Clonal building, simple growth rules and phylloclimate as key steps to develop functional–structural seagrass models

Abstract

The repetitive clonal growth of the seagrasses Zostera noltii Hornem. and Cymodocea nodosa Aschers at the module level was used to implement a deterministic, individual-based, numerical model using the simplest growth rules. Inter-and intraspecific variability in plant morphology and meadow attributes was simulated, and the results yielded by the model were compared with an existing large data set recorded for both species. The model outputs showed that intra-and interspecific morphological variability can be accurately described (r = 0.99, p < 0.0001, n = 19) by a restricted number of parameters (plastochrone interval [PI] and elongation rates for rhizome [RER] and leaf [LER], which are species-specific parameters). Interspecific differences in meadow properties were recorded; however, simulated values were double those observed. This result was mainly attributable to a lack of densitydependence phenomena in the model assumptions, revealing the importance of such phenomena in structuring seagrass populations. In general, species with high PIs displayed longer modules (leaves and internodes) and lower shoot densities, whereas species with lower PI values developed shorter modules and crowded stands. This result corresponds with the relationship indicated by the self-thinning law and by previous studies. The model also showed that plant morphology arises as an emergent property of a simple set of growth rules acting at the module level, and that plant dynamic parameters can be tuned by seagrasses in response to their local environmental conditions. Thus, the whole-plant response to the environment can be determined by the sum of all the modular responses. This model, together with a better knowledge of the regulation of plant dynamic parameters by control variables (light, temperature, nutrients, etc.), provides a conceptual framework that allows the incorporation of module, plant morphology and meadow properties into functional-structural seagrass models, in which feedbacks among plant morphology, plant development and phylloclimate (i.e. the physical environment actually perceived by each individual organ or plant population) can be included.

Direct effects of current velocity on the growth, morphometry and architecture of seagrasses: a case study on Zostera noltii

“…4). In agreement with Brun et al (2006), the correlation observed in Fig. 4 between PI and the relative maximum production of photosynthetic tissue suggests that there is a mechanism that modifies the AG/BG ratio.…”

“…Accessibility to water column resources may also account for the maximum GR observed in HV plants. However, the effect of GR is by itself insufficient to fully explain the changes in morphometry and recruitment observed at HV, because these changes will require an additional modification of biomass allocation pattern (Brun et al 2006). According to the model developed by Brun et al (2006), the divergences observed in this study between growth and recruitment patterns (Fig.…”

Role of two contrasting ecosystem engineers (Zostera noltii and Cymodocea nodosa) on the food intake rate of Cerastoderma edule

“…in the intertidal areas, whereas more continuous beds of Z. noltii and Cymodocea nodosa (Ucria) Ascherson thrive in the lower intertidal and shallow subtidal zones. In the study site, Z. noltii develops in denser stands but with a shorter canopy height compared to C. nodosa (see Brun et al 2006 for further details).…”

Interactions of light and organic matter under contrasting resource simulated environments: the importance of clonal traits in the seagrass Zostera noltii

“…Most studies have been carried out looking at the effect of light reduction on seagrass physiology, growth, or meadow attributes (see review table in Brun et al, 2006). In comparison, few studies have been devoted to investigating the effect of OM loads (Terrados et al, 1999;Cancemi et al, 2003), while the combined effects of light and OM on seagrass growth, survival and photosynthetic activity have rarely been reported (Short et al, 1995;Holmer & Laursen, 2002;Holmer et al, 2005).…”