Assessment of shoreline restoration using macroinvertebrates in a Great Lakes Area of Concern

Macroinvertebrate community assemblages were examined in three areas of the littoral zone of an impacted, drowned river mouth lake in west Michigan, USA. Muskegon Lake has an extensive history of environmental abuse, resulting in its listing as a Great Lakes Area of Concern. A multi-organizational, shoreline restoration initiative was started in 2009 and completed in 2012. Despite pre- and post-restoration monitoring of water quality, fish assemblages, and macrophytes, no studies had examined the shifts in the littoral zone macroinvertebrate community. Using Hester-Dendy samplers, we collected macroinvertebrates monthly in submergent, emergent, and open macrophyte zones, at two restored sites and one reference site from August 2018 to October 2019. No pre-restoration samples were collected at these sites but we could examine the changes in restored vs. reference sites. In total, 22,931 individuals were observed, with Gammarus spp., Echinogammarus spp., Chironominae, and Dreissena polymorpha being among the most abundant taxa. NMDS results revealed overlap among macroinvertebrate communities between the two restored sites and separation from the reference site, with some overlapping seasonal differences and communities influenced by macrophyte habitat type. Principal components analysis revealed that the environmental factors were strongly influenced by seasonal changes and drove habitat-level differences, rather than spatial variations among sites. Our results indicate that although the macroinvertebrate community composition at the restored sites differed from that at the reference site, the macroinvertebrate assemblage at each site was dominated by tolerant generalist species. Pollution-sensitive macroinvertebrate taxa may have been reduced or eliminated in the lake due to decades of environmental abuse. Periodic monitoring is recommended to determine if these sensitive taxa return, as Muskegon Lake conditions continue to improve.