Copepod limnocalanus macrurus mating in relation to vertical migrations and aspects of feeding rates in the Bothnian Sea (Baltic Sea)

The studies of calanoid copepod Limnocalanus macrurus feeding rates and mating related to vertical migration were conducted in October 2005 in the Bothnian Sea. The monocyclic copepod Limnocalanus macrurus develops mostly to adult and larger copepodites stages in autumn and these stages were investigated. Bothnian Sea is a brackish-water basin in Baltic Sea with comparatively big depth therefore Limnocalanus macrurus which prefer to live in deep and cold water is more abundant in this Baltic Sea part. Recent observations in the Bothnian Sea showed that Limnocalanus macrurus performs diel vertical migrations and adults approve stricter tendency to stay under thermocline layer at night than copepodite stages. Adult migration behaviour could be connected with Limnocalanus macrurus reproduction character, but the existing information about the species reproduction ecology is very scarce. Therefore the task of the investigation was to find relationship between mating, reproduction and vertical migration of Limnocalanus macrurus in the Bothnian Sea. Sampling was done in 125 m deep station after every 3 hours during day and night above, inside and below the thermocline layer. The results show the daily distribution of Limnocalanus macrurus adults and larger copepodites. As the diel vertical migrations are connected also with daily feeding patterns, the feeding rates were examined by determining gut clearance rate.