Benthic and pelagic secondary production in Lake Erie after the invasion of Dreissena spp. with implications for fish production

Benthic and pelagic secondary production were measured at nearshore and off shore sites in the western, west-central, and eastern basins of Lake Erie i n 1993 to determine the relative importance of benthic and pelagic foodwebs to the fish community after dreissenid colonization. Benthic biomass incre ased greatly between 1979 and 1993 because of the presence of dreissenids, and > 90% of benthic production in 1993 came from dreissenids. Biomass of " other" benthos (excluding unionids and dreissenids) did nos decline. Dreiss enid production was in addition to, and nor at the expense of "other" benth ic production. Zooplankton production was close to or within the 95% confid ence interval of that predicted from primary production (photosynthesis) ba sed on the relationship described by Makarewicz and Likens (1979). Deviatio ns from this relationship were correlated with summer zooplankton mean leng th, suggesting that planktivory was an important factor in the regulation o f zooplankton production in the lake. Dreissenids therefore impact zooplank ton production by reducing algal biomass and primary production particularl y in unstratified regions, by decreasing rotifer abundance and hence biomas s and production, and by producing veligers which contribute 10% to 25% to zooplankton production. Potential fish biomass which could be supported by the benthic and pelagic foodwebs was estimated from empirical equations. The benthic food chain cou ld potentially support more fish biomass than the pelagic food chain in all basins in 1993, even if dreissenids were excluded from the calculations.