Suprabenthic gradients of swimming activity by cold-water gammaridean amphipod Crustacea over a muddy shelf in the Gulf of Saint Lawrence

From May to October 1961-62 and 1969, suprabenthic sampling above homologous, uniformly deep (119 m), cold (? = 0.8"C), and muddy grounds of Baie des Chaleurs, Gulf of Saint Lawrence, yielded 82 gammaridean amphipod species belonging to 27 families.Fifty-one species regarded as suprabenthic are grouped into 7 categories according to amplitude, intensity and regularity of their swimming behavior.The 14 Oedicerotidae account for 88 % of suprabenthic amphipods, whereas in the endobenthos the lysianassid Paratryphosites abyssi is dominant (53 %), the Oedicerotidae (3.3 %) being only the sixth most important family.True suprabenthic species typically swim to at least 3.7 m above the bottom.Permanent members of the suprabenthos, including large predatory species, a carrion feeder, and many detritivores, are thought to forage in the suprabenthic layer.