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Marine Nanoplankton Body Scales Imaged by AFM

AFM as a technique provides a range of new opportunities for viewing and manipulating living and non-living marine specimens under ambient conditions. The area of application in marine sciences is yet unexplored. Nanoflagellates, the "hidden" flora of phytoplankton populations, are a major component of the phytoplankton, accounting for up to 90 % of the total biomass and responsible for more than 50 % of primary production.(1, 2) These small organisms, 2-20 &micro ; ; m in size, are largely unrecognised when standard methods are used for plankton collection, preservation and examination by light microscopy. However, improved methods of phytoplankton sampling, culturing and fixation, combined with extensive use of the electron microscope, have resulted in the recognition and description of many nanoflagellates, as well as increased knowledge of their global distribution.(3) Chrysochromulina (division Haptophyta) appears to be distributed worldwide. Members of this genus have two smooth flagella and a haptonema, the length of which varies depending on species. One or several types of small organic scales, arranged in layers, form the cell covering. The basic type of scale is generally an oval, two-layered plate with fibrils arranged radially on the proximal surface and a more variable pattern on the distal surface. The species within the genus can be distinguished mainly by the morphology of the organic body scales, which typically requires electron microscopy (4) ; cell size and flagellar and haptonema length are supporting features used to differentiate between species (3). Since the scale formation in any case is species-specific, their occurrence represents a finger-print of the algal species that are, or that have been, present in the ecosystem.(5) We are presenting the first AFM images of Chrysochromulina body scales trapped inside the giant gel of the northern Adriatic sea (Figures 1 and 2). Unlike many other forms of microscopy, atomic force microscopy does not require any stains, contrast agents, or conductive coatings that can cause partial obstruction of the actual sample. It is a nondestructive method that allows the sample to be reused for additional analyses over time. In addition, AFM sample preparation is fairly simple and quick. References: (1) Malone, T. C. 1980. Algal size. In: (I. Morris, ed.) The physiological ecology of phytoplankton. Blackwell Scientific Publications, Oxford. pp. 433– 463. (2) Hallegraeff, G.M. 1981. Seasonal study of phytoplankton pigments and species at a coastal station off Sydney: importance of diatoms and nanoplankton. Mar. Biol. 61: 107– 118. (3) J-M LeRoi, G. M. Hallegraeff. 2004. Scale-bearing nanoflagellates from southern Tasmanian coastal waters, Australia. I. Species of the genus Chrysochromulina (Haptophyta). Bot. Mar. 47: 73-102. (4) E. Dahl, E. Bag&oslash ; ; ien, B. Edvardsen, N. C. Stenseth. 2005. The dynamics of Chrysochromulina species in the Skagerrak in relation to environmental conditions. J. Sea Res. 54: 15-24. (5) H. Landa, G. Bratbak, M. Heldal. 2004. Abundance and dynamics of free flagellate scales in marine costal ecosystems. Aquat. Microb. Ecol. 37: 55-62.

nanoplankton body scales; Chrysochromulina; AFM; atomic force microscopy

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