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II. Zooplankton. Summary from Origi Bay of Quinte Remedial Action Plan Assessment of the State of Impairment of Beneficial Uses: II. Zooplankton. Summary from Original Document Prepared for Fisheries and Oceans Canada and Environment Canada by Ora E. Iohannsson' and Ken H. Nicholls' 'Great Lakes Laboratory for Fisheries and Aquatic Sciences Department of Fisheries and Oceans 867 Lakeshore Rd. Burlington, ON L7R4A6 'S-15 Concession I, RR # 1, Sunderland, Ontario LOC IRO Lake Ontario's Bay of Quinte has been identified a.s one of 42 Areas ofConcem in American and Canadian waters of the Great Lakes for which a Remedial Action Plan (RAP) is required as directed under the bi-national GreatLakes Water Quality Agreement. Most aquatic ecosystem problems in the Bay of Quinte are related to eutrophication caused by excessive nutrient loading and to degradation ofthe fish community through elimination/depression oftop predatory species and invasion of exotic species. These bottom-up and top-down forces have resulted in altered biological communities. Eutrophication impacts zooplankton communities in several ways: it can alter habitat conditions, food quality and feeding, and predation patterns of other interacting biotic components ofthe aquatic system. Zooplankton community structure is often altered as a result. Similarly, altered fish communities, especially those where planktivorous fish become dominant, reduce individual mean size and grazing capability of the zooplankton community as well as change community structure. Much progress has been made in the last 25 years in reducing point-source loading of phosphorus in order to rehabilitate the Bay of Quinte. Fish communities resurged with the development of the walleye and lake whitefish populations, and the decline of white perch in the 1980s. Further changes have occurred in the late 1990s with the decline in lake whitefish, redistribution of walleye and resurgence of yellow perch, all associated with the colonization of Lake Ontario and the Bay of Quinte by dreissenid mussels. The major purpose of this report is to assess the Beneficial Use Status of the zooplankton in the Bay of Quinte by examining long-term trends in the crustacean zooplankton community with emphasis on those changes that may be related to rehabilitation of the Bay of Quinte ecosystem and to the recent (1995) establishment of zebra mussels in the bay. A variety of data analysis approaches utilizing both univariate and multivariate methods have been applied to the problem. An integral part of this assessment was the inclusion of zooplankton data from three other reference locations that may serve as analogues for a less perturbed upper Bay of Quinte. It is suggested that the reference location zooplankton communities can thus serve as restoration targets for the upper bay. Comparisons of community structure have been supplemented with comparisons of zooplankton biomass, mean size and ratios of predatorlherbivore biomass 2 which reflect patterns of energy flow through the system. This assessment uses a 24-year data series collected under Project Quinte, a multi-agency collaborative study of long­ term change in the Bay of Quinte. Sixty species of crustacean zooplankton have been identified in the Bay of Quinte samples, including 41 cladoceran species, 10 cyclopoid .~ copepod species and 9 calanoid species. Most common were Bosmina longirostris, Ceriodaphnia lacustris, Chydorus sphaericus, Daphnia galeata mendotae, D. retrocurva, Diaphanosoma birgei, Cyclops vernalis, Diacyclops thomasii, Mesocyclops edax and , Tropocyclops extensus. The distribution of zooplankton species in the Bay of Quinte reflects a spatial gradient in eutrophy and habitat structure (water depth, temparature and thermal structure of the water column) from the shallow, warm, eutropic, upper bay to the deep (32 m), thermally-stratified, mesotrophic lower bay. A significant change in species richness over time was observed only at station (HE) in the middle of theBay of Quinte. Here, reductions in species richness averaged 0.23 species/year, with a total reduction in species number of21 % between 1982 and 2000. Very low species numbers (11 and 13) were recorded during 1992 at Stations Band HB, respectively, which likely was related to record low water temperature during that year (although the mechanism is unclear). The zooplankton community structure showed considerable spatial dissimilarity as well as temporal change. Multivariate analyses of species composition illustrated how zooplankton community composition shifted firstly with the decline in phosphorus loading and concentrations (1979-1981/2), secondly with the change in the fish community (1982/3-1991), thirdly with the climatic event (cold spring in 1992) caused by the eruption of Mount Pinatubo