C. Pergentmartini et G. Pergent, LEPIDOCHRONOLOGICAL ANALYSIS IN THE MEDITERRANEAN SEAGRASS POSIDONIA-OCEANICA STATE-OF-THE-ART AND FUTURE-DEVELOPMENTS, Oceanologica acta, 17(6), 1994, pp. 673-681
After blade shedding in the seagrass Posidonia oceanica, leaf sheaths
remain attached to the rhizome and can persist for several decades wit
hin a ''matte'' They show, according to their insertion rank, cyclical
variations in parameters such as thickness and tissue structure. Thes
e cycles are always annual, and may be influenced by environmental par
ameters such as light, temperature or water movement. The study of cyc
lic changes in Posidonia oceanica sheaths is thus a technique that can
be used to investigate past changes in the near-shore environment. By
analogy with dendrochronology, this study is termed lepidochronology.
A number of applications of lepidochronological analysis have already
been successfully tested : (i) Estimation of the growth rate and annu
al production of rhizomes; (ii) Modelling of leaf renewal cycles (e.g.
rhythm of leaf formation and of leaf fall, leaf longevity); (iii) Det
ection and dating of previous flowering from the remains of flower sta
lks inserted between the sheaths (iv) Evaluation of primary production
. This new technique is much faster than the classic methods and has t
he further advantage that primary production for previous years can al
so be estimated. Twenty-two sites in the Mediterranean sea? between 0.
7 and 32.0 m depth have been investigated using this technique. The po
ssibility that chemical events (e.g. heavy metals) may be memorized in
Posidonia oceanica sheaths and rhizomes is currently being investigat
ed.