Nocturnal swimming of gammaridean amphipod and cumacean crustacea in Masfjorden, Norway

Vertical migration patterns in deep-living suprabenthic amphipods and cumaceans were studied by pelagic sampling. The amplitude of the vertical migrations was generally small (< 15–20 m above bottom). Nocturnal swimming was mainly restricted to the first part of the night. Ichnopus spinicornis differed from the general pattern: pelagic catches increased towards the latter part of the night, and the species was found far up in the water column. It is speculated that small amplitudes and short durations of vertical migrations may represent a trade-off between advantages of short distance dispersal (within habitat) and disadvantages of long distance dispersal (out of habitat).