Subtidal Hydroids (Cnidaria) of Northumberland Strait, Atlantic Canada, with Observations on Their Life Cycles and Distributions

Hydroids were examined in collections from a biological survey of Northumberland Strait undertaken by Fisheries and Oceans Canada from June to August 1975. No investigations have been undertaken previously on hydroids of the study area. Forty-eight species referable to 12 families were present in the samples, with Sertulariidae dominating in both numbers of species (12) and frequency. Gonophores were found in 30 of the species. As usual in hydroids of higher latitudes, a majority of those represented do not have a medusa stage in their life cycle. Gonophores in 42 of the 48 species are known to be fixed sporosacs while free medusae or medusoids occur in only six. Two major species groups were distinguished in a numerical analysis of hydroid species/station data. One of these groups included the three most ubiquitous species ( Calycella syringa , Hydrallmania falcata , Sertularia latiuscula ) together with 15 others most prevalent in samples from shallower ( 20 m) and mostly colder waters. Two species ( Lafoeina tenuis , Halecium lankesteri ) are new to the Atlantic coast of North America. Eight others ( Bougainvillia sp., Eudendrium dispar , Eudendrium ramosum , Cuspidella humilis , Opercularella pumila , Halecium scutum , Halecium sessile , Diphasia fallax ) are reported in the southwestern Gulf of St. Lawrence for the first time. The subtidal hydroid fauna in open waters of Northumberland Strait is a cold-water assemblage typical of the boreal zone in the western North Atlantic, and no relict warm-temperate species were found.