Nearshore Community Characteristics Related to Shoreline Properties in the Great Lakes

Successful protection and restoration of Great Lakes nearshore ecosystems will likely rely on management of terrestrial resources along Great Lakes shorelines. However, relationships between biological communities and changing shoreline environmental properties are poorly understood. We sought to begin understanding the potential roles of shoreline geomorphological and land cover properties in structuring nearshore biological communities in the Laurentian Great Lakes. Despite high variability in densities (benthic macroinvertebrates and zooplankton) and catch per unit effort (CPUE, shallow water and nearshore fish) within and among lake areas, several biological community patterns emerged to suggest that nearshore aquatic communities respond to shoreline features via the influences of these features on nearshore substrate composition and stability. Benthic macroinvertebrate densities were not different between shoreline types, although they were generally lower at nearshore sites with less stable substrates. Shallow water fish CPUE and zooplankton densities were generally lower for nearshore areas adjacent to developed mid-bluff shorelines and sites characterized by less stable substrates. Larger fish CPUE appeared to be unresponsive to local shoreline and substrate properties of nearshore zones. The emergence of these patterns despite significant ecological differences among lake areas (e.g., productivity, community composition, etc.) suggests that shoreline development may have comparable influences on nearshore ecosystems throughout the Great Lakes, providing a terrestrialbased indicator of relative nearshore biological and ecological integrity. INDEX WORDS: Great Lakes, nearshore ecology, biological communities, shoreline land use. *Corresponding author. E-mail: [email protected] INTRODUCTION Great Lakes nearshore zones factor significantly in the life histories of many Great Lakes native fish species (Goodyear et al. 1982; Lane et al. 1996a,b), as well as providing important habitat for their prey (e.g., Jude and Tesar 1985, Evans 1992, Madenjian et al. 2002). Steedman and Regier (1987) referred to “centers of organization” within nearshore areas that provide essential fish habitat, both in terms of physical features and consumable resources (Hayes et al. 1996), that are of greater importance than their limited spatial extent would suggest. However, nearshore areas are particularly susceptible to anthropogenic stressors because they serve as an interface between terrestrial and open-water environments. As such, human activities along shorelines may directly influence nearshore areas through exchanges of materials such as sediment, nutrients, and chemical pollutants. However, the degree to which shoreline activities influence nearshore habitats and biological communities is poorly understood. Shoreline hardening to prevent natural erosion processes alters nearshore littoral transport of substrates, eliminates shoreline migration as Great 114 Goforth and Carman Lakes water levels change, and reduces aquatic habitat diversity (Steedman and Regier 1987, Edsall and Charlton 1997). In addition, straightened shorelines lose structural irregularities that drive variations in alongshore currents and local substrates. Therefore, the type, distribution, and stability of substrates within nearshore areas is expected to change as shoreline features are altered by human activities. The distribution and availability of different substrate types contributes to habitat heterogeneity, a significant factor in determining fish community structure and production (Eadie and Keast 1984, Benson and Magnuson 1992, Leslie and Timmins 1993). Biological uses of these habitats are directly related to available surface area, pattern, distribution, and relative stability of substrates comprising the lakebed within the nearshore zone (Mackey and Liebenthal 2005). As nearshore substrate properties (e.g., composition and stability) are altered by nearshore-shoreline interactions, community structure is expected to change as well. Given the importance of nearshore areas to Great Lakes fauna of multiple taxonomic groups, changes in community structure could have dramatic effects on Great Lakes fisheries and productivity over time. Understanding nearshore community responses to shoreline features that drive nearshore substrate composition, distribution, and stability will contribute greatly to managers’ abilities to make informed decisions about shoreline development and other activities that may affect these ecosystems. In an effort to begin understanding the role of shoreline features in Great Lakes nearshore ecology, we conducted biological community studies of six Great Lakes nearshore areas associated with varying local shoreline geomorphology and human development. We sought to identify community and functional/taxonomic group patterns associated with regional (lake area) and local shoreline properties via density measurements of major taxonomic groups. We hypothesized that densities of native fish, benthic macroinvertebrates, and zooplankton would be higher at nearshore areas associated with lower levels of shoreline development and structure placement (i.e., unique shorelines) compared to heavily engineered, mid-size bluff (< 30 m tall) shorelines (i.e., mid-bluff shorelines). We expected that these patterns would remain consistent among several lake areas of the basin, including southern Lake Erie (SLE), eastern Lake Michigan (ELM), and western Lake Michigan (WLM). We also hypothesized that native biological community density measures would be higher in nearshore areas with relatively stable vs. highly unstable substrates. METHODS