Phytosociological classification of seagrass communities
Den Hartog, Cornelis
A phytosociological classification of the seagrass communities of the world is proposed. All communities can be arranged within the seagrass formation which comprises 6 classes. These have been defined on the basis of several criteria, particularly floristic composition (on the genus level) of the angiosperm component, biocomplexity, temporal stability, and geographical distribution. The classification has been elaborated at the levels of order and alliance, but no attempts have been made to present a detailed account at the level of the association. It is the opinion of the author that the associations are the local expressions of the alliances. As the communities in this presentation are taxocoenoses, associations with the same dominant angiosperm(s) may have a completely different accompanying algal flora or fauna component, depending on geographical area, salinity, substrate characteristics, water movement characteristics, illumination (depth), seasonality, etc. A short history is given of the classification of these communities in the past. Further, the used criteria have been discussed. Attention has been given to the demands of the nomenclature rules, and their limited applicability for the special case of the seagrass communities. Additionally a short description of the Ruppietea is given, as one marine angiosperm community of very sheltered marine environments does not fit within the seagrass formation, but can be classified without any problems in this class of water-plant communities of shallow, poikilosaline coastal and continental waters.