Competition between mediterranean clonal seagrasses.

Abstract

[eng] The human impact on the global environment has caused a fast regression of the seagrass meadows, which are a crucial part of the marine ecosystem. The aim of this work is to propose a microscopic clonal growth model of seagrass growth to understand better the dynamics of the meadows and the factors that affect their development. In particular, the proposed model will address the problem of two seagrass species interacting in the same spatial region. The species used will be the Mediterranean endemic species of seagrass Cymodocea nodosa and Posidonia oceanica. To build the final model, the first step is to start from the study of models of clonal growth of a single seagrass specie without interaction. The results show that the fate of the patches depends on the difference between the intrinsic branching rate and the mortality rate. Initially, the growth of the patch is governed by a branching independent process and it changes to a radial linear expansion after some years, when a plateau density is reached. We have extended the models adding the presence of a local interaction. This local interaction is introduced through a dependence of the total branching rate with the local density. A parameter study has been used to identify different regions of stable populated solutions or stable extincted solutions. This acts as a basis for the development of the novel model of cross-interaction between the two seagrass species. Two variants of the model have been proposed: one that gives equal weight to both seagrass species (ECI) and the other that gives more weight to Posidonia oceanica due to its biological characteristics (DCI). The different cases of study reveal that the overall dynamics of the patches of seagrass is determined by the intrinsic branching rate of the seagrass specie. Moreover, the cross-interaction between species influences the density of the patches. In addition, we have determined that ECI displays more reasonable dynamics than DCI. The work is expected to give the tools and the basis to more extended models of two interacting seagrass species