Recent Changes in the Phytoplankton of the Bay of Quinte, Lake Ontario: the Relative Importance of Fish, Nutrients, and Other Factors

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Abstract
A 50% reduction in phosphorus loading to the upper Bay of Quinte (Lake Ontario) from municipal sources in 1977 was followed by a major decline in phytoplankton biomass in 1978. However, by 1984–85, biomasses again approached those of the pre-phosphorus control period, despite continued low phosphorus loadings. No major shifts in phytoplankton composition occurred; domination by the diatoms Melosira and Stephanodiscus spp. and the blue-green algae Anabaena and Aphanizomenon spp. has continued. Highly significant positive correlation coefficients (r = 0.92–0.98) were found for phytoplankton — fish relationships during both the pre- and postphosphorus removal periods which coincided with pre- and postdie-off periods of white perch (Morone americana) and alewife (Alosa pseudoharengus). For the entire 16-yr period of data collection, a multiple regression model fitting upper bay phytoplankton biomass (with an adjusted R2 of 0.83) was developed with five input variables. White perch biomass alone explained more than 50% of the variance in the model. It is hypothesized that trophic interactions among other biotic components in the Bay of Quinte may be very important in controlling phytoplankton biomass.