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Status of the amphipod Diporeia spp. in Lake Superior, 2006-2016
Citation:
Scharold, J. AND T. Corry. Status of the amphipod Diporeia spp. in Lake Superior, 2006-2016. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 47(4):1033-1039, (2021). https://doi.org/10.1016/j.jglr.2021.04.013
Impact/Purpose:
Amphipods of the genus Diporeia play an important role in the Great Lakes ecosystem, and they have been selected as an indicator of ecological condition for Lake Superior by the 1978 Great Lakes Water Quality Agreement. During the last few decades, their populations have declined in Lakes Ontario, Erie, Michigan and Huron, which has raised concerns about their status in Lake Superior. To assess the status of Diporeia populations in Lake Superior, we conducted a series of lake-wide probability-based surveys in 2006, 2011, and 2016. Our results showed higher densities in the nearshore zone (<100 m deep) than offshore, with no statistically significant difference in lake-wide average density between years. The study provides information on the variability in Diporeia populations regionally and over time, which can be used to further refine monitoring designs and improve our ability to detect trends in Diporeia populations and thus the health of the Great Lakes. The survey design developed and demonstrated in this study can be used by monitoring and management agencies, including the Great Lakes National Program Office and States, to obtain unbiased estimates of benthos and other ecological endpoints to equip resource managers with the information required to make scientifically defensible management decisions.
Description:
The amphipod Diporeia spp. has historically been an important component of the benthic food web of the Laurentian Great Lakes. Its population density has been selected as an indicator of ecological condition for Lake Superior. To assess the status of Diporeia in Lake Superior, we used a probability-based lake-wide survey design to obtain estimates of Diporeia density and biomass in 2006, 2011 and 2016. A ponar grab was used to collect Diporeia at 50-53 sites each year, with approximately half in the nearshore (<100 m depth) region of the lake and half in the offshore. The mean area-weighted lake-wide density was 395 + 56 m-2 (mean + SE) in 2006, 756 + 130 m-2 in 2011, and 502 + 60 m m-2 in 2016. For all years, both density and biomass were greater in nearshore than offshore strata. The densities for 2006-2016 are 3-5 times higher than those reported from a lake-wide survey conducted in 1973 by the Canada Centre for Inland Waters (CCIW). The severe declines in Diporeia populations observed in the other Great Lakes during recent decades have not occurred in Lake Superior. further research is needed to understand spatial and temporal variability of Diporeia populations in Lake Superior. and enhance the utility of Diporeia density as an indicator.
