposits, and an introduced pathogen/disease. Based on previous field surveys and laboratory experiments, there are inconsistencies in each of these theories, which may imply a multitude of causative factors whose relative importance may vary depending on specific environmental conditions. Given the potential for multi-stressors, techniques that provide genomic or protein profiles offer promise in defining a specific cause. Included among the recommendations for future research are continued monitoring of Diporeia in the Finger Lakes along with an assessment of conditions that allow it to persist, experiments to further define a dreissenid by-product that negatively impacts Diporeia, the development of genomic and proteonic approachesspecific for Diporeia, a better definition of taxonomic status, and further efforts to characterize/ resolve conflicting trends in offshore populations in Lake Superior.