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The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass


The association of Phaeocystis spp. with small pennate diatoms during three Phaeocystis-dominated spring blooms were investigated in the Eastern English Channel (2003 and 2004) and in coastal waters of Western Norway during a mesocosm experiment (2005). In each of these studies, colonization of the surface of large Phaeocystis spp. colonies by small needle-shaped diatoms (Pseudo-nitzschia spp.) were observed. In the English Channel the diatom Pseudo-nitzschia delicatissima colonized the surface of large (>100 μm) Phaeocystis globosa colonies. The abundance of Pseudo-nitzschia delicatissima reached 130 cells per colony and formed up to 70% of the total carbon associated with Phaeocystis cells during late bloom stages. In Norwegian waters, the surface of large (>250 μm) Phaeocystis pouchetii colonies were colonized by Pseudo-nitzschia cf. granii var. curvata and to a lesser degree by other phytoplankton and protist species, although the abundance of these diatoms was never greater than 40 cells per colony. Based on these observations we suggest that diatoms utilize Phaeocystis colonies not only as habitat, but that they are able to utilize the colonial matrix as a growth substrate. Furthermore, these observations indicate that a considerable fraction of biomass (chlorophyll) associated with Phaeocystis colonies, especially large colonies concerned with intense and prolonged blooms, are due to co-occurring plankton species and not exclusively Phaeocystis cells.

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We are indebted to Dr. Lucie Courcot from Universite du Littoral Cote d’Opale, Wimereux, France for SEM photographs that were useful for identification of the Pseudo-nitzschia delicatissima. We thank the crews of R.V. Sepia II and Côtes de la Manche for their help during cruises in the Eastern English Channel, as well as staff of Université of Littoral and University of Bergen for their technical support and help. Anna Boyette (Skidaway Institute of Oceanography) prepared the figures. This work was part of CPER “Bloom of Phaeocystis” and “PNEC Manche Orientale” French regional and national programs for Eastern Channel Monitoring. Jens C. Nejstgaard was supported by the Norwegian Research Council (152714/120). This study was also funded by the US National Science Foundation Office of Polar Programs grant (OPP−00-83381) and the US Department of Energy Biotechnology Investigations–Ocean Margins Program (FG02-98EF 62531).

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Correspondence to Andrey F. Sazhin.

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Sazhin, A.F., Artigas, L.F., Nejstgaard, J.C. et al. The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass. Biogeochemistry 83, 137–145 (2007).

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  • Biomass estimate, colonies
  • Colonization
  • Phaeocystis bloom
  • Pseudo-nitzschia species