Members of the family Ameronothridae inhabiting marine littoral environments show periodical vertical changes of population densities in the field. The vertical migration is characterized by intermittent locomotory activity, the rhythm, direction and intensity of which are dependent on tidal as well as light changes in the littoral of the North Sea, and solely on light changes in the littoral of the Baltic.Adult specimens collected along the coast of the North Sea with strong vertical tides perform under laboratory conditions vertical migrations with a spontaneous period of 24.6 hrs. Juvenile specimens show no migratory activity.The influence of the tides on vertical migration can be demonstrated by comparing populations from localities with different tides and by analysing those locomotion periods which are synchronized with high tide.The amplitude of vertical migration in the field is influenced also by the duration of submersion. Migration is further influenced by light changes. Specimens held in total darkness do not migrate, and experiments with populations collected along the coast of the Baltic with only moderate tides demonstrate clearly that vertical migration of these populations is based on light-dark changes.Studies on phototaxis revealed that adult specimens react positively whereas juveniles were quite indifferent.
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