The radiolaria are a group of marine eucaryote protists with a skeleton of silica which is incorporated in the sediments when these organisms die. In the Arctic Ocean this group was previously poorly known, but in recent years a better understanding of species diversity, faunal associations, origin of the present radiolarian community established, and possible endemism.
The Arctic Ocean is very special with respect to its oceanographic structure and its extreme ecological living conditions. The number of species in the Arctic Ocean is low with only 64 identified so far, many similar to those from the Norwegian Sea fauna. None of the species that are dominant in the Bering Sea have been observed in the Chukchi Sea , and it is therefore assumed that there is only a negligible migration from the North Pacific into the Arctic Ocean .
The shallow oceans outside the Eurasian coast have a species composition with a domination of the group called Nassellaria, and it differs drastically from the fauna in proper polar basins where the group Spumellaria dominates. The Arctic Ocean has had conditions similar to the present day, only during earlier interglacial periods, such as the marine isotope stages MIS 5 and 7. This implies that the radiolarian fauna that was present in the Norwegian Sea only entered the Arctic Ocean during warm interglacial periods. The arctic fauna is expanding southwards during the cold arctic periods.
We are now focusing on a group within Spumellaria, the genus Actinomma, which today is dominating the radiolarian fauna in the Arctic Ocean . This group has a wide range in its skeletal morphology, which can be explained through genetic changes within the arctic Actinomma population. Recently two new species has been described as endemic for the Arctic Ocean . If these species originate from species that invaded the Arctic Ocean then genetic drift and allopatric speciation can partly explain the origin of these morphologically new species. A further sympatric speciation can explain the remarkable richness in skeletal morphology within the Arctic Ocean actinommids. These morphological changes occurred within a narrow time frame (Holocene, the last 11 600 calendar years), suggesting a rapid and active speciation, an ongoing process that we will continue to study in the years to come.
References
Bjørklund, K.R., Kruglikova, S.B., 2003. Polycystine radiolarians in surface sediments in the Arctic Ocean basins and marginal seas. Mar. Micropaleontol. 49, 231-273.
Kruglikova, S.B., Bjørklund, K.R., Hammer,Ø., and Anderson,O. R. Endemism and speciation in the polycystine radiolarian genus Actinomma in the Arctic Ocean : Description of two new species Actinomma georgii n. sp. and A. turidae n. sp. In press. Mar. Micropaleontol.