Reconstruction of seagrass dynamics: age determinations and associated tools for the seagrass ecologist

Abstract

All seagrasses are rhizomatous plants that grow by reiteration of a limited set of modules. Their past growth history can therefore be reconstructed from the scars left by abscised leaves and flowers on the long-lived rhizomes or the seasonal slgnals Imprinted in the frequency and size of their modules. We provide here the basic foundations and assumptions of these reconstruction techniques and the calculations involved in their application. We then show their reliability and potential to quantlfy an array of ecological processes, such as plant demography, leaf and rhlzome production, flowering ~ntensity, and seagrass responses to anthropogenic perturbations, based on our recent studies of Mediterranean, Caribbean and Indo-Pacific seagrass species. Reconstruction techniques have also proven useful in demonstrating the role of seagrasses as tracers of sedlment movement over seagrass beds and the rates of colonisation and expansion of seagrass patches. These reconstruction techniques should provide a powerful tool to improve our knowledge of seagrass species and populations from remote areas based on a single or just a few visits This should, therefore, allow us to sample many seagrass meadows using limited resources, thus generating a strong foundation for the study of comparatlve seagrass ecology and testing of theories previously applied to terrestrial plant populations.

Presencia de Cistenides Elhersi Hessle, 1917 (Polychaeta Perctinariidae) en aguas someras magallánicas habitadas por praderas de Ruppia Filifolia: Evidencia de Euribatia, Eurihalididad y Euritermia?

“…ruppia se considera relativamente similar a un pasto marino (Duarte, 1991), donde el crecimiento es de tipo horizontal con ramificaciones monopodiales verticales generadas por crecimiento vegetativo que continúan en ramificaciones simpodiales durante la época de floración (Verhoeven, 1979;Bigley & Harrison, 1986). De modo similar a los pastos marinos, las plantas de ruppia crecen por reiteración de un grupo limitado de nodos (Duarte et al 1994). La unión de los rizomas y raíces retienen en forma selectiva una gran cantidad de sedimentos que permiten actuar como un hábitat bioingeniero disponible para una serie de otros organismos acuáticos bentónicos (Castro & Huber, 2007).…”

Inter-annual variation of shoot density and biomass, nitrogen and phosphorus content of the leaves, and epiphyte load of the seagrass <i>Posidonia oceanica</i> (L.) Delile off Mallorca, western Mediterranean

“…They can be obtained either through continuous research and monitoring efforts or, in a few cases, through the reconstruction of past seagrass performance and environmental conditions. For example, the longevous Mediterranean seagrass Posidonia oceanica (L.) Delile allows us to estimate past leaf and rhizome production using age reconstruction methods (Pergent and Pergent-Martini, 1990;Duarte et al, 1994); the pluri-annual data obtained can then be used to evaluate the effects of natural (Marbà and Duarte, 1997) or anthropogenic (Guidetti, 2001;Marbà et al, 2006) environmental changes on plant performance. The contamination history of P. oceanica meadows may be retrieved by analyzing the concentration of contaminants in seagrass parts of different ages (Calmet et al, 1988;Romeo et al, 1995).…”

Spatial and temporal variability of seagrass at Lizard Island, Great Barrier Reef

“…Vertical rhizome elongation rate was estimated by measuring the length of the fourth internode back from the meristem (representing a mature plant part) of each seagrass vertical shoot and then dividing by the leaf plastochrone interval (Short and Duarte 2001). Horizontal rhizome elongation rate was calculated by dividing the length of the rhizome between two consecutive vertical shoots by the difference in the ages of the two shoots (Duarte et al 1994). All measurements were performed on photographs of seagrass samples using ImageJ (Rasband 2012).…”

“…The number of leaf scars plus the number of standing leaves per shoot for each shoot on the rhizome were counted to obtain a shoot age estimate in days, and the number of scars per shoot was multiplied by the leaf plastochrone interval (time to produce a new leaf; Duarte et al 1994). Vertical rhizome elongation rate was estimated by measuring the length of the fourth internode back from the meristem (representing a mature plant part) of each seagrass vertical shoot and then dividing by the leaf plastochrone interval (Short and Duarte 2001).…”