OBSERVATIONS ON BEHAVIOR AND DISTRIBUTION OF NATATOLANA-BOREALIS (LILLJEBORG) (CRUSTACEA, ISOPODA)

Natatolana borealis were collected with baited traps at two localities near Bergen, Norway in 1977-78 and 1991-96, and faunistic surveys car ried out with grab, detritus sledge and epibenthic sampler in Norwegia n waters, including the northern Norwegian Trough, from 1981 to presen t, and in Faroese waters in the years 1987-90. Catches of N. borealis by epibenthic sledge in the Norwegian Trough were significantly larger at night than in daylight. Laboratory observations and trap experimen ts indicate that feeding activity is regulated by in situ illumination and degree of hunger. The species appears to be an opportunistic omni vore scavenger and might use a combination of 'sit and wait' and 'swim across the current' foraging strategies. The content of the anterior hindgut averaged 42 % of the total body dry weight after unlimited acc ess to food for 24 h. A full gut enabled survival without further feed ing for > 6 months. The assimilation efficiency of N. borealis feeding on fish flesh was estimated to be > 90 %. Recent records of N. boreal is indicate a northern distribution limit at ca 70 degrees N on the co ast of Norway. At the Faroe Islands it was only found in water-masses dominated by Atlantic Water and not in water-masses dominated by the c older Arctic Intermediate Water or the cold Norwegian Sea Bottom Water . The usual temperature range of waters inhabited by N. borealis in th e East Atlantic is about 5-14 degrees C. It occurs in a wide range of sediments (from gravelly sand to fine silty clay) into which it burrow s.