Citation:

Mehler, K., L. Burlakova, A. Karatayev, AND J. Scharold. Major findings from the CSMI benthic macroinvertebrate survey in Lake Superior in 2016 with an emphasis on temporal trends. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-18/118, 2018.

Impact/Purpose:

Benthic macroinvertebrates are an important component of the food web of Lake Superior and are used as indicators of ecological condition. A lakewide nearshore survey of benthic macroinvertebrates, compared with data from previous surveys, provides crucial information on their spatial and temporal variability.

Description:

As part of the Coordinated Science and Monitoring Initiative (CSMI) in Lake Superior in 2016, a lake-wide benthic survey was conducted to assess the status of the benthic macroinvertebrate community with primary focus on the native amphipod Diporeia, Oligochaeta, Chironomidae, and Sphaeriidae. In general, the nearshore benthic community was relatively stable in terms of abundance and composition between 1994 and 2003 (Scharold et al. 2009). The amphipod Diporeia was the dominant taxa of the benthic macroinvertebrate community in terms of density and biomass and was present at 99% of stations occupying the entire depth range sampled (18 to 139 meters). In 1994, nearshore Diporeia abundance ranged from 370 to 5507 m-2 with a mean (± SE) of 1,937 ± 224 m-2 and exceeded the ecosystem objective of at 220-300 individuals m-2 for nearshore waters established by the Great Lakes Water Quality Agreement (GLWQA) of 1978 (IJC 1978). In 2000, mean Diporeia abundance dropped by 35% and ranged from 7 to 2,782 m-2 with a mean (± SE) of 1,301 ± 141m-2. Due to the drop in abundance, 11% of the station did not meet the GLWQA requirements. Although the decline in Diporeia between 1994 and 2000 was significant, the severe declines in Diporeia populations that have been observed in the lower Great Lakes (Dermott 2001, Nalepa et al. 2006, Watkins et al. 2007, Nalepa et al. 2009) are not evident in Lake Superior. In 2003 Diporeia abundance returned to levels similar to those in 1994 indicating that Diporeia population in Lake Superior showed no progressive decline compared to other Great Lakes within the same time period. In 2016 a survey was conducted to examine the entire benthic community at randomly chosen nearshore stations, as well as at stations that were sampled previously in 1994-2003, which allowed a comparison with previous studies to assess changes of the nearshore benthic community in Lake Superior since 2003. Lake-wide trends in the entire benthic community have recently been examined in Lake Michigan (Nalepa et al. 2009), Lake Huron (Nalepa et al. 2007), Lake Ontario (Birkett and Lozano 2015), and Lake Erie (Burlakova et al. 2014). This report provides a summary of recent trends of major taxonomic groups (i.e. Oligochaeta, Sphaeriidae, and Chironomidae) with particular emphasize on Diporeia. More detailed analyses and discussion of trends, spatial patterns, and community composition, including comparisons to lake-wide surveys in the other Great Lakes, will be provided in other publications.

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