in 1991 (effects observed only in 1992 (Station C) or later, 1994 (Station B», and fourthly with the invasion of dreisenids (1995-2000). At each of these junctures, the zooplankton community composition changed position in "community" space. At these same junctures changes in community function were also observed. It should be noted that 2000 was also an unusual year and the reasons for these differences are not currently understood. The response ofthe zooplankton community to decreases in P loading are difficult to distinguish due to changes in the fish community in the 1980s. Changes consistent with decreases in P were declines in the densities of Chydorus sphaericus, Eubosmina coregoni and Cyclopos vernalis. Cluster analysis also indicated that the zooplankton' 3 community in later years at Station B was similar to that at Station HB in the early years. of the study: HB always had lower total phosphorus levels than Station B. Declines in P­ loading appeared to· have relatively more impact at Station C than the other sites. Comparisons of zooplankton community structure between the pre-phosphorus control .~ years of 1975-76 and the more recent pre- and post Dreissena years revealed that the differences were most significant at Station C and least significant at Station B. Increases in the biomass of piscivores (walleye, large white perch) in the bay in the early 1980s were associated with dramatic changes in the zooplankton community. Total zooplankton biomass, Daphnia biomass, and mean individual length increased with the increase in piscivore biomass. Some zooplankton species increased while others decreased. In total, 33 taxa significantly increased over the 1975-1994 time period, while 18 taxa decreased. Significant increases were found for Daphnia galeata mendotae, and decreases for Leptodora kindtii at all three sampling stations. Other trends included increased densities of benthic cladocera, Bosmina longirostris, total Daphnia sp. and Holopedium gibberum in the middle and lower bay, but not in the upper bay. Daphnia pulicaria, Skistodiaptomus oregonensis, benthic copepods, total adult calanoids and Mesocyclops edax all increased in the upper and middle bay, but not in the lower bay. Chydorus sphaericus, and total calanoid copepodids declined in the middle and lower bay, but not the upper bay, and Diaphanosoma birgei decreased in the upper and middle bay over the 1975-1994 period. Zebra mussels (Dreissena) invaded the Bay of Quinte in the mid-1990's; 1995 is considered to be the earliest year of a significant Dreissena population in the bay. With the arrival of dreissenids, zooplankton total biomass decreased at all three sites even though zooplankton mean length did not change. This indicates that the decline in biomass was not related to changes in the level of predation on zooplankton by fish. The declines are most likely related to effects of dreissenids on food resources. The ratio of predatory to total zooplankton biomass also decreased at all sites with a decrease in the percentage of cyclopoids in the communities. Thus the relative importance of the "grazer pathway" in the pelagic foodweb increased and the relative importance of the microbial loop, which is dependent on predation by zooplankton to transfer energy up the foodweb to fish from ciliates and rotifers, decreased. 4 In tenns of specific species effects - only two crustacean zooplankton species or taxon groups at Station B, three at Station HB and four at Station C showed significant differences between pre- and post Dreissena 6-year time periods (1989-1994 vs 1995- 2000); however it has not been possible to detennine conclusively that the observed .~ changes in any of these taxa were caused by the establishment of Dreissena. The best case for a Dreissena effect might perhaps be made for those zooplankton taxa that showed a significant change in the 6-year pre- and post Dreissena comparisons, following the absence of a significant longer tenn trend in the 1975-1994 data series .. Taxa fitting this condition include declines in Chydorus sphaericus at Station B (-67 %), Daphnia pulicaria at Station C (-94 %), total cyclopoid copepodids at Stations B (-67 %) and C (-57 %), and increases of317 and 186 %, respectively, at Stations HB and C, in total calanoid nauplii. The multivariate data analysis revealed an altered and less stable community structure after dreisenids invaded; also, different species were involved in these changes than those observed with decreases in P-Ioading. Comparisons of community structure between the reference lakes and the upper bay after dreissenid arrived (1995-2000), indicated that a trend towards a less perturbed state in the upper bay, would have to include reductions in the densities of Eubosmina coregoni, Daphnia retrocurva,
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