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Mário Cachão, Anabela Oliveira, Alexandra Silva, Markus Geisen, Patrizia Ziveri, Alexandra Broerse, Ian Probert:
The ecological potential of the (cocco)liths versus (cocco)spheres
(Talk)

Most of the micropalaeontologically-oriented works performed upon coccolithophore communities developing in the upper layers of the oceanic water-column routinely include counts of coccospheres (hereafter referred to as spheres, for simplicity) and heterococcoliths (hereafter simply referred to as liths), since both structures are found together on the filters. Subsequently, the liths are generally converted to (virtual) cells by defining a certain number (constant) of liths per cell (sphere) per species. By doing so, a meaningful and probably very important part of coccolithophore ecosystem information may be lost.

By establishing a per species comparison between the abundance of liths (considered to be the 'memory' of the system) versus spheres, a better interpretation of the ecological behaviour and/or the biostratonomic status of some of the major coccolithophore species is pursued. The method here described was applied to 32 water-column samples retrieved from two cruises carried out off Portugal: CORVET cruise, November, 1996 and CLIMA cruise, December, 1997 (Cachão & Oliveira, 2000).

By comparing the relative position of the liths against the spheres of a certain species, in factor diagrams, it may be deduced how the species were ecologically performing: (i) similar factor loadings for the spheres and the liths of a certain species (close to each other in the factor diagram) may indicate steady and continuous development of the species during a more-or-less extended period of time prior to sampling; (ii) higher factor loadings for spheres relative to liths (spheres located on the extremes of the diagram axes apart away from the liths, which are located closer to the origin of the factors) may indicate new (exponential) growth of cells of the species, meaning favourable conditions for its development. In these circumstances, physical-chemical properties of the water-masses reflect the species' ecological optima; (iii) higher factor loadings for liths relative to spheres may indicate decay of the species population, with certain biostratonomic processes (e.g. dispersion, contamination, resuspension, etc. of the liths) being more important than ecological ones. In these circumstances, physical-chemical properties of the water-masses may reflect a low degree of, or no, relationship with the ecological preferences of the species.

These results are further discussed and compared to data retrieved from cultures of several coccolithophore species integrated in the scientific goals of the EC-TMR CODENET network. The method is also applied to data retrieved during May of 1992 to February, 1993, from sediment traps located at 1032 and 3050m depths off Somalia (MST-9: 10º45'N, 53º34'E), to determine how the sinking coccolithophore structures respond to an upwelling hydrographical system.

Reference

Cachão, M. & Oliveira, A. 2000. (Cocco)liths versus (cocco)spheres: approaching the ecological performance of coccolithophores Journal of Nannoplankton Research, 22: 29-34.

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