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 offshore sites in the western, west-central, and eastern basins of Lake Erie in 1993 to determine the relative importance of benthic and pelagic foodwebs to the fish community after dreissenid colonization. Benthic biomass increased 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. Dreissenid production was in addition to, and nor at the expense of "other" benthic production. Zooplankton production was close to or within the 95% confidence interval of that predicted from primary production (photosynthesis) based on the relationship described by Makarewicz and Likens (1979). Deviations from this relationship were correlated with summer zooplankton mean length, suggesting that planktivory was an important factor in the regulation of zooplankton production in the lake. Dreissenids therefore impact zooplankton production by reducing algal biomass and primary production particularly in unstratified regions, by decreasing rotifer abundance and hence biomass 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 could potentially support more fish biomass than the pelagic food chain in all basins in 1993, even if dreissenids were excluded from the calculations.