Vertical distribution and feeding pattern of Euphausiacea (Crustacea) in the eastern Banda Sea (Indonesia) during the SE and NW monsoons

The vertical distribution of Euphausiacea (Crustacea) in theeastern Banda Sea (Indonesia) during the SE and NW monsoon seasonswas studied. In August 1984 and February/ March 1985, stratifiedday and night sampling was carried out between 0 and 500 m atfour stations. A total of 31 species was found, of which mostwere present in both monsoon seasons. Species with a high presencein samples and performing diurnal vertical migration in bothmonsoon seasons were Euphausia diomedeae, Euphausia pseudogibba,Thysanopoda monacantha, Thysanopoda iricus-pidaia and Nematoscelismicrops. Species with a high presence in samples showing nodiurnal vertical migration in both monsoon seasons were Euphausiasimilis, Nematobrachion boopis. Nematoscelis tenella, Stylocheironmaximum and Thysanopoda orientalis. The density of Euphausiaceaat the sampled stations was higher, but more heterogeneous,in the nutrient-enriched SE monsoon period than in the relativelynutrient-poor NW monsoon season, when densities were lower andmore similar. The vertical distributions and diurnal verticalmigration of species did not show a unanimous and strong responseto seasonal hydrographic differences. The day–night depthdistribution pattern of the Euphausiacea population in the upper500 m is largely the same in both seasons, with comparable migrationranges. Some species showed a somewhat upward shifted depthdistribution in the nutrient-enriched period. For mesopelagicand bathypelagic species especially, food resources were thenfavourable in the upper layers, as indicated by rare recordsof Thysanopoda crisiata. Analyses of stomach contents snowedmainly a nocturnal feeding pattern for the diurnal verticalmigrating species and a continuous feeding pattern for the non-migratingspecies.