The Distribution of Crustacean Zooplankton in Northern Ontario, Canada

The occurrence of crustacean plankton species was investigated in 337 lakes widely distributed across the northern portion of Ontario, Canada. General east to west patterns observed included increases in the occurrence of Chydorus cf. sphaericus (O. F. Muller) and Acanthocyclops vernalis (Fischer), disappearance of Eubosmina longispina (Leydig) and Eubosmina tubicen (Brehm) and generally reduced occurrence of Cyclops scutifer Sars and most daphnids except Daphnia galeata mendotae Birge and Daphnia retrocurva S. A. Forbes. Along a south to north gradient, the occurrence of Leptodiaptomus ashlandi Marsh increased greatly, Tropocyclops prasinus mexicanus Kiefer became very rare and Daphnia middendorfiana Fischer appeared in a large number of lakes. Secondary south to north patterns included increased occurrence of Leptodora kindtii (Focke), Sida crystallina (O. F. Muller)