Biology of Oithona similis (Copepoda: Cylopoida) in the Arctic, Antarctic and North Sea
Final Report Abstract
The aim of this study was to ascertain by morphological and genetical means whether Oithona similis is a conglomerate of cryptic species. This study concentrated on three different investigation areas: the Arctic Ocean, the Southern Ocean and the North Sea. These areas are inhabited by O. similis and four congeners: O. frigida (Southern Ocean), O. atlantica (Arctic Ocean), O. nana (North Sea) and O. plumifera (North Sea). O. similis is an important and abundant species in all these. This study clearly showed that Oithona similis is not a truly cosmopolitan species, but a conglomerate of several cryptic species. Within the nominal O. similis two different species were found in the Southern Ocean, the same holds true for the Arctic Ocean. Each of the species in the Arctic Ocean is represented by one single individual. Hence, more individuals are needed for confirmation, but the results showed that at least two different cryptic O. similis species occur in both regions. The CO1- sequence of the O. similis female from the North Sea differed from the sequences of the species from the other regions. Further individuals from the North Sea have to be examined to confirm this status as well as to investigate whether this area is inhabited by more than one cryptic O. similis species. No morphological differences within the appendages of the swimming legs were found among individuals of the Oithona similis species groups from the Southern Ocean, the Arctic Ocean and the North Sea. Eventually other morphological criteria could be used to distinguish among the cryptic Oithona species. Due to constrains in handling time, these were the only characters that could be used for a quick decision. Further examinations of Oithona similis individuals from the study areas are needed to decide whether the different clusters obtained from the genetic analysis represent distinct species.
