Pelagic Amphipoda of the Belle Isle Strait Region

Abstract

The distribution of certain pelagic Amphipoda taken in the Belle Isle strait region during the summer of 1923 is correlated with ocean currents, light intensity and size of individuals. Hyperoche medusarum, Themisto libellula and Pseudalibrotus glacialis are index species of the cold Labrador current in the area. Hyperia galba and H. medusarum are presumably also cold water indicators. Themisto abyssorum in sizeable numbers, and Calliopius laeviusculus are related to waters of the gulf of St. Lawrence. Themisto libellula, T. compressa form compressa and T. compressa form bispinosa are more numerous, while T. abyssorum is less numerous at the surface during daylight than during darkness. Part of the breeding season of T. compressa and T. abyssorum occurs in the area during August and September, when the young of both species are much more numerous than the adults, particularly at the surface. A new southern limit of distribution for P. glacialis is established. The known distribution of the tropical genus Phronima is extended into the gulf of St. Lawrence.