Life after death in Lake Erie: Nutrient controls drive fish species richness, rehabilitation

We explored the recent (1969-1996) dynamics of fish communities within Lake Erie, a system formerly degraded by eutrophication and now undergoing olig otrophication owing to phosphorus abatement programs. By merging bottom tra wl data from two lake basins of contrasting productivity with life-history information (i.e., tolerances to environmental degradation, diet and temper ature preferences), we examined (1) the relationship between system product ivity and species richness, (2) whether fish communities are resilient to e utrophication, and (3) whether oligotrophication necessarily leads to reduc ed sport and commercial fish production. Reduced phosphorus loading has led to fish community rehabilitation. In the productive west basin, six specie s tolerant of eutrophy (i.e., anoxia, turbidity) declined in abundance, whe reas the abundance of three intolerant species increased through time. In t he less productive central basin, although only one tolerant species declin ed, four species intolerant of eutrophic conditions recovered with oligotro phication. These differential responses appear to derive from dissimilar me chanisms by which reduced productivity alters habitat and resource availabi lity for fishes. Specifically, enhanced bottom oxygen, combined with reduce d biogenic turbidity and sedimentation, likely drove the loss of tolerant s pecies in the west basin by reducing detrital mass or the ability of these species to compete with intolerant species under conditions of improved wat er clarity. In contrast, reduced bottom anoxia, which enhanced availability of cool- and cold-water habitat and benthic macroinvertebrate communities, appears important to the recovery of intolerant species in the central bas in. Ultimately, these productivity-induced shifts caused species richness t o decline in Lake Erie's west basin and to increase in its central basin. B eyond confirming that unimodal models of productivity and species diversity can describe fish community change in a recovering system, our results pro vide optimism in an otherwise dismal state of affairs in fisheries manageme nt (e.g., overexploitation), given that many recovering intolerant species are desired sport or commercial fishes.