Autochthonous seagrasses

Seagrasses are flowering plants that undergo their whole life cycle within shallow coastal habitats. All species share analogous architectural and growth patterns. They are modular plants composed of units arranged by a set of modules: a piece of rhizome, a bundle of leaves (shoot) attached to the rhizome and roots. Four species occur in the Mediterranean bioregion: the endemic Posidonia oceanica, the tropical Cymodocea nodosa and the temperates Zostera marina and Z. noltii. Posidonia oceanica is the largest one, with very slow growth rates and being considered the climax stage of Mediterranean subtidal bottoms. Meadows extend on 2.5-4.5 millions ha that is close to 25 % of the Mediterranean basin shallower than 50 m. Cymodocea nodosa, Zostera marina and, particularly, Z. noltii are smaller in size but fast growing as typical of the pioneering species. Seagrass meadows are among the most productive ecosystems on earth, providing important ecological services: nursery grounds, biofilters, water cleaners, coastline protectors and carbon sinks. However, despite its paramount importance there is widespread regression of such habitats. Although the four Mediterranean species have been assigned to the Least Concern category of the IUCN Red List, P. oceanica populations are experiencing the highest rate of decrease. Given the extremely slow growth rate of this species such losses are virtually irreversible. Direct and indirect (i.e., climate change) human activities affecting mostly to physical integrity of habitats, sediment and water quality, coastal sedimentary balance or species composition are argued to be the main drivers of seagrass decline in the Mediterranean Sea. European (and Mediterranean) countries, aware of the key important role that seagrasses play, have established management and conservation plans for these habitats. Thereafter, the aim of the present contribution is to present basic information about the biology and ecology of the Mediterranean seagrasses, the main threats facing these habitats, as well as to provide some information on the main conservation and management strategies