On the consortium of the tintinnid Eutintinnus and the diatom Chaetoceros in the Pacific Ocean
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The morphology and distribution of the diatoms Chaetoceros tetrastichon and Ch. dadayi as epiphytes on the loricae of the tintinnids Eutintinnus apertus and E. pinguis investigated in the open waters of the Pacific Ocean. The Eutintinnus–Chaetoceros consortia was encountered in 38 of the 52 sampling stations from 34°N to 33°S, and together were among represented the most wide-spread species. The abundance was low with a maximum of 32 consortia l−1 and E. apertus was often the most abundant species of the genus. The free-living Eutintinnus congeneric species showed a wider vertical distribution, whereas E. apertus–Chaetoceros tended to be near the surface. The success of E. apertus in consortium with Chaetoceros may be due to increase of the clearance rate and/or the lower susceptibility to predation. Chaetoceros modifies its morphology to adapt the epiphytic life, especially Ch. dadayi. The shorter curved setae may facilitate the transfer to the lorica of the daughter tintinnid after the cell division. The free-living Ch. tetrastichon and Ch. dadayi are very rare and Chaetoceros remained attached to empty loricae or encysted tintinnid cells. This suggests that the Eutintinnus–Chaetoceros consortium is obligate for the success of the diatom and renders the tintinnid more competitive versus congeneric species.
KeywordsKuroshio Current Congeneric Species Prochlorococcus Oral Diameter Oligotrophic Water
The studies in the NE and equatorial Pacific were supported by a fellowship of the European Commission (ICB2-CT−2001-80002) held at the University of Tokyo with K. Furuya as host. I am grateful to the scientists and crew of R/V Soyo Maru (Nat. Res. Inst. Fish. Sci.), R/V Hakuho Maru (ORI, Tokyo University), R/V Mirai (JAMSTEC) and R/V L’Atalante (IFREMER). I thank to H. Claustre for the seawater samples and J. Ras for collecting assistance. I thank S. Coale for improving on the manuscript. This is a contribution to a Grant-in-aid for Creative Basic Research (12NP0201, DOBIS) from the MEXT, Japan; BIOSOPE of the LEFE-CYBER and the French IFB ‘Biodiversité et Changement Global’ programs.
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