Benthic Macroinvertebrates as Indicators of Environmental Degradation in the Southern Nearshore Zone of the Central Basin of Lake Erie

The benthic macroinvertebrates of the central basin of Lake Erie were sampled with a Ponar grab in the summers of 1978 and 1979 along a 155-km reach of the nearshore zone (≤ 12 km offshore) in Ohio, U.S.A., at depths of less than 20 m. The major groups and their most abundant species were, in order of overall abundance, Oligochaeta (Limnodrilus hoffmeisteri, L. cervix-L. claparedeianus group, L. maumeensis), Sphaeriidae (Pisidium casertanum, P. henslowanum, Sphaerium corneum, Musculium transversum), and Chironomidae (Procladius sp., Chironomus spp.). The average abundance of oligochaetes in the harbors was 21,000 individuals m^?2 in 1978 and 12,700 m^?2 in 1979, compared with 1,500 m^?2 and 1,200 m^?2, respectively, in the areas outside of harbors. Comparison of the macrobenthic assemblages with those in other regions of the Great Lakes, using several numerical indices as well as indicator species distributions, indicated that the general area of the nearshore zone outside of harbors possesses a moderate degree of organic enrichment, with a gradient of decreasing pollution in an offshore direction. The harbors appeared to be severely degraded, as reflected by the high densities of oligochaetes and the almost complete absence of all but the most pollution-tolerant species. The documentation of species distributions will enable future assessments of changes in the nearshore benthic communities.