Bm. Balino et Dl. Aksnes, WINTER DISTRIBUTION AND MIGRATION OF THE SOUND-SCATTERING LAYERS, ZOOPLANKTON AND MICRONEKTON IN MASFJORDEN, WESTERN NORWAY, Marine ecology. Progress series, 102(1-2), 1993, pp. 35-50
Sound scattering layers (SSLs) and vertical distribution of zooplankto
n and micronekton in Masfjorden, western Norway, were studied in Janua
ry 1988. Two characteristic SSLs were found in the deepest fjord basin
(bottom depth 490 m) while single scattering layers were observed in
shallower basins (depths <300 m). The SSLs performed diurnal vertical
displacements, exhibiting migrational speeds of up to 90 m h-1. The ad
justment of the SSLs' day depth was directly proportional to the rate
of change in the logarithm of surface light and inversely proportional
to the extinction coefficient of the water. Large horizontal differen
ces in biomass in the fjord are related to a combination of advection
and changes in migrational behaviour. Feeding activity of the micronek
ton was higher during light hours. Euphausiids of the deepest basin we
re mainly feeding on detritus while those in the innermost part of the
fjord seemed to be preying upon copepods. The observed vertical distr
ibution of the zooplankton and micronekton were examined in relation t
o mode of feeding (visual vs tactile), trophic level (omnivory vs carn
ivory), size (small vs large), and food type and availability.