engleski

Evidence of ontogenetic distribution of mesopelagic appendicularian Oikopleura villafrancae in the Adriatic

Investigation of deep sea plankton is limited because the deep sea net sampling is time consuming especially is specialized equipment such as multinet systems is not available. We here present rare insight in yearly cycle and size distribution of mesopelagic appendicularian Oikopleura villafrancae. Appendicularians are a group of pelagic tunicates known for their short life cycle and unique mode of feeding using a structure called the appendicularian house. Their house contains a set of filters which enables them to feed on submicron particles. Appendicularians have not been known to exhibit any substantial vertical migration. In order to investigate ecology of mesopelagic appendicularian Oikopleura villafrancae we sampled open South Adriatic from the surface to the 1200 m depth during the course of three years in following layers using Nansen closing nets: 0-50, 50-100, 100-200, 200-300, 300- 400, 400-600, 600-800, 800-1200 m. The samplings were contucted during all seasons. We determined abundance of the O. villafrancae in each layer as well as measurements of tail length, tail musculature width, trung length and endostyle length. Our results show that population of O. villafrancae is vertically distributed in depth layers from 200-1200 m in a way that shortest inndividuals are consistently found only in top layers while progressively larger individuals are found in deeper layers. The abundance of O. villafrancae is lowest in winter and autumn months while in spring and summer it is the greatest. Morphological data does not show any discrepancies within the population which would indicate presence of cryptic species or subspecies as indicated by Fenaux (1992) by describing subspecies Oikopleura villafrancae indentacauda in addition to species Oikopleura villafrancae.

vertical distribution ; ontogenetic distribution ; mesopelagic ; Appendicularia ; Oikopleura villafrancae

nije evidentirano