THE ECOLOGICAL POTENTIAL OF THE (COCCO)LITHS VERSUS (COCCO)SPHERES
Mário Cachão (1), Anabela Oliveira (2) , Alexandra Silva (3), Markus Geisen (4), Patrizia Ziveri (5), Alexandra Broerse (5), Ian Probert (6)
1 Centro e Departamento de Geologia, Faculdade de Ciências, University of Lisbon, Rua Escola Politécnica, No 58, P-1294 Lisboa CODEX, Portugal, mcachao@fc.ul.pt
2 University of Algarve / Marinha - Instituto Hidrogr‡fico, Rua das Trinas, No 49, P-1200 Lisboa, Portugal, aboliveira@mail.telepac.pt
3 Dep. Zoologia e Antropologia, Faculdade de Ciências, University of Lisbon, Ed. C2, 3¼ Piso, P-1749-016 Lisboa, Portugal, alexandra.ds@mail.telepac.pt
4 Palaeontology Dept., The Natural History Museum, London, SW7 5BD, UK M.Geisen@nhm.ac.uk
5 Faculteit der Aardwetenschappen, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands, zivp@geo.vu.nl
6 Laboratoire de Biologie et Biotechnologies Marines, Université de Caen Basse Normandie 14032 CAEN, France, Billard@ibba.unicaen.fr
Most of the micropaleontological oriented works performed upon coccolithophore communities developing in the upper layers of the ocean water column routinely include counts of coccospheres (here after referred as spheres, for simplicity) and heterococcoliths (here after simply referred to as liths) both structures 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 the coccolithophore ecosystem information may be lost.
By establishing a per species comparison between the abundance of liths (considered as 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, in press).
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 was ecologically performing:
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;
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;
Higher factor loadings for liths relative to spheres may indicate decay of the species population with certain biostratonomic processes (e.g. dispersion, contamination, ressuspension, 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 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 3050 m depth off Somalia (MST-9: 10¼45'N; 53¼34'E), to determine how the sinking coccolithophore structures respond to an upwelling hydrographical system.
REFERENCES
Cachão, M. & Oliveira, A. (in press) - (Cocco)liths versus (cocco)spheres: Approaching the ecological performance of Coccolithophores Journal of Nannoplankton Research..
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