John C. H. Carter

Factors contributing to coexistence of Chaoborus flavicans and C. punctipennis (Diptera, Chaoboridae) in a small meromictic lake

In Crawford Lake, a small meromictic water body in southern Ontario, Canada, the life cycles of planktonic Chaoborus flavicans and C. punctipennis were out of phase by about two months, the former pupating from mid May through mid June and the latter from July through September. C. flavicans possibly produced a second annual generation. Fourth instars of both species were strong diel migrators and occupied similar strata at most times. C. punctipennis fourth instar diet consisted almost entirely of rotifers. C. flavicans ate rotifers but fed heavily also on daphnids in May and August. C. punctipennis fourth instars showed little growth until early spring, possibly owing to a sparseness of rotifers, then grew rapidly until pupation. C. flavicans had a slow, but relatively constant growth rate at all times during the open water season, presumably because its greater mouth gape allowed it a wider range of food items.

Seasonal and Horizontal Distributions of Planktonic Crustacea in Georgian Bay and North Channel, 1974

Samples taken from Georgian Bay and North Channel from April to December, 1974, were analyzed with respect to species composition and abundance, and seasonal and horizontal distribution. Eleven species of Cladocera and 12 of Copepoda were found. Cyclops bicuspidatus thomasi comprised more than 50% of all planktonic Crustacea. Warm surface waters accumulated in the northern and eastern parts of Georgian Bay and the eastern end of North Channel in late spring and early summer probably contributed to the high abundance of cladocerans in those regions during that period. Horizontal distributions of both cyclopoid and calanoid copepods showed no positive relationship to temperature and were probably a consequence of transportation by water currents. Mean summer abundance of planktonic Crustacea in Georgian Bay and North Channel in 1974 was slightly higher than that in Lake Superior but much lower than that in Lake Huron during 1968.

The Oligochaeta, Polychaeta and Nemertea of Parry Sound, Georgian Bay

Abstract During a study of benthic invertebrates in Parry Sound, Georgian Bay, at least 31 species of Oligochaeta and one species each of Polychaeta and Nemertea were collected. On firm clay, sand and gravel substrates, throughout the range of depths sampled, the lumbriculid Stylodrilus heringianus was the dominant oligochaete. On silt substrates five species of Tubificidae dominated the deep water oligochaete community while at shallow sites a number of other species including naidids, a polychaete, a new species of nemertean, Peloscolex ferox and other tubificids were present.

Diacyclops Nanus (Cyclopoida:Copepoda), A New Record from the Saint Lawrence Great Lakes

Diacyclops nanus (Sars), a cyclopoid copepod rare in North America, is recorded for the first time from the Saint Lawrence Great Lakes and for the second from Canada as a whole